Low power dissipation touch plane interface circuit
Contents
1. 14 continued STEP REGISTER EFFECT TEST RESULT 178 0402000 Pull X high Short Check High Y to VSS Touch Detect Operational bit 178 0404000 X high Short Check High Y to VSS Touch Detect Operational bit 180 0420000 X high Short Check High touch sY to VSS Touch _ Detect screen bit pressed or shorted Low No touch screen press The following table summarizes the operation of the analog switch matrix 104 during step 178 180 for a 7 wire touch screen STEP REGISTER EFFECT TEST RESULT 178 0401000 Pull X high Short Check High X to VSS Touch Detect Operational bit 178 0402000 Pull X high Short Check High Y to VSS Touch Detect Operational bit 178 0404000 Pull X high Short Check High Y to VSS Touch Detect Operational bit 178 0408000 Pull X high Short Check High sX to VSS Touch Detect Operational bit 178 0410000 Pull X high Short Check High sX to VSS Touch Detect Operational bit 180 0420000 Pull X high Short Check High touch sY to VSS Touch Detect screen bit pressed or shorted Low No touch screen press In the above examples infinite impedance open circuit and relative impedance sensing techniques are used to test touch screen resistances Similar techniques could also be applied to perform other types of impedance sensing for example in connection with capacitive touch screens Vari ous capacitance sensing2. NI U3LU3ANOO ig U S Patent Feb 5 2008 Sheet 7 of 11 US 7 327 354 B2 SCAN Y AXIS TAKE 4 8 16 OR 32 SAMPLES STORING MAX MIN AND AVERAGE TAKE 4 8 18 OR 32 SET X INT PENDING X FIG 6 0 7 327 354 2 Sheet 8 of 11 Feb 5 2008 U S Patent L Old 8 Ualsip3u 20 jg DONE XVW NIIA UN 092 02151039 333 sdi NIW uos 082 NOLLVIA3Q m ualsio3H 7 gt waisiogd 862 13196 XVWA atvinWwnoov y9 ee M3iSlO3H 262 4 XVWX 195 cc 9 9 YOLVOIANI 6 7119 g E walsiogy 822 AWC le ans A1SV 9 Z ozz 152 151934 uH3JLSIO3M UN NIWA X 151 JOULNOD ave HOLVOIONI 982 S3 18VN3 NIWX INdNI osz QU Ld 2LNI 06c 0 7 327 354 2 Sheet 9 of 11 Feb 5 2008 U S Patent ag Old 98 Sis V8 Old U S Patent Feb 5 2008 Sheet 10 of 11 US 7 327 354 B2 Joe U S Patent Feb 5 2008 Sheet 11 of 11 US 7 327 354 B2 11 US 7 327 354 B2 1 LOW POWER DISSIPATION TOUCH PLANE INTERFACE CIRCUIT CROSS REFERENCE TO RELATED APPLICATIONS This application is a continuation of U S application Ser No 09 677 103 Sep 29 2000 now U S Pat No 6 753 853 and entitled LOW POWER DISSIPATION TOUCH PL
3. sX or sV indicating that the terminal 128 is adapted to be operably connected to the terminal of 8 wire touch screens and is adapted to be operably con nected to the sV terminal of 7 wire touch screens For 4 wire and 5 wire touch screens the terminal 128 is not utilized The sixth terminal 130 is labeled sX or indicating that the terminal 130 is adapted to be operably connected to the sX terminal of 8 wire touch screens and is adapted to be operably connected to the sV terminal of 7 wire touch screens For 4 wire and 5 wire touch screens the terminal 130 is not utilized The seventh terminal 132 is labeled sY or wiper indicating that the terminal 132 is adapted to be operably connected to the sY terminal of 8 wire touch screens and is adapted to be operably con nected to the wiper terminal of 7 wire touch screens For 4 wire and 5 wire touch screens the terminal 132 is not utilized Finally the eighth terminal 134 is labeled sY indicating that the terminal 134 1 adapted to be operably connected to the 5 terminal of 8 wire touch screens For 4 wire 5 wire and 7 wire touch screens the terminal 134 is not utilized The analog switch matrix 104 allows the terminals 120 134 to be selectively connected to and V power supply terminals to an analog input of the A D converter 102 and to the voltage reference inputs ofthe A D converter 102 In the case of the terminal 120 the termin
4. 100 then the process proceeds to step 160 At step 160 it is determined whether a 4 wire touch screen is connected or whether a 5 wire touch screen is connected The following table summarizes the operation of the analog switch matrix 104 during step 160 REGIS STEP TER EFFECT TEST RESULT 160 0404601 Pull X high Short ADC High 4 wire Y to VSS conversion on touch screen connected Low 4 wire touch screen pressed or shorted or 5 30 35 40 45 50 55 60 65 10 continued REGIS STEP TER EFFECT TEST RESULT wire touch screen connected 160 0402601 Pull X high Short ADC Conversion Y to VSS conversion value lt voltage and B C and 160 0600601 Pull X high Short ADC D lt F and E lt Y to VSS conversion on 5 voltage wire touch 160 0401601 Pull X high Short ADC screen X to VSS conversion on Conversion X voltage value gt C 160 0800EO4 Pull Y high Short ADC orB gt Cor X to VSS conversion on D gt For E gt Y voltage F 4 160 0801604 Pull Y high Short ADC wire touch X to VSS conversion on screen Y voltage E 160 0804604 Pull Y high Short ADC Y to VSS conversion on Y voltage F The first step is to determine if a 4 wire touch screen can be directly detected This is done by determining whether the X axis and Y axis layers of the screen are connected In the case of a 5 wire touch screen the same layer is
5. 6 is usable in connection with any form of operator interface the process of FIG 6 is particularly useful in connection an interface that emulates a hardware mouse by receiving operator inputs and moving a mouse pointer across a touch screen in response Although the mouse pointer in a Windows interface is often an arrow that appears to point to a location other shapes are also extremely common Herein the term mouse pointer is used to refer to any graphic marker on a display that is intended to identify a location on the display The process of FIG 6 is preferably implemented using digital signal processing circuitry that is not part of the microprocessor 86 of the system on chip integrated circuit 70 This allows the touch screen to be serviced by a device other than the microprocessor thereby reducing micropro cessor overhead Even more preferably the process of FIG 6 is preferably implemented using discrete logic circuitry as opposed to another microprocessor The output of the discrete logic circuitry is an event notification preferably in the form of a hardware interrupt provided to the micropro cessor 86 which notifies the microprocessor 86 that the mouse pointer has moved by at least a predetermined amount and provides the microprocessor 86 with updated location information As a result the microprocessor 86 is interrupted only when touch screen movement is sufficiently significant Therefore intervention of the mi
6. DOCUMENTS 6 292 181 9 2001 Banerjee et al 6 445 383 1 9 2002 Chambers et al 4 908 620 A 3 1990 Fujisawa 6 611 257 8 2003 Dotson et al 4 942 514 A 7 1990 Miyagaki et al 6 753 853 6 2004 Dotson 345 173 5 014 051 5 1991 Lippmann et al 6 765 558 7 2004 Dotson 345 173 5 053 758 10 1991 Cornett et al 5 376 947 A 12 1994 Kuroda OTHER PUBLICATIONS 5 867 665 A 2 1999 Butman et al 5 880 411 3 1999 Gillespie et al The New IEEE Standard Dictionary of Electrical and Electronics 5 956 020 A 9 1999 D Amico et al 345 173 Terms 5th Ed 1983 p 1051 5 995 084 A 11 1999 Chan etal 345 173 Setup and User Manual Hampshire TSHARC 8 Touch Screen 6 037 930 A 3 2000 Wolfe et al Controller Board Revision 1 6 pp 3 amp 7 6 088 628 A 7 2000 Watanabe et al MDS 7121 Touch Screen Controller Data Sheet Printed Nov 16 6 091 031 A 7 2000 Lee et al 2000 Revised Oct 8 1999 pp 1 16 6 163 313 A 12 2000 Aroyan et al 6 229 472 5 2001 Nidhida cited by examiner U S Patent Feb 5 2008 Sheet 1 of 11 US 7 327 354 B2 Prior Art Prior Art FIG 1A FIG 1B Prior Art Prior Art FIG 1C FIG 1D 0 7 327 354 2 Sheet 2 of 11 Feb 5 2008 U S Patent Z r ul Y LL lt O Lu DNU 001 HL ooe119 U ejdsiq eoepelu pedAey uoeJos uon
7. In the case of a 5 wire touch screen current flows between each of the four terminals This current flow in turn causes power to be dissipated In contrast when the analog switch matrix 104 is in a touch detect configuration as in FIG 8A relatively little or no current flows to the X axis and Y axis layers from the analog switch matrix 104 as compared to the current that flows while the analog switch matrix 104 is in configuration shown in FIGS 8C and 8D Therefore relatively little or no power is dissipated by the X axis and Y axis resistive layers as compared to the power that is dissipated while the analog switch matrix 104 is in the configuration shown in FIGS 8C and 8D In practice in FIG 7 step 206 is performed in the following manner First the value stored in the MIN register 252 is subtracted from the value stored in the MAX register 254 This is accomplished by providing the value in the MIN sample register 252 to a multiplexor 272 and providing the value stored in the MAX sample register 254 to a multi plexor 270 The multiplexors 270 and 272 pass the maxi mum and minimum sample values respectively to a sub tractor circuit or any other form of comparator circuit 274 The difference is then compared to the predetermined maxi mum deviation XDEV stored in the register 280 This is achieved by providing the output of the subtractor circuit 274 to a multiplexor 276 which passes the difference to a comparator 278 The
