Manual - Stanford Research Systems
Contents
1. 2 4 Introductions X vs ia PN eR 2 6 2 3 1 Power on configuration 2 6 23 2 BUPEES ss Sse se a be bw ok a ek 2 6 2 3 3 Device Clear aoaaa 2 6 Commands aaas soe Als desi Gd Be DS 2 6 2 4 1 Command y ie de e 2 7 242 Notation y esla a K E be ee ed 2 8 2 4 3 Examples vite Z reed tice ae eer wees 2 8 2 44 Amplifier Commands 2 9 2 4 5 AutocalibrationCommands 2 10 2 4 6 Serial Communication Commands 2 11 2 4 7 Status Commands 2 11 2 4 8 Interface Commands 2 13 Status Model e eee ES 2 17 2 5 1 Status Byte SB 2 18 2 5 2 Service Request Enable SRE 2 19 2 5 3 Standard Event Status ESR 2 19 2 5 4 Standard Event Status Enable ESE 2 19 2 5 5 Communication Error Status CESR 2 20 2 5 6 Communication Error Status Enable CESE 2 20 2 5 7 Overload Status OVCR 2 21 2 5 8 Overload Status OVSR 2 21 2 5 9 Overload Status Enable OVSE 2 21 2 2 Remote Operation 2 1 Index of Common Commands symbol definition ij Integers Z Literal token Required for queries illegal for set commands var parameter always required var required parameter for set commands illegal for queries var optional parameter for both set and query forms Amplifier CHAN i 2 9 Channel Control READ 1 2 9 Read Offset Voltage Autocalibration ARMC z2. SIM980 Analog Summing Amplifier SRS Remote Operation CLS Example Clear Status CLS immediately clears the ESR CESR and OVSR CLS ESR i Example Standard Event Status Reads the Standard Event Status Register bit i Upon executing ESR the returned bit s of the ESR register are cleared ESR 64 ESE 1 4 Example Standard Event Status Enable Set query the Standard Event Status Enable Register bit i to j ESE 6 1 ESE 64 CESR i Example Comm Error Status Query Comm Error Status Register for bit i Upon executing a CESR query the returned bit s of the CESR register are cleared CESR 0 CESE 1 101 Example Comm Error Status Enable Set query Comm Error Status Enable Register for bit i to j CESE 0 OVCR i Example Overload Condition Query Overload Condition Register for bit OVCR 3 ASRS SIM980 Analog Summing Amplifier 2 4 Commands OVSR 1 Example Overload Status Query Overload Status Register for bit Upon executing a OVSR query the returned bit s of the OVSR register are cleared OVSR 0 1 OVSE 1 1 Example Overload Status Enable Set query Overload Status Enable Register bit i to j OVSE 16 PSTA 2 2 4 8 Example Pulse STATUS Mode Set query the Pulse STATUS Mode to Z OFF 0 ON 1 When PSTA ON is set any new serv
3. Signal Src gt Dest Description 1 SIGNAL GND MF gt SIM Ground reference for signal 2 STATUS SIM gt MEF Status service request GND asserted 5 V idle 3 RTS MF gt SIM HW handshake 5 V talk GND stop 4 CTS SIM MF HW handshake 5 V talk GND stop 5 REF_1OMHZ MF gt SIM 10 MHz reference no connection in SIM980 6 5V MF gt SIM Power supply no connection in SIM980 7 15V MF gt SIM Power supply 8 PS KTN MF gt SIM Power supply return 9 CHASSIS GND Chassis ground 10 TXD MF gt SIM Async data start bit 0 5 V 1 GND 11 RXD SIM gt MF Async data start bit 0 5 V 1 GND 12 REF_10MHz MF gt SIM 10 MHz reference no connection in SIM980 13 5V MF gt SIM Power supply 14 15V MF gt SIM Power supply 15 24V MF gt SIM Power supply no connection in SIM980 1 3 2 1 1 3 2 2 Serial settings Table 1 1 SIM Interface Connector Pin Assignments DB 15 Direct interface cabling If the user intends to directly wire the SIM980 independent of the SIM900 Mainframe communication is usually possible by directly connecting the appropriate interface lines from the SIM980 DB 15 plug to the RS 232 serial port of a personal computer Connect RXD from the SIM980 directly to RD on the PC TXD directly to TD and similarly RTS RTS and CIS gt CITS In other words a null modem style cable is not needed To inter