8. Y in case a truly new location was determined The YINT flag is also set to cause the algorithm to skip step 230 on consecutive sample sets If the difference in step 232 15 less than the YMAX then the process proceeds to step 238 At step 238 just as in step 214 the new Y value is stored as the LAST Y register that is YLAST 1 set equal to Y and the YINT flag is also set When either interrupt flag is set the microprocessor is notified and the new X and Y values are read by the microprocessor and the XINT and YINT flags are cleared Thereafter the process returns to step 202 and waits for another touch press As has been described rather than sending a continuous information stream to the microprocessor when the touch screen is in use the logic circuit 250 interrupts the micro processor only when touch screen movement is sufficiently significant in order to minimize intervention of the micro processor in the scanning process FIG 9 presents a sim US 7 327 354 B2 21 plified graphical representation of this arrangement As shown in FIG 9 the values XMIN and YMIN stored in the registers 290 and 296 define a region 299 that surrounds the current location of a mouse pointer 298 The microprocessor 86 is not notified unless a touch is detected at a location outside the perimeter of the region 299 4 Exemplary Application Referring now to FIG 10 the system on chip integrated circuit 70 of FIG 2 is usable in a wide arra
9. or control networks 402 In addition to these components the indus trial control system may include a wide array of additional components In addition to providing operator controls and displaying status the operator interface 400 also executes a user program to control output status of the plurality of output devices based on input status information from the plurality 5 20 30 35 40 45 50 55 60 65 22 of input devices Thus the operator interface 400 of FIG 11 combines the functions of the programmable controller system 306 and the operator interface 300 of FIG 10 in a single integrated package The operator interface 400 preferably includes a touch screen sensor system such as shown in FIGS 1A 1D The operator interface 400 may or may not contain a dynamic display 410 that will display the input and output status of at least a portion of the plurality of input and output devices 401 As an alternative to a display a fixed graphic underlay may be used to represent the plurality of input and output devices 401 In either case the touch plane operator input device may for example be a 4 wire 5 wire 7 wire or 8 wire device each of which uses a different sensor system as previously discussed The operator interface 400 is provided with a system on hip integrated circuit 70 The integrated circuit 70 therefore includes the circuitry discussed above in connection with the preferred touch screen interfa
10. shorted High No touch screen press Referring now to FIG 4B a second method for determining a touch screen type is illustrated The second method is digital detection method that avoids using the A D converter 102 False A D converter readings can occur due to back ground noise and other problems For example some delta sigma converters produce invalid samples during resynchro nization An analog algorithm may reguire sampling and averaging to reject noise and false readings In addition when detecting differences between a 5 wire touch screen and a pressed 4 wire touch screen for example timing of the algorithm can be critical in the presence of intermittent or bouncing contact Although some re sampling may be reguired a digital method can help to avoid potential timing and sampling issues during the algorithm At step 172 it is f rst determined whether a touch screen is connected to the interface circuit 100 The first two parts of this step ensure that the Touch Detect circuit is working The following table summarizes the operation of the analog switch matrix 104 during step 172 STEP REGISTER EFFECT TEST RESULT 172 0000800 Short X to VSS Check High Touch Detect Operational bit 172 0040000 Pull X high Check Low Touch Detect Operational bit 172 047F000 Pull X high Short Check Low No X Y sX Touch Detect touch screen SX sY sY to bit connected VSS High touch Screen connected 1
11. systems In some applications the operator touch is made by a stylus or other device held by the operator In other applications the operator touches the screen directly Touch pads are similar in operation to touch screens except that they are not used in connection with a display device Touch pads are often placed adjacent the space bar on laptop computers to allow operator control of a mouse pointer Numerous other applications also exist For convenience the discussion will now focus on touch screens it being understood that the discussion is egually applicable to touch pads and other touch plane operator input devices In many touch screen systems a computer system is implemented using system on hip integrated circuits In a single chip these integrated circuits provide many of the functions that used to be spread among many integrated circuits For example in addition to the main microprocessor it is not uncommon to have other circuits such as specialized serial interfaces UARTs memory con trollers DMA controllers Ethernet interfaces display inter faces USB universal serial bus interfaces and so on as well as a touch screen interface used to acguire data from a touch screen A problem that has been encountered with system on chip integrated circuits adapted for use with touch screens is that there are many different types of touch screens For example some touch screens are relatively small e g three inches o
12. value stored in the XMIN register 290 which is received at the comparator 278 by way of the multiplexor 276 If the difference between the new X value X and the last X value XLAST is less than the XMIN value then this indicates that the movement in the X direction is not significant enough to warrant alerting the microprocessor 86 Therefore the process proceeds to step 224 discussed below which is the beginning of the scanning process for the Y axis If the difference between the new X value X and the last X value XLAST is not less than the XMIN value then this indicates that the movement in the X direction is significant enough to warrant alerting the microprocessor 86 that is so long as the movement in the Y direction is also significant enough to warrant alerting the microprocessor as discussed below The process in this event proceeds to step 212 where the difference between the new X value X and the last X value XLAST is compared to the XMAX value in the XMAX register 292 The purpose of this step is to verify that any movement in the touch location is not so large as to be unrealistic In FIG 7 step 212 is performed by comparing the output of the subtractor circuit 274 X XLAST to the value stored in the XMAX register 292 which is received by way of the multiplexor 282 If the difference is greater than XMAX it is assumed that this distance is too far for a touch input to possibly move in the short scan time i
13. 0 15 20 25 30 35 40 45 50 55 12 The operation is similar to the operation at step 150 as described above except that the terminal 120 is mea sured at the output of the inverting logic gate 106 Assuming a touch screen is connected it is next deter mined at step 174 whether a 4 wire or 8 wire touch screen is connected or whether a 5 wire or 7 wire touch screen is connected In this step the and X terminals are first manually shorted together at the touch screen connector The following table summarizes the operation of the analog switch matrix 104 during step 174 REGIS STEP TER EFFECT TEST RESULT 174 0840605 Pull Y high Short Check Low 5 wire sY to VSS Touch Detect bit or 7 wire touch Screen connected High 8 wire or 4 wire touch Screen connected If step 174 determines that a 4 wire or an 8 wire touch screen is connected instead of a 5 wire or a 7 wire touch screen then the process proceeds to step 176 where it is determined whether a 4 wire touch screen is connected or whether an 8 wire touch screen is connected The following table summarizes the operation of the analog switch matrix 104 during step 176 REGIS STEP TER EFFECT TEST RESULT 176 0820605 Pull Y high Short Check Low 4 wire sY to VSS Short Touch Detect touch screen Y and X bit connected together High 8 wire touch screen connected Regardless whether a 4 wire touch screen or an 8 wire t
14. 0 25 30 35 40 45 50 55 60 65 6 110 118 the configuration of the analog switch matrix 104 during a different mode of operation Different values may be stored in the registers 112 118 depending on which type of touch screen is used The analog switch matrix includes eight input output I O terminals 120 134 The first terminal 120 is labeled X or V indicating that the terminal 120 is adapted to be operably connected to the terminal of 4 wire and 8 wire touch screens and is adapted to be operably connected to the V terminal of 5 wire and 7 wire touch screens The second terminal 122 is labeled X or indicating that the terminal 122 is adapted to be operably connected to the X terminal of 4 wire and 8 wire touch screens and is adapted to be operably connected to the terminal of 5 wire and 7 wire touch screens The third terminal 124 is labeled or Z indicating that the terminal 124 is adapted to be operably connected to the terminal of 4 wire and 8 wire touch screens and is adapted to be operably connected to the Z terminal of 5 wire and 8 wire touch screens The fourth terminal 126 is labeled or Z indicating that the terminal 126 is adapted to be operably connected to the Y terminal of 4 wire and 8 wire touch screens and is adapted to be operably connected to the Z terminal of 5 wire and 7 wire touch screens The fifth terminal 128 is labeled