4. symmetric cabling the measurments may be repeated with the inputs being connected to all possible permutations of the four cables Inputs are pairwise set to and such that the overall AC signal is nulled There are twelve possible gain combinations for two channel nulling 0OO0 and 00 0O 0 and O 0 OO and OO O 0 and O O O O and O O OO and OO The combination with the worst common mode rejection is optimized with trimcap C217 and all other combinations are re checked After a few iterations a solution with well distributed error can be found The residual worst case AC voltage will typically be approximately 5mVrms for a 1 Vrms input After completing the adjustments record the results Some users might want to improve DC and AC matching for a single combination of channels e g channels 1 amp 2 while sacrificing the matching for the others This can be accomplished best by driving the two channels with the same signal and operating one in positive and the other one in negative mode while using R268 and C217 to minimize the difference signal at the output Please note that revers ing the polarity of these two channels will not result in an equally well matched result The procedure works within a narrower than specified temperature range and long term drift might make fre quent re calibration necessary 3 5 Other tests and adjustments The SIM980 internally generates two pre
5. 2 10 Arm Autocalibration ACAL 2 10 Perform Offset Autocalibration OFST i tj 2 10 Offset Value Serial Communications FLOW z 2 11 Flow Control PARI z 2 11 Parity Status STB 1 2 11 Status Byte SRE i j 2 11 Service Request Enable CLS 2 12 Clear Status ESR i 2 12 Standard Event Status ESE 1 1 j 2 12 Standard Event Status Enable CESR i 2 12 Comm Error Status CESE i j 2 12 Comm Error Status Enable OVCR i 2 12 Overload Condition OVSR i 2 13 Overload Status OVSE LIU 2 13 Overload Status Enable PSTA z 2 13 Pulse STATUS Mode Interface RST 2 13 Reset IDN 2 14 Identify OPC 2 14 Operation Complete CONS z 2 14 Console Mode LEXE 2 14 Execution Error LCME 2 15 Command Error ASRS SIM980 Analog Summing Amplifier 2 1 Index of Common Commands LBTN TOKN z TERM z 2 15 Button 2 15 Token Mode 2 16 Response Termination SIM980 Analog Summing Amplifier ASRS 2 4 Remote Operation 2 2 Alphabetic List of Commands CLS 2 12 Clear Status ESE 1 1 tj 2 12 Standard Event Status Enable ESR 1 2 12 Standard Event Status IDN 2 14 Identify OPC 2 14 Operation Complete RST 2 13 Reset SRE i tj 2 11 Service Request Enable STB i 2 11 Status Byte A ACAL 2 10 Perform Offset Autocalibration ARMC 2 2 10 Arm Autocalibration C CESE i j 2 12
6. 2 Front Panel Operation The front panel of the SIM980 see Figure 1 1 provides a simple operator interface Figure 1 1 The SIM980 front and rear panels SRS SIM980 Analog Summing Amplifier 1 2 Front Panel Operation 1 3 1 2 1 Inputs Each of the four input channels of the SIM980 has a front panel block consisting of the BNC input connector a control button and several LED indicators 1 2 1 1 Polarity toggle Each input can be switched between inverting or non inverting po larity by briefly pressing that channel s control button When invert ing the LED is illuminated when non inverting is lit Note that the polarity is always displayed independent of whether that channel is on or off 1 2 1 2 On Off toggle Each input can independently be turned on or off by holding that channel s control button for 1 5 seconds When on the channel is either added to or subtracted from the output depending on polarity section 1 2 1 1 When off it does not contribute to the output signal at all The OFF LED is lit to indicate when a channel is off Unused channels should be turned off rather than simply left un connected as the Johnson noise of the open 1 MQ input resistor will dominate the output noise of the SIM980 1 2 1 3 Offset autocalibration The SIM980 uses an active input offset correction to trim all input circuitry as well as the summing circuitry of DC offsets The user can initiate an autocalibr