15. 4 further comprising obtaining at least one of an impedance and capacitance associated with the plurality of terminals to facilitate determining the touch screen type 16 The method of claim 14 further comprising setting the type of touch screen to one of a 4 wire 5 wire 7 wire and 8 wire type 17 The method of claim 14 further comprising sampling one or more voltages associated with the touch screen computing a maximum a minimum and an average voltage and storing the computed voltages 18 The method of claim 17 further comprising utilizing the stored voltages to determine a position of a touch on the touch screen 19 The method of claim 17 further comprising utilizing the stored voltages to detect a movement of a touch on the touch screen and sending a notification indicative of the movement to a microprocessor when the movement exceeds a threshold 20 A system that automatically configures a touch screen interface comprising means for sensing that a touch screen is coupled to the interface means for determining a type of touch screen and means for configuring the interface for the touch screen type
16. ANE INTERFACE CIRCUIT the entirety of which is incorporated herein by reference BACKGROUND OF THE INVENTION 1 Field of the Invention This invention relates to interface circuits for touch screens This invention also relates to methods of processing inputs from touch screens This invention also relates to integrated circuits that include interfaces for touch screens 2 Description of Related Art Touch plane operator input devices such as touch screens and touch pads are known Typically a touch plane operator input device provides a generally planar surface that is sensitive to the touch of an operator and is operative to provide one or more output signals indicative of the location of the touch on the plane The output signals may be based either on the raw data from a touch screen sensor system or may be based on processed data that provides X Y coordi nate information of the touch Touch screens are an enhanced type of computer display device that include a touch plane operator input device Touch screens are therefore capable not only of displaying information to an operator but also of receiving inputs from the operator Touch screens have been put to use in a wide variety of applications Such applications include consumer applications such as personal digital assistants PDAs digital audio playback systems internet devices and so on as well as industrial applications such as operator interfaces in industrial control
17. a2 United States Patent Dotson US007327354B2 US 7 327 354 B2 Feb 5 2008 10 Patent No 45 Date of Patent 54 LOW POWER DISSIPATION TOUCH PLANE INTERFACE CIRCUIT 75 Inventor Gary Dan Dotson Muskego WI US 73 Assignee Rockwell Automation Technologies Inc Mayfield Heights OH US Notice Subject to any disclaimer the term of this patent is extended or adjusted under 35 U S C 154 b by 512 days 21 Appl No 10 832 668 22 Filed Apr 27 2004 65 Prior Publication Data US 2004 0196269 A1 Oct 7 2004 Related U S Application Data 63 Continuation of application No 09 677 103 filed on Sep 29 2000 now Pat No 6 753 853 51 Int CI G09G 5 00 2006 01 52 UIS CL 345 174 178 18 01 178 18 02 178 20 01 58 Field of Classification Search 345 173 179 178 18 01 18 07 19 01 19 04 20 01 20 04 See application file complete search history 56 References Cited U S PATENT DOCUMENTS 4 413 314 11 1983 Slater et al Continued FOREIGN PATENT DOCUMENTS WO WO9 49650 11 1998 OTHER PUBLICATIONS Prentice Hall s Illustrated Dictionary of Computing 2nd Ed 1985 p 59 Continued Primary Examiner Henry Tran 74 Attorney Agent or Firm Himanshu S Amin Alexander M Gerasimow 57 ABSTRACT A method of determining a type of touch plane operator input device comprises sensing the impedance across first and second terminals of a t
18. al 120 can receive the 5 power supply input either directly SW11 or by way of a pull up resistor SW22 With the pull up resistor the analog switch matrix 104 can supply the Vp power supply input to an I O terminal of a touch screen in a way that allows the terminal 120 to be pulled low if the touch screen I O terminal is connected to ground either directly or by way of touch screen resistance or to be left high if no connection to ground exists similar arrange ment is provided for the terminal 124 As will be detailed below this is one preferred way of enabling the touch screen interface circuit to distinguish between different types of touch screens 2 Automatic Detection of Touch Screen Type Referring now to FIGS 4A 4B two preferred methods of determining a touch screen type is illustrated The touch screen interface circuit 100 is capable of receiving input data from a variety of types of touch screens and it is desirable US 7 327 354 B2 7 that the touch screen interface circuit 100 be able automati cally determine the touch screen type to which it is con nected This can be accomplished by sensing the impedance characteristics of the touch screen FIGS 4A 4B describe two exemplary methods that can be performed during a boot up seguence of a device that incorporates the interface circuit 100 to determine a touch screen type Referring first to FIG 4A at step 150 it is first deter mined whether a touch scre
19. al scanning algorithms if desired Assuming the microprocessor 86 does not directly control the A D converter 102 and the analog switch matrix 104 then the responsibilities of the microprocessor 86 in the scanning process are simply to load all of the setup registers for the touch array scanning and enable the state machine 251 during initialization and then respond to incoming event notifications during normal operation The logic circuit 250 is preferably responsible for scanning the touch screen and acguiring data samples verifying that the deviation in the sample set is less than a predetermined amount averaging the samples to determine the X and Y locations of the touch verifying that any movement in the touch location is not so large as to be unrealistic and verifying that any movement is large enough to issue an event notification to the micro processor 86 For all touch screen types the touch screen X and Y axis positioning are preferably linear so that all algorithms de scribed below have linear operation characteristics In other words the voltage that is sampled by the A D converter 102 is preferably linearly related to the X position or the Y po sition of the touch depending on which axis is being scanned Thus a minimum sample voltage corresponds to a minimum position along the X axis a maximum sample voltage corresponds to a maximum position along the X axis and there is a linear relationship between voltage and positi
20. an inverting logic gate 106 The analog to digital converter 102 may be implemented using virtually any A D conversion technigue In the illustrated embodiment the A D converter 102 is a successive approximation A D converter or a delta sigma A D converter The analog switch matrix 104 comprises twenty eight analog switches labeled SW0 SW27 The configuration of the switch matrix 104 is controlled by a plurality of registers including a DIRECT register 110 a DETECT register 112 a DISCHARGE register 114 an XSAMPLE register 116 and a YSAMPLE register 118 Additional registers may also be utilized if it is desired to achieve additional functionality using the analog switch matrix 104 The registers 110 118 control the configuration of the analog switch matrix The configuration of the switch matrix 104 as shown in FIG 3 is characterized by the following bit string 0000 0100 0000 0000 0110 0010 0000 The bits in the foregoing bit string correspond to the open closed states of the switches SW0 SW27 in FIG 3 with the number of the switch 0 27 indicating bit position and a 1 at a particular bit position indicating that a particular switch is closed Different configurations of the analog switch matrix can be obtained with different bit strings These bit strings may be stored in the registers 110 118 or alternatively may be provided directly by the microprocessor As will be described in greater detail below each register controls 2
21. ant voltage is applied to the V and terminals 56 57 The X and Y axes are scanned by applying a voltage at the Z Z and Z Z terminals 58 59 and then reversing the polarity of the voltage to scan the other direction The resulting two voltages produced at the wiper terminal 60 are indicative of the X and Y positions of the touch FIG 1D is a schematic diagram of a 7 wire analog resistive touch screen The 7 wire touch screen is the same as the 5 wire touch screen except that two additional sV and feedback terminals 61 62 are provided As with the sX 57 and sY feedback terminals 40 43 the sV and sV feedback terminals 61 62 are used for voltage feedback to eliminate the effects of resistance and tempera ture drift in the circuit components Analog resistive touch screens are popular because they are inexpensive and reliable However other types of touch screens are also common such as capacitive touch screens and electrostatic touch screens In view of these different types of touch screens a touch screen interface that is compatible with these multiple different types of touch screens would be highly advanta geous A touch screen interface that is capable of automati cally detecting the type of touch screen to which it is connected would also be highly desirable Another problem that has been encountered in connection with touch screens is the processing overhead required to process information from touch s