7. Comm Error Status Enable CESR i 2 12 Comm Error Status CHAN i j 2 9 Channel Control CONS z 2 14 Console Mode F FLOW z 2 11 Flow Control L LBTN 2 15 Button LCME 2 15 Command Error LEXE 2 14 Execution Error O OFST i tj 2 10 Offset Value OVCR i 2 12 Overload Condition OVSE LIU 2 13 Overload Status Enable OVSR i 2 13 Overload Status P PARI z 2 11 Parity PSTA z 2 13 Pulse STATUS Mode R READ i 2 9 Read Offset Voltage ASRS SIM980 Analog Summing Amplifier 2 2 Alphabetic List of Commands T TERM z TOKN z 2 16 Response Termination 2 15 Token Mode SIM980 Analog Summing Amplifier ASRS 2 6 Remote Operation 2 3 Introduction Remote operation of the SIM980 is through a simple command lan guage documented in this chapter Both set and query forms of most commands are supported allowing the user complete control of the summing amplifier from a remote computer either through the SIM900 Mainframe or directly via RS 232 see Section 1 3 2 1 See Table 1 1 for specification of the DB 15 SIM interface connector 2 3 1 Power on configuration 2 3 2 Buffers 2 3 3 Device Clear 2 4 Commands The settings for the remote interface are 9600 baud with no parity and hardware flow control and local echo disabled CONS OFF Most of the SIM980 instrument settings are stored in non volatile memory and at power on the instrument returns to
8. Example In the following all four channels are first commanded off then channels 1 and 2 are turned on the opposite polarities Finally the single channel and four channel queries are shown CHAN 0 0 CHAN 1 1 CHAN 2 1 CHAN 2 1 CHAN 0 1 1 0 0 READ i Read Offset Voltage Query the output voltage in tenths of microvolts When the offset autocalibration circuitry is active an internal high gain amplifier is activated to monitor the SIM980 output This signal is digitized by an internal analog to digital converter The READ query allows the user to directly record this measurement When READ is queried the high gain amplifier is turned on When the query has finished averaging the high gain amplifier is turned off again The optional parameter is the averaging time in milliseconds The valid range is 10 lt lt 10000 with a default value of 1000 1 second The query result is in integer tenths of microvolts That is READ returns Vout X 107 V The total range is roughly 1260 lt READ lt 27650 corresponding to output voltages in the range 1 26 mV through 27 6 mV Example READ 151 SIM980 Analog Summing Amplifier SRS 2 10 Remote Operation 2 4 5 Autocalibration Commands The SIM980 has an internal offset trimming circuit see section 1 2 1 3 The following set of commands provides detailed control over this subsystem ARMC z Example Arm Autocalibration Test
9. K201 K208 A combination of two dual pole dual throw relays per channel allows enable disable and polarity change with constant noise gain and signal bandwidth The difference amplifier U210 is buffered by the power buffer U211 This compound amplifier can drive 10 V signals into open and 5 V into two 50Q loads The outputs on the front and back panel can be used simultaneously with resistive isolation between them The independent 50 Q series resistors at these outputs also guaran tee unlimited stability for any possible passive load and overcur rent thermal protection for shorted outputs The combination of U210 U211 is rolled off at a bandwith of 4MHz by the combintion of C220 and C202 Trim capacitor C217 is factory adjusted for best common mode suppression at high frequencies Outputs as well as inputs are equipped with common mode filters baluns to reduce conducted EMI electromagnetic interference of RF noise currents on the shield of BNC cables attached to the module For the same reason the BNCs are isolated from the SIM980 s front and back panels This design ensures the best DC and low frequency performance in noisy environments Care must be taken not to load the ground connections with currents gt 1 A which could destroy the ASRS SIM980 Analog Summing Amplifier 4 1 Circuit Descriptions 4 3 differential pair wiring inside the module and disconnect the ground from the isolated BNC jacks Such a fault could res