22. ay all be true because the contact resistance is usually fairly high compared to the indium tin oxide layer resistance As a result a determination can be made whether a 4 wire touch screen or a 5 wire touch screen is connected based on the relative impedance comparisons set forth above Regardless whether a 4 wire or 5 wire touch screen is connected the process proceeds to step 154 where it is determined whether the touch screen is operating properly After that at step 156 it is determined whether the touch screen is pressed The following table summarizes the operation of the analog switch matrix 104 during steps 154 156 for a 4 wire touch screen US 7 327 354 B2 11 REGIS STEP TER EFFECT TEST RESULT 154 0401601 Pull X high Short Check that X Operational X to VSS is low 154 0804604 Pull Y high Short check that Y Operational Y to VSS is low 154 0402601 Pull X high Short ADC Low touch Y to VSS conversionon screen pressed or shorted High No touch screen press The following table summarizes the operation of the analog switch matrix 104 during steps 154 156 for a 5 wire touch screen 154 0401601 Pull X high Short check that X Operational X to VSS is low 154 0402601 Pull X high Short check that X Operational to VSS is low 154 0404601 Pull X high Short check that X Operational Y to VSS is low 156 0420601 Pull X high Short ADC Low touch sY to VSS conversion on screen pressed or
23. ce circuit 100 including an analog switch matrix 104 digital signal processor commu nication network interface display interface and so on see FIGS 2 3 and 7 As previously discussed the analog switch matrix 104 is coupled to the touch screen sensor system and has a plurality of different configurations The analog switch matrix receives power supply inputs V pp Vss and selec tively supplies these input to the touch screen sensor system based on the configuration of the analog switch matrix 104 The digital signal processor determines the touch screen type based on the response of the touch screen to the input in the plurality of different configurations of the analog switch matrix for example as discussed in connection with FIGS 4 and 5A 5D The digital signal processor can also process the input data samples from the touch screen for example as discussed above in connection with FIGS 6 7 In addition to the applications illustrated in FIG 10 and FIG 11 numerous additional applications are also possible For example the integrated circuit 70 can be used in connection with personal digital assistants and other palm held computers as well as internet access devices laptop computers point of sale terminals input only touch pads for larger displays or virtual headsets consumer appliances entertainment systems and other commercial and industrial applications Indeed in FIG 10 the operator interface 300 may be coupled to
24. comparator 278 compares the differ ence to the value XDEV provided by a deviation register 280 by way of a multiplexor 282 If the range exceeds the deviation allowed the results are disregarded and the logic circuit 250 starts over with initialization and generating a new X sample set At step 208 it is determined whether an XINT flag 1 set On the initial pass through the process of FIG 6 the XINT flag is not set and the process proceeds to step 210 As will become apparent this flag is set when the process proceeds from step 210 to step 212 allowing step 210 to be skipped thereafter At step 210 a comparison is made between the new X average sample value X that is the average X sample value determined in step 204 and the last valid X average US 7 327 354 B2 19 sample value XLAST that is the average X sample determined during the previous successful iteration of step 204 Specifically the difference X XLAST between these two values is compared against the XMIN value stored in the XMIN register 290 In FIG 7 this step is performed by providing the output of the tap circuit 267 to the subtractor circuit 274 by way of the multiplexor 272 and by providing the value stored in the LAST X register 286 to the subtractor circuit 274 by way of the multiplexor 270 The output of the subtractor circuit 274 is then provided to the comparator 278 by way of the multiplexor 282 The comparator 278 com pares the difference to the
25. creens It is known to emulate a hardware mouse by moving a mouse pointer across a touch screen in response to an operator touch that moves across the touch screen It is desirable to have smooth and responsive mouse pointer movement Current tech niques for obtaining a satisfactory level of responsiveness require a significant amount of processor overhead how ever because the microprocessor scans the touch screen directly or because the microprocessor must monitor a continuous stream of data from a separate scanning module or hardware For example dragging a cursor around the screen in random directions on a Microsoft amp WindowsTM NT system that supports hardware cursoring can register an additional 3 to 7 of the processing power of a 300 MHz Pentium IITM system under the task monitor program By comparison major architectural or processor step changes usually provide only a 5 to 1096 processing speed improvement A touch screen interface that reduces the amount of microprocessor overhead required for hardware mouse emulation would be advantageous This is especially important in embedded solutions and PDAs where high power processors are less cost effective Therefore a touch screen interface that minimizes process or overhead would also be highly advantageous especially if it is capable of detecting the type of touch screen to which it is detected and or is compatible with multiple different types of touch screens Another ongoing c
26. croprocessor 86 in the scanning process is minimized FIG 7 is a block diagram of a logic circuit 250 that is used to implement the computational aspects of the process embodied in the flowchart of FIG 6 The logic circuit 250 is part of the touch screen interface circuit 100 The logic circuit 250 preferably performs all sampling averaging and range checking for samples acquired by the A D converter 102 from the touch screen sensor circuitry The sequential aspects of the process of FIG 6 are implemented in a state machine 251 In addition to controlling the overall sequence of operations in FIG 7 the state machine 251 is also used to program the analog switch matrix with values from the registers 112 118 as the process proceeds The individual states of the state machine 251 track the steps of the flow chart of FIG 6 and therefore are not separately shown In this regard it may be noted that a circuit layout for the entire discrete logic circuit 250 including the state machine 251 may be generated using a hardware description language 10 20 25 30 35 40 45 50 55 60 65 16 HDL such as verilog of VHDL VHASIC Very High level ASIC Hardware Description Language If desired provision may also be made to disable the touch screen circuitry of FIG 7 and allow the microproces sor 86 to directly control the A D converter 102 and the analog switch matrix 104 This allows for the implementa tion of addition
27. describes the X position of the touch At step 206 it is determined whether the difference between the maximum and minimum X samples is less than a predetermined maximum deviation In other words as previously mentioned all of the acquired samples should indicate that the touch occurred at approximately the same location on the touch screen otherwise the data set as a whole is suspect and should be discarded This range check ing function allows a data set to be screened for erroneous data points possibly caused by noise that would adversely affect an average value It may be noted that when the analog switch matrix 104 is in the configuration shown in FIG 84A relatively little power is dissipated as compared to when the analog switch matrix 104 is in a configuration usable for scanning as in FIGS 8C and 8D discussed below When the switch matrix is in a scanning configuration current flows to the X axis and Y axis resistive layers i e in the case of a 4 wire or 8 wire touch screen Specifically an initial current flows when the scanning voltage is first applied causing a charge to be established on the X axis and Y axis resistive layers which in combination initially behave as a capacitor Once the charge is established current also flows from the bus bar to the X bus bar when a scanning signal is applied to scan the X axis and from the Y 4 bus bar to the Y bus bar when a scanning signal is applied to scan the Y axis
28. e touch screen is connected then the terminal 120 is pulled low because the only touch screen types that have sX and sX connected are the 7 wire and 8 wire touch screens and the 8 wire touch screen has already been eliminated As a result when the switch matrix 104 15 configured as shown in FIG 5C the voltage at the terminal 120 can be measured using the A D converter 102 to determine whether an 7 wire touch screen is connected If a 7 wire touch screen is connected then the process proceeds to step 154 where it is determined whether the touch screen is operating properly The various configura tions for the analog switch matrix 104 are set forth in the table above If all the conditions in the table are met then the touch screen is operating properly otherwise the touch screen is not operating properly Next at step 156 it is determined whether the touch screen is pressed To perform this test the X terminal 120 is pulled high and the wiper terminal 132 is connected to the ground terminal and it is determined whether the X terminal 120 is high or low 1 whether the X axis layer is touching the wiper layer If the terminal 120 is low then the touch screen is pressed although an alternative reason may be that the touch screen is shorted If the terminal 120 is high then the touch screen is not pressed If it is determined at step 158 that an 7 wire touch screen is not connected to the interface circuit
29. en is connected to the interface circuit 100 FIG 5A shows the configuration of the analog switch matrix 104 during step 150 The following table summarizes the operation of the analog switch matrix 104 during step 150 STEP REGISTER EFFECT TEST RESULT 150 047F601 Pull X high Short ADC Low Touch Y sX conversion screen SX sY sY to on X connected VSS High No touch screen connected The value stored in the DIRECT register 110 which changes throughout the processes of FIGS 4A 4B controls the configuration of the analog switch matrix 104 during the processes of FIGS 4A 4B The value stored in the DIRECT register 110 during step 150 is 047F601 hexadecimal or 0000 0100 0111 1111 0110 0000 0001 binary When the analog switch matrix 104 is programmed with this value the effect is to pull X high and to short the X Y Y sX sX sY and sY terminals 122 134 to V ss as described in the table The A D converter 102 then performs an A D conversion on the X terminal 120 If a touch screen is connected then the touch screen establishes a connection between the X and X terminals 120 and 122 i e in the case of a 4 wire or 8 wire touch screen or the V and V terminals in the case of a 5 wire or 7 wire touch screen causing the terminal to be pulled low If no touch screen is connected then no connection is established between the and terminals 120 and 122 and the terminal 120 remains pul
30. erface 300 is provided with a system on chip integrated circuit 70 The integrated circuit 70 therefore includes the circuitry discussed above in connection with the preferred touch screen interface circuit 100 including an analog switch matrix 104 digital signal processor commu nication network interface display interface and so on see FIGS 2 3 and 7 As previously discussed the analog switch matrix 104 is coupled to the touch screen sensor system and has a plurality of different configurations The analog switch matrix receives power supply inputs V pp V ss and selec tively supplies these input to the touch screen sensor system based on the configuration of the analog switch matrix 104 The digital signal processor determines the touch screen type based on the response of the touch screen to the input in the plurality of different configurations of the analog switch matrix for example as discussed in connection with FIGS 4 and 5A 5D The digital signal processor can also process the input data samples from the touch screen for example as discussed above in connection with FIGS 6 7 Referring now to FIG 11 FIG 11 illustrates the system on chip integrated circuit 70 employed in an operator inter face 400 that may also be used as a soft controller in the industrial control system In addition to the operator inter face the industrial control system also comprises a plurality of input and output devices 401 and multiple data
31. es a touch screen interface circuit 100 in accordance with a preferred embodiment of the present invention The integrated circuit 70 includes a plurality of devices that are disposed on a peripheral bus 72 including one or more universal asynchronous receiver transmitters UARTs 73 one or more serial interfaces 74 for interfacing to external devices such as digital to analog converters DACs audio controllers and so on interrupt controller timers 75 a keypad interface 76 one or more I O ports 77 and a touch screen interface circuit 100 described in greater detail below The integrated circuit 70 also includes a plurality of devices that are disposed on a processor bus 80 including one or more universal serial bus USB host interfaces 81 for connection to USB devices such as a keyboard mouse printer and so on an Ethernet port 82 DMA controllers 83 a microprocessor 86 a display interface 87 for example a raster engine memory controllers such as a SRAM and flash interface 88 and a SDRAM interface 90 and boot ROM 89 for storing program code executed during a boot up seguence Referring now to FIG 3 a portion of the preferred touch screen interface circuit 100 of FIG 2 is illustrated in greater detail The remainder of the preferred interface circuit is shown in FIG 7 discussed in greater detail below In FIG 3 the interface circuit 100 comprises an analog to digital A D converter 102 an analog switch matrix 104 and
32. fference exceeds the predetermined amount According to yet another aspect of the invention the invention relates to an interface circuit for a touch plane operator input device the interface circuit comprising a digital signal processor that includes a data processing path along which data from a touch plane operator input device passes while being processed by the digital signal processor The interface circuit is capable of processing data from at least first and second different types of touch plane operator input devices The data path is a common data processing path that is the same for input data regardless of which type of touch plane operator input device is used According to yet another aspect of the invention the invention relates to a system that automatically configures a touch screen interface for one of a plurality of touch screen types The system comprises a first component that utilizes touch screen power signals to automatically determine a type of touch screen coupled to the interface and a second component that configures the interface by writing values associated with the touch screen type to memory accessible to the interface The first component comprises an analog to digital converter an analog switch matrix and at least one register The second component comprises a microproces sor BRIEF DESCRIPTION OF THE DRAWINGS FIGS 1A 1D are schematic diagrams of analog resistive touch screens appropriately labeled
33. hallenge that has been encountered is trying to reduce power consumption to extend battery life in devices such as personal digital assistants laptop computers portable internet access devices and so on A touch screen interface that decreases power consumption would therefore be highly advantageous 20 25 30 35 40 45 50 55 60 65 4 SUMMARY OF THE INVENTION According to one aspect of the invention the invention relates to a method of determining a type of a touch plane operator input device comprising sensing the impedance across first and second terminals of a touch plane operator input device to distinguish the touch screen as being one of at least two different types of touch plane operator input devices According to another aspect of the invention the inven tion relates to a method of processing an input from a touch plane operator input device comprising determining a first location of a first touch on the touch plane operator input device determining a second location of a second touch on the touch plane operator input device comparing the first and second locations to obtain an indication of an amount of difference between the first and second locations and deter mining whether the indication of the amount of difference exceeds a predetermined amount These steps are performed by discrete logic circuitry that provides an event notification to a microprocessor when the indication of the amount of di
34. led high The terminal 120 is also connected to the input of the A D converter 102 and therefore the voltage at the terminal 120 can be measured using the A D converter 102 to determine whether a touch screen is connected If no touch screen is connected then the auto detect process terminates and for example the user may be notified that no touch screen has been detected Assuming a touch screen is connected it is next deter mined at step 152 whether an 8 wire touch screen is con nected or whether another type of touch screen is connected FIG 5B shows the configuration of the analog switch matrix 104 during step 152 The following table summarizes the operation of the analog switch matrix 104 during steps 152 156 STEP REGISTER EFFECT TEST RESULT 152 0840604 Pull Y high Short ADC High sY to VSS conversion on Other type of touch screen connected 20 25 30 35 40 45 50 55 60 65 8 continued STEP REGISTER EFFECT TEST RESULT Low 8 wire touch screen connected 154 0401601 Pull X high Short check that X Operational X to VSS is low 154 0408601 Pull X high Short check that X Operational to VSS is low 154 0410601 Pull X high Short check that X Operational sX to VSS is low 154 0804604 Pull Y high Short check that Y Operational Y to VSS is low 154 0820604 Pull Y high Short check that Y Operational to VSS is low 156 0402601 Pull X high Shor
35. lizes the values associated with the touch screen type to determine when the touch screen is pressed 6 The system of claim 1 the first component determines the type of touch screen based on at least one of an impedance and a capacitance 7 The system of claim 1 the touch screen type is one of a 4 wire 5 wire 7 wire and 8 wire touch screen 8 The system of claim 1 is employed in connection with a device during boot up to automatically configure the device to use the touch screen 9 The system of claim 1 the first component further comprises an inverter 10 The system of claim 1 the analog to digital converter employs one of a successive approximation and a delta sigma technigue 11 The system of claim 1 the at least one register stores information that is utilized to control the switch matrix 12 The system of claim 1 is implemented in a system on chip integrated circuit 13 The system of claim 1 the touch screen comprises at least two resistive layers 14 A method for automatically configuring a touch screen interface for a touch screen coupled to a device comprising sensing a touch screen is coupled to the interface performing an analysis using information associated with a plurality of terminals of the touch screen _ 0 WR 5 25 24 utilizing the analysis to determine a type of touch screen and automatically configuring the interface for the type of touch screen 15 The method of claim 1