10. amplifier is overloaded output voltage exceeds 10 V Note that the output can overload with out any input channel overloading and vice versa 2 5 8 Overload Status OVSR The Overload Status Register consists of latching event flags that correspond one to one with the bits of the OVCR see above Upon the transition 0 gt 1 of any bit within the OVCR the corresponding bit in the OVSR becomes set Bits in the OVSR are unaffected by the 1 0 transitions in the OVCR and are cleared only by reading or with the CLS command Reading a single bit with the OVSR i query clears only bit i 2 5 9 Overload Status Enable OVSE The OVSE acts as a bitwise AND with the OVSR register to produce the single bit OVSB message in the Status Byte Register SB It can be set and queried with the OVSE command This register is cleared at power on SIM980 Analog Summing Amplifier SRS Remote Operation ASRS SIM980 Analog Summing Amplifier 3 Performance Tests In This Chapter This chapter describes how to adjust the SIM980 to improve its offset and gain accuracy and verify performance 3 1 3 2 3 3 3 4 3 5 3 6 Introduction 3 2 Tools and preparation 3 2 Precalibration Values 3 2 3 3 1 Offset Voltages 20200 400 a as 3 2 3 3 2 Calibration Words 3 3 3 33 DC Gain Match 3 3 3 3 4 AC Gain Match 3
11. and set or query the armed flag for autocalibration If z FORCE 1 the armed flag is set without testing The offset autocalibration proceedure requires that all inputs to the SIM980 be at OV that is either open or shorted to ground The ARMC command performs a test of all 4 channels to ensure that each input is less than 500 uV amplitude If all four channels are okay the armed flag is set otherwise it is cleared The entire test takes about 15 seconds to complete If ARMC FORCE is set the armed flag will be set without performing any test of the input channels ARMC ARMC 1 ACAL Example Perform Offset Autocalibration If the armed flag is set see ARMC above an ACAL command will initiate an offset autocalibration cycle The entire process takes be tween 30s and 90s and should ideally be performed only after the SIM980 has been allowed to warm up at least 30 minutes ACAL OPC 1 OFST i tj Offset Value Set query the low level offset trim for channel i to j 0 255 The result of the ACAL command is stored at 6 low level offset trims The OFST allows direct access to these values The input channel specific offset for channels 1 through 4 are stored in i 1 through 4 respectively For these settings increasing j causes the input offset adjust to decrease by about 6 uV per count i 5 and 6 both adjust the summing node offset voltage Increasing j for i 5 causes the output voltage to dec
12. the corresponding enable registers 1 but see the PSTA command ASRS SIM980 Analog Summing Amplifier 2 5 Status Model 2 5 2 Service Request Enable SRE Each bit in the SRE corresponds one to one with a bit in the SB register and acts as a bitwise AND of the SB flags to generate the MSS bit in the SB and the STATUS signal Bit 6 of the SRE is undefined setting it has no effect and reading it always returns 0 This register is set and queried with the SRE command This register is cleared at power on 2 5 3 Standard Event Status ESR The Standard Event Status register consists of 8 event flags These event flags are all sticky bits that are set by the corresponding event and cleared only by reading or with the CLS command Reading a single bit with the ESR i query clears only bit i Weight Bit Flag 1 0 OPC 2 1 INP 4 2 OYE 8 3 DDE 16 4 EXE 32 5 CME 64 6 URO 128 7 PON OPC INP OYE DDE EXE CME URQ PON Operation Complete Set by the OPC command Input Buffer Error Indicates data has been discarded from the Input Buffer Query Error Indicates data in the Output Queue has been lost Device Dependent Error This bit is undefined in the SIM980 Execution Error Indicates an error in a command that was successfully parsed Out of range parameters are an example The error code can be queried with LEXE Command Error Indicates a parser d