36. new samples are acquired the new samples are compared with the values stored in the MIN and MAX sample registers 252 and 254 and after all of the samples have been acquired the minimum sample will be stored in the MIN sample register 252 and the maximum sample will be stored in the MAX sample register 254 In addition to determining the minimum and maximum sample values the circuitry also determines an average sample value To this end as the samples are acquired the samples are also provided to an adder 264 which cooperates with an accumulate and shift register circuit 266 The accumulate and shift register 266 which is initially set equal to zero adds each sample to the previously acquired samples When all of the samples have been acquired the accumulate and shift register 266 outputs a value that is equal to the summation of all acquired samples The result ing value is shifted by 2 3 4 or 5 places to divide by the number of samples This is achieved using the tap circuit 267 which receives a 17 bit input and outputs only the twelve most significant bits 1 for division by 32 In other words if thirty two i e 27 samples are acquired then discarding the first five bits of the output of the accumulate and shift register 266 effectively divides the output of the register 266 by thirty two and produces an average sample 40 45 50 65 18 value The average sample value is then considered to be the value that
37. nterval and that the key press is invalid However at step 214 the new X value is stored as the LAST X register that is XLAST is set equal to X in case a truly new location was determined The XINT flag is also set to cause the algorithm to skip step 210 on consecutive sample sets This flag will also cause a proces sor interrupt after valid X and Y samples have been estab lished The algorithm then starts over discharging and sampling a new X axis value If the difference in step 212 is less than the XMAX then the process proceeds to step 216 At step 216 just as in step 214 the new X value is stored as the LAST X register that is XLAST 1 set equal to X and the XINT flag is also set to cause the algorithm to skip step 210 on consecutive sample sets After step 216 unlike after step 214 the process then proceeds to step 224 where scanning of the Y axis begins In the exemplary process of FIG 6 both the XINT flag and the YINT flag must be set in order for an event notification such as a hardware interrupt to be issued to the microprocessor 86 Except to the extent that a different axis is scanned scanning of the Y axis is identical to the scanning of the X axis and therefore the process will be described more briefly The circuitry in FIG 7 is used as previously described except that registers 294 296 and 298 are used instead of registers 286 290 and 298 respectively Scanning of the Y axis begins at step 224 FIG 8D
38. o SJOoul 9 si llonuoo jdnueju pue via WON joog 06 eoepelul USE J 9 INVHS 98 JosseooudoJo N Old SOH asn lenas LJ lt U S Patent Feb 5 2008 Sheet 3 of 11 US 7 327 354 B2 100 106 720 TOUCH PRESS 112 Wer a salt SW13 102 4 120 X or V or V 5 Ed Y or 24 126 TW SW44 SW4 i Xt or sve ger SX v gg s 5025 sY AE SW27 5 U S Patent Feb 5 2008 Sheet 4 of 11 US 7 327 354 B2 Touch screen connected 152 8 wire touch screen connected 5 wire touch screen connected Touch screen pressed FIG 4A U S Patent Feb 5 2008 Sheet 5 of 11 US 7 327 354 B2 172 Touch screen connected 174 176 4 wire touch screen connected 4 wire or 8 wire touch screen connected 180 5 wire or 7 wire touch screen connected 182 5 wire touch screen connected ouch screen operating properly 7 wire touch screen connected 180 Touch screen pressed FIG 4B 0 7 327 354 2 Sheet 6 of 11 Feb 5 2008 U S Patent ld US 814 Nili 33183ANOO U d XX 1 u U3LH3JANOO NARE
39. on between these two extremes For 8 wire and 4 wire touch screens this is normally the case by virtue of the manner in which these touch screens are constructed Most 5 wire and 7 wire touch screens are constructed with pro prietary compensation techniques and are sufficiently close to linear to produce acceptable results For those that pro duce non linear results the returned values can be adjusted in firmware in conventional fashion to determine screen position The process begins at a touch detect step 202 in which the system waits for a touch press The switches SW0 SW27 in the touch detect step 202 are controlled by the value in the DETECT register 112 The configuration of the analog switch matrix in step 202 for a 4 wire touch screen is shown in FIG 8A The touch press signal is generated at the output ofthe inverting logic gate 106 The process stays at the touch detect step 202 until a touch is detected at which point the process to the next step At step 204 the X axis is scanned The first step to scanning the X axis is to discharge the touch screen wait for a predetermined settling time to elapse apply a voltage to scan the X axis and then wait for another predetermined settling time to elapse This sequence of events allows any residual voltage in the touch screen sensor circuitry to be discharged and for the touch screen sensor circuitry to reach stable operating conditions after a scanning voltage is applied and bef
40. ore samples are acquired FIG 8B shows the configuration of the analog switch matrix 104 for a 4 wire touch screen to discharge the touch screen sensor circuitry FIG 8C shows the configuration of the analog switch matrix 104 for a 4 wire touch screen to apply a voltage to the touch Screen sensor circuitry to scan the X axis The A D converter 102 begins acquiring samples after the scanning voltage is applied and after the touch screen sensor circuitry reaches stable operating conditions To allow a US 7 327 354 B2 17 simple division to be implemented as described below the number of samples taken is preferably either 4 8 16 or 32 Each sample is a voltage sample acguired from the bus bar e g if a 4 wire touch screen is being scanned How ever since voltage and position are linearly related as previously described each sample also represents a particu lar X position on the screen Ideally the samples should be very close together that is the deviation should be small if they are not the sample set is discarded as described below As the samples are acguired during step 204 the maxi mum sample value the minimum sample value and an average sample value are determined and stored As previ ously mentioned the calculations described in the flowchart of FIG 6 are performed by the discrete logic circuitry of FIG 7 As shown therein the A D converter 102 samples the analog voltages acguired via the analog switch mat
41. ort Check High to VSS Short Touch Detect Operational and X4 bit ogether 78 0840005 Pull Y high Short Check High sY to VSS Short Touch Detect Operational Y and X4 bit ogether 80 0402000 Pull X high Short Check High touch Y to VSS Touch Detect screen pressed bit or shorted Low No touch screen press If it is determined at step 174 that a 5 wire or 7 wire touch screen 15 connected instead of a 4 wire an 8 wire touch screen then the process proceeds to step 182 where it 15 determined whether a 5 wire touch screen is connected or whether an 7 wire touch screen is connected The following table summarizes the operation of the analog switch matrix 104 during step 182 REGIS STEP TER EFFECT TEST RESULT 182 0408000 Pull X high Short Check Low 5 wire sX to VSS Touch Detect touch screen bit connected High 7 wire touch screen connected 5 wire with feedback Regardless whether a 5 wire touch screen or an 7 wire touch screen is connected the process proceeds to steps 178 and 180 where it 15 determined whether the touch screen is operating properly and whether the touch screen 1 pressed The following table summarizes the operation of the analog switch matrix 104 during step 178 180 for a 5 wire touch screen STEP REGISTER EFFECT TEST RESULT 178 0401000 Pull X high Short Check High X to VSS Touch Detect Operational bit 20 25 30 35 40 45 55 60
42. ouch plane operator input device to distinguish the touch plane operator input device as being one of at least two different types of touch plane operator input devices A method of processing an input from a touch plane operator input device comprises determining a first location of a first touch on the touch plane operator input device determining a second location of a second touch on the touch plane operator input device comparing the first and second locations to obtain an indication of an amount of difference between the first and second locations and deter mining whether the indication of the amount of difference exceeds a predetermined amount These steps are performed by discrete logic circuitry that provides an event notification to a microprocessor when the indication of the amount of difference exceeds the predetermined amount An interface circuit for a touch plane operator input device comprises a digital signal processor that includes a data processing path along which data from a touch plane operator input device passes while being processed by the digital signal processor The interface circuit is capable of processing data from first and second different types of touch plane operator input devices The data path is a common data processing path that is the same for input data for both of the first and second types of touch plane operator input devices 20 Claims 11 Drawing Sheets 0 7 327 354 2 Page 2 U S PATENT