13. the state it was last in when power was removed Exceptions are noted in the com mand descriptions Reset values of parameters are shown in boldface Incoming data from the host interface is stored in a 64 byte input buffer Characters accumulate in the input buffer until a command terminator either CR or LF is received at which point the mes sage is parsed and executed Query responses from the SIM980 are buffered in a 64 byte output queue If the input buffer overflows then all data in both the input buffer and the output queue are discarded and an error is recorded in the CESR and ESR status registers The SIM980 host interface can be asynchronously reset to its power on configuration by sending an RS 232 style break signal From the SIM900 Mainframe this is accomplished with the SIM900 SRST command if directly interfacing via RS 232 then use a serial break signal After receiving the Device Clear the interface is reset and CONS mode is turned OFF Note that this only resets the communi cation interface the basic function of the SIM980 is left unchanged to reset the instrument see RST This section provides syntax and operational descriptions for reo mote commands ASRS SIM980 Analog Summing Amplifier 2 4 Commands 2 4 1 Command Syntax tokens The four letter mnemonic shown in CAPS in each command se quence specifies the command The rest of the sequence consists of parameters Command
14. 2 2K D103 D104 D205 D207 3 00649 BAW56LT1 R250 R251 R253 R254 4 01486 2 0K D201 D204 3 00896 BAV99 R266 4 01541 390k D301 D308 3 00424 GREEN R268 4 00901 500K D309 D313 3 00425 RED R289 R290 4 01561 2 7M D314 D317 3 00426 YELLOW R401 4 01402 931K D401 3 01384 MMBZ5232BLT1 R402 R405 4 00014 5K J101 1 00367 15 Pin D R403 4 01308 97 6K J103 1 00302 Socket 0 100 3x2 R404 4 01310 102K J201 J206 1 00003 BNC R406 4 01348 255K JS201 1 01079 20 pin R407 4 01526 91K JS301 1 01080 20Pin R408 4 01517 39K K201 K208 3 01492 ASX2204H R415 R420 4 01524 75K L101 L102 L103 6 00174 FR43 Bead R425 R428 4 01499 6 8K L201 L206 6 00640 ToroidChoke R431 4 00925 10 Q101 Q116 3 01421 MMBT2222A RN200 RN201 4 01649 1 000K Q201 Q206 3 00580 MMBT3906LT1 RN301 RN302 4 00442 1 2K 1206 mini QN201 3 01419 MBT3906DW1 S301 S304 2 00053 B3F 1052 R101 R118 119 R122 4 01527 100k U101 3 01379 68HC912B32 R123 R213 216 R240 U102 3 00903 MAX6348 4 4V R242 243 R260 U103 3 00742 74HC74 R102 R201 R203 R205 4 01479 1 0k U104 3 00662 74HC14 R207 R221 R224 R227 U105 3 01405 74AC00 R230 R291 R423 U106 3 00663 74HC08 R103 4 01052 210 U107 U108 3 00746 74HC245 R104 R217 R220 R241 4 01495 4 7k U201 U204 3 01246 AD8610AR R261 U205 U209 3 00728 LM393 R105 R295 R296 R298 4 01511 22k U210 3 01278 AD829AR R299 R2101 U211 3 01247 BUF634F R106 R262 R263 4 01431 10 U212 3 00998 OPA277UA R107 R110 R115 4 01519 47K U401 3 01415 LP2951CMM R112 R113 R421 R422 4 01551 1 0
15. 3 Calibration Ces seernes eb ae ae a N a a 3 4 3 4 1 Offset Adjustment 3 4 3 4 2 DC Gain Calibration 3 5 3 4 3 AC Gain Calibration 3 5 Other tests and adjustments 3 6 SIM980 Performance Test Record 3 7 3 2 Performance Tests 3 1 Introduction Under typical usage only the internal autocalibration cycle is needed to keep the SIM980 operating within specifications see sec tion 1 2 1 3 If further adjustment is needed this section describes the procedure 3 2 Tools and preparation The necessary tools for a complete recalibration are e asmall flat head screwdriver e a voltmeter with microvolt resolution and stability SIM970 or equivalent a quiet DC voltage source SIM928 or equivalent a 1 MHz minimum sine generator DS345 or equivalent e a 20 MHz bandwidth minimum oscilloscope e several BNC patch cables e 4 BNC Tee adapters or 3 Tees and 1 F F barrel For the full offset calibration procedure the module should be run ning for at least 15 minute The trimpots are accessible after removing the right side panel It is easier to calibrate the module by connecting it through a cable to the SIM extension port but the calibration can also be performed with the module located in the left most slot slot 1 of a SIM900 Mainframe with slots 2 5 empty 3 3 Precalibration Values 3 3 1 Offset Voltages If precalibration values are not required sk