43. ouch screen is connected the process proceeds to steps 178 and 180 where it is determined whether the touch screen is operating properly and whether the touch screen is pressed The following table summarizes the operation of the analog switch matrix 104 during step 178 180 for a 4 wire touch screen REGIS STEP TER EFFECT TEST RESULT 178 0401000 Pull X high Short Check High X to VSS Touch Detect Operational bit 178 0804005 Pull Y high Short Check High Y to VSS Short Touch Detect Operational and bit together 178 0404005 Pull X high Short Check High Y to VSS Short Touch Detect Operational and bit together 180 0402000 Pull X high Short Check High touch Y to VSS Touch _ Detect screen pressed bit or shorted Low No ouch screen press US 7 327 354 B2 13 The following table summarizes the operation of the analog switch matrix 104 during step 178 180 for an 8 wire touch screen REGIS STEP TER EFFECT TEST RESULT 78 0401000 Pull X high Short Check High X to VSS Touch Detect Operational bit 78 0408000 Pull X high Short Check High to VSS Touch Detect Operational bit 78 0410000 Pull X high Short Check High sX to VSS Touch Detect Operational bit 78 0804005 Pull Y high Short Check High Y to VSS Short Touch Detect Operational and X4 bit ogether 78 0820005 Pull Y high Sh
44. prior art FIG 2 is a block diagram of a system on hip integrated circuit that includes a touch screen interface circuit FIG 3 is a schematic diagram of the touch screen inter face circuit of FIG 2 shown in greater detail FIGS 4A 4B are flow charts showing the operation of the touch screen interface circuit of FIG 3 to determine a touch screen type FIGS 5A 5D are schematic diagrams showing the con figuration of the touch screen interface circuit of FIG 3 during different steps of the process of FIG 4 FIG 6 is a flow chart of a scanning process used by the touch screen interface circuit of FIG 3 FIG 7 is a block diagram of a logic circuit that is used to implement the process of FIG 6 FIGS 8A 8D are schematic diagrams showing the con figuration of the touch for a first type of touch screen US 7 327 354 B2 5 FIG 9 is a representation of a minimum move notification system embodied in the flowchart of FIG 6 FIG 10 is a first industrial control system having an operator interface that incorporates the touch screen inter face circuit of FIG 3 and FIG 11 is a second industrial control system having an operator interface that incorporates the touch screen inter face circuit of FIG 3 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 1 Construction of Touch Screen Interface Circuit Referring now to FIG 2 FIG 2 is a block diagram of an example of a system on chip integrated circuit 70 that includ
45. r less whereas other touch screens are much larger e g twenty inches or more The interface characteristics of large 0 20 40 45 50 55 2 touch screens tend to be different because voltage feedback provisions are made to compensate for the effects of resis tance and temperature drift due to the larger screen size Additionally even within the feedback nonfeedback catego ries of touch screens variations exist As a result it has been difficult to provide a system on chip that is usable in a wide variety of touch screen applications because different touch screen applications tend to use different types of touch screens and different types of touch screens have different interface characteristics FIGS 1A 1D below show four different types of com monly employed analog resistive touch screens In general most analog resistive touch screens comprise front and back resistive layers often formed of indium tin oxide that are pressed together when an operator touch is received The operator touch causes the two layers to establish an electrical contact at a particular location on each layer Therefore by applying a voltage to one layer and reading the voltage established by electrical contact on the other layer the location of the touch can be determined based on the known characteristics of each layer For example FIG 1A is a schematic diagram of a 4 wire analog resistive touch screen As shown therein the to
46. reens X and Y axis definitions are arbitrary and different definitions can be coordinated with program code to determine screen position FIG 1B is a schematic diagram of an 8 wire analog resistive touch screen The 8 wire touch screen is the same as the 4 wire touch screen except that four additional 5 sX sY and sY feedback terminals 40 43 are provided Typically both 4 wire touch screens and 8 wire touch screens use an analog to digital converter to sense the voltages that appear at the and terminals In the case of a 4 wire touch screen the reference voltage inputs to the analog to digital converter are connected directly to the same positive and ground terminals of a power supply that also applies voltages to the touch screen In the case of an 8 wire touch screen the reference voltage inputs are con nected to sX and sX terminals 40 and 42 of the X and X bus bars or to sY and sY terminals 41 and 43 of the and Y bus bars respectively The sX sX sY and US 7 327 354 B2 3 sY terminals 40 43 are used voltage feedback to eliminate the effects of resistance and temperature drift in the circuit components FIG 1C is a schematic diagram of a 5 wire analog resistive touch screen The 5 wire analog resistive touch screen includes a resistive layer 52 and a wiper layer 54 The resistive layer includes V Z and Z terminals 56 59 at the four opposing corners of the touch screen const
47. rix 104 see FIG 3 The sample acguired by the A D converter 102 is provided to a MIN sample register 252 a MAX sample register 254 and multiplexors 256 and 258 The MIN register 252 is initialized to a value of 4095 and the MAX register 254 is initialized to a value of zero When the first sample is acguired the first sample is passed to the com parator 260 by the multiplexor 258 At the same time the value in the MIN sample register 252 is passed to the comparator 260 by the multiplexor 256 The comparator 260 compares the first sample to the value in the MIN sample register 252 In the illustrated embodiment the A D con verter 102 is a twelve bit A D converter and therefore the output of the A D converter cannot exceed 4095 Therefore the first sample is lower than the initial value stored in the MIN sample register 252 and the first sample replaces the value stored in the MIN sample register 252 Thereafter the first sample is also provided to the multiplexor 256 and passed to the comparator 260 At the same time the value in the MAX sample register 254 is passed by the multiplexor 258 to the comparator 260 The comparator 260 compares the value stored in the MAX sample register 254 with the first sample Since the MAX sample register 254 is initial ized to zero the first sample is greater than the value stored in the MAX sample register and the first value replaces the value stored in the MAX sample register 254 Thereafter as
48. s iteration of step 204 Spe cifically the difference Y YLAST between these two val ues is compared against a YMIN value If the difference Y YLAST is less than the YMIN value then this indicates that the movement in the Y direction is not significant enough to warrant alerting the microprocessor Therefore the process proceeds to step 236 to determine whether the XINT flag is set If the XINT flag is set then at step 238 the new Y value is stored as the LAST Y register that is YLAST is set equal to Y the microprocessor is notified and the new X and Y values are read by the microprocessor and the XINT and YINT flags are cleared Thereafter the process returns to step 202 and waits for another touch press Otherwise if the XINT flag is not set at step 236 then the process proceeds to step 204 to rescan to X axis If the difference Y YLAST is not less than the YMIN value then this indicates that the movement in the Y direction is significant enough to warrant alerting the micro processor The process in this event proceeds to step 232 where the difference between the new Y value Y and the last Y value YLAST is compared to the YMAX value The purpose of this step is to verify that the distance of Y movement is not so large as to be unrealistic given the short scan time interval If the difference in step 232 is greater than YMAX then at step 234 the new Y value is stored as the LAST Y register that is YLAST is set equal to
49. shows the configuration of the analog switch matrix 104 for a 4 wire touch screen to apply a voltage to the touch screen 20 25 30 35 40 45 50 55 60 65 20 sensor circuitry to scan the Y axis Again 4 8 16 or 32 samples are acquired and the maximum sample value the minimum sample value and an average sample value are determined and stored At step 226 it is determined whether the difference between the maximum and minimum Y samples is less than a predetermined maximum deviation previously described this range checking function allows a data set to be screened for erroneous data points possibly caused by noise that would adversely affect an average value If the range exceeds the deviation allowed the results are disre garded and the logic circuit 250 starts over with initialization and generating a new sample set at step 224 At step 228 it is determined whether a YINT flag is set On the initial pass through the process of FIG 6 the YINT flag is not set and the process proceeds to step 210 The YINT flag serves the same purpose as the XINT flag as described above except that it is used in connection with the Y axis portion of the process of FIG 6 At step 230 a comparison is made between the new Y average sample value Y that is the average Y sample value determined in step 224 and the last valid Y average sample value YLAST that is the average Y sample determined during the previou
50. t ADC Low touch Y to VSS conversionon screen X pressed or shorted High No touch screen press If an 8 wire touch screen is connected then the Y terminal 120 is pulled low because the sY terminal estab lishes a connection to ground For all other touch screen types the sY terminal is unused and therefore the terminal remains high As a result when the switch matrix 104 is configured as shown in FIG 5B the voltage at the terminal 120 can be measured using the A D converter 102 to determine whether an 8 wire touch screen is connected If an 8 wire touch screen is connected then the process proceeds to step 154 where it is determined whether the touch screen is operating properly The various configura tions for the analog switch matrix 104 are set forth in the table above If all the conditions in the table are met then the touch screen is operating properly otherwise the touch screen is not operating properly Next at step 156 it is determined whether the touch screen is pressed This feature may be useful for example to give the operator the option to proceed to a setup screen during a boot up process To perform this test the X4 terminal 120 is pulled high and the Y terminal 124 is connected to the ground terminal and it is determined whether the X terminal 120 is high or low i e whether the X axis layer is touching the Y axis layer If the X terminal 120 is low then the touch screen is pressed al
51. techniques could be used to distin guish between various types of capacitive touch screens and or to distinguish capacitive touch screens from resistive touch screens 3 Touch Screen Data Processing Once a determination has been made regarding the touch screen type to which the interface circuit 100 is connected the interface circuit is configured for the touch screen type that has been determined This is done at least in part by writing various values in the registers 112 118 in accordance with the touch screen type that has been detected The following table shows the values stored in the reg isters 112 118 for each of the four types of touch screens US 7 327 354 B2 15 DETECT DISCHARGE XSAMPLE YSAMPLE 4 wire touch 0402608 007FEOC 00F960C 017C603 screen 5 wire touch 0420620 007FE20 01DD620 02DB620 screen 7 wire touch 0420620 307F820 31DD020 32DB020 Screen 8 wire touch 0402608 007FEOC 308100C C104003 screen The values written in the registers 112 118 customize an otherwise generic scanning process generic in the sense that it can be used with multiple types of touch screens for use with the particular type of touch screen actually connected to the touch screen interface circuit 100 Because the process is otherwise generic it is possible to use a common data processing path regardless of which touch screen type is used FIG 6 is a flowchart that illustrates the preferred scanning process While the process of FIG
52. the internet to permit firmware revisions to be downloaded from a manufacturer of the programmable controller system Many other changes and modifications may be made to the present invention without departing from the spirit thereof The scope of these and other changes will become apparent from the appended claims What is claimed 15 1 A system that automatically configures a touch screen interface for one of a plurality of touch screen types comprising a first component that utilizes touch screen power signals to automatically determine a type of touch screen coupled to the interface the first component compris ing an analog to digital converter an analog switch matrix and at least one register and a second component that configures the interface by writing values associated with the touch screen type to memory accessible to the interface the second com ponent comprising a microprocessor 2 The system of claim 1 the first component further determines whether a touch screen is coupled to the inter face US 7 327 354 B2 23 3 The system of claim 1 the second component writes the configuration to one or more registers including a Detect a Discharge an Xsample and a Y sample register 4 The system of claim 1 the first component further utilizes the values associated with the touch screen type to determine whether the touch screen is operating properly 5 The system of claim 1 the first component further uti
53. though an alternative reason may be that the touch screen is shorted If the X terminal 120 is high then the touch screen is not pressed If it is determined at step 152 that an 8 wire touch screen is not connected to the interface circuit 100 then the process proceeds to step 158 At step 158 it is determined whether a 7 wire touch screen is connected or whether another type of touch screen is connected FIG 5C shows the configu ration of the analog switch matrix 104 during step 158 The following table summarizes the operation of the analog switch matrix 104 during step 158 and steps 154 156 for a 7 wire touch screen REGIS STEP TER EFFECT TEST RESULT 158 0408601 Pull X high Short ADC High Other sX to VSS conversion on type of touch US 7 327 354 B2 9 continued REGIS STEP TER EFFECT TEST RESULT screen connected Low 7 wire touch screen connected 5 wire with feedback 54 0401601 Pull X high Short check that X Operational X to VSS is low 54 0402601 Pull X high Short check that X Operational Y to VSS is low 54 0404601 Pull X high Short check that X Operational Y to VSS is low 54 0408601 Pull X high Short check that X Operational sX to VSS is low 54 0410601 Pull X high Short check that X Operational sX to VSS is low 56 0420601 Pull X high Short ADC Low Touch sY to VSS conversion screen pressed or shorted High No touch screen press If a 7 wir
54. uch screen comprises an X axis resistive layer 12 and a Y axis resistive layer 14 The resistance of the layers 12 and 14 is shown schematically as four resistors The X axis layer 12 further includes an bus bar 16 that connects to an terminal 18 of the touch screen and an bus bar 20 that connects to an X terminal 22 of the touch screen Similarly the Y axis resistive layer further includes a bus bar 26 that connects to a terminal 28 of the touch screen and a Y bus bar 30 that connects to Y terminal 32 of the touch screen The touch screen is scanned in the X direction by applying a voltage across the X and bus bars 16 and 20 and then sensing the voltage that appears at one or both of the and terminals 28 and 32 Assuming negligible current flow through the and terminals the voltage at the and Y terminals 28 and 32 should be approximately the same and is determined by the X coordinate of the point of electrical contact between the X axis and Y axis layers 12 and 14 that is by the X coordinate of the touch By comparing the voltage to values determined during calibra tion the X coordinate of the touch can be determined The Y coordinate of the touch is then determined in the same manner except that a voltage is applied across the and bus bars 26 and 30 and the resultant voltage that appears at one or both of the and X terminals 18 and 22 is sensed Of course with all touch sc
55. used both the X axis and the Y axis and therefore the X terminal 18 and the Y terminal 32 are resistively connected In the case of a 4 wire touch screen the X axis and Y axis layers are different and therefore connecting the Y axis layer to ground will only pull the x axis layer low if the touch screen is being pressed Although this is also true for 8 wire touch screens 8 wire touch screens have already been eliminated in step 152 As a result if the terminal 120 is high then 4 wire touch screen is connected If the terminal 120 is low then a 4 wire screen may be connected and pressed or a 5 wire screen may be connected In this event the remaining configurations of the table above are utilized By using the internal pull up resistors the analog switch array 104 can be configured to perform relative impedance measurements If a 5 wire touch screen is connected the resistance between any two adjacent corners of the touch screen will be less than the resistance diagonally across the touch screen Because of the way X X and Y Y are connected this is exactly opposite of a pressed 4 wire touch screen In a pressed 4 wire touch screen depending on where the press is occur ring the impedance from X to will be greater than X to X X to Y will be greater than X to X Y to X will be greater than to or to X will be greater than to Y One of these OR ed conditions will be true and they m
56. y of applications FIG 10 illustrates the system on chip integrated circuit 70 employed in an operator interface 300 of a legacy configu ration for an industrial control system In addition to the operator interface the industrial control system comprises a plurality of input and output devices 302 a communication network 304 a rack mounted programmable controller sys tem 306 The operator interface 300 could also be used in connection with non rack mounted devices such as soft PLCs In addition to these components the industrial control system may include a wide array of additional components The programmable controller system 306 comprises a control module 308 The control module 308 executes a user program to control output status of the plurality of output devices based on input status information from the plurality of input devices The programmable controller system 306 and the operator interface 300 which may also be rack mounted are coupled to each other by way of the communication network 304 The operator interface 300 includes a touch screen that includes a display 310 and a touch screen sensor system such as shown in FIGS 1A 1D The display 310 displays the input and output status of at least a portion of the plurality of input and output devices 302 The touch screen may for example be a 4 wire 5 wire 7 wire or 8 wire touch screen each of which uses a different sensor system as previously discussed The operator int
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