16. Analog Summing Amplifier SRS 2 8 Remote Operation 2 4 2 Notation 2 4 3 Examples The following table summarizes the notation used in the command descriptions symbol definition ij Integers Z Literal token Required for queries illegal for set commands var parameter always required var required parameter for set commands illegal for queries var optional parameter for both set and query forms Each command is provided with a simple example illustrating its usage In these examples all data sent by the host computer to the SIM980 are set as straight teletype font while responses received the host computer from the SIM980 are set as slanted teletype font The usage examples vary with respect to set query optional param eters and token formats These examples are not exhaustive but are intended to provide a convenient starting point for user program ming ASRS SIM980 Analog Summing Amplifier 2 4 Commands 2 9 2 4 4 Amplifier Commands CHAN i j Channel Control Set query input channel i to state j 1 0 1 Setting channel i to 0 will turn that channel off Setting j 1 or any positive value less than 32767 turns that channel on and sets the polarity to non inverting Setting j 1 or any negative value greater than 32768 also turns that channel on but sets the polarity to inverting All four channels can be set or queried simultaneously by setting i 9
17. M U402 3 01248 LT1175CN8 R114 R120 R121 4 01503 10K U403 3 01279 MAX5258 R409 R414 R424 U404 3 01280 LTC2050CS5 U405 3 01367 DG419DY ASRS SIM980 Analog Summing Amplifier 4 3 Schematic Diagrams 4 3 Schematic Diagrams Schematic diagrams follow this page SIM980 Analog Summing Amplifier ASRS
18. N The following notation will be used throughout this manual A warning means that injury or death is possible if the instructions are not obeyed A caution means that damage to the instrument or other equipment is possible Typesetting conventions used in this manual are e Front panel buttons are set as Button Adjust AY is shorthand for Adjust 4 amp Adjust 1 e Front panel indicators are set as Overload e Remote command names are set as IDN e Literal text other than command names is set as OFF Remote command examples will all be set in monospaced font In these examples data sent by the host computer to the SIM980 are set as straight teletype font while responses received by the host computer from the SIM980 are set as slanted teletype font SIM980 Analog Summing Amplifier SRS vi General Information Specifications Performance Characteristics Number of inputs Function Gain Input impedance Bandwidth Output voltage noise Crosstalk Offset voltage Input range Output range Input slew rate Total Harmonic Distortion Output slew rate Operating temperature Power General Characteristics Interface 4 Inverting non inverting or off 1x 1 MO DC to 1 MHz 30nV VHz 1 kHz max 80 dB amp 1 kHz 100 uV after 5 min warm up 10 V before overload 10 V before overload 40 V us 0 01 80 dB max 1 kHz 75 V us 0 C to 40 C non condensing 5
19. Operation and Service Manual Analog Summing Amplifier SIM980 SRS Stanford Research Systems Revision 1 8 e May 18 2006 Certification Stanford Research Systems certifies that this product met its published specifications at the time of shipment Warranty This Stanford Research Systems product is warranted against defects in materials and workman ship for a period of one 1 year from the date of shipment Service For warranty service or repair this product must be returned to a Stanford Research Systems authorized service facility Contact Stanford Research Systems or an authorized representative before returning this product for repair Information in this document is subject to change without notice Copyright Stanford Research Systems Inc 2005 2006 All rights reserved Stanford Research Systems Inc 1290 D Reamwood Avenue Sunnyvale CA 94089 USA Phone 408 744 9040 e Fax 408 744 9049 www thinkSRS com e e mail info thinkSRS com Printed in U S A SRS SIM980 Analog Summing Amplifier Contents General Information Symbols Dio RE e Avie amp we ee ee ae ee ates NGATON si a e Aces Ske ae oe Bake A ie Pe Pe a en Specifications cla RE R R ete dale Hid tee ws 1 Getting Started 1 1 Introduction to the Instrument 1 2 Front Panel Operation iaa aaa 1 3 SiMinterface 2 Remote Operation 2 1 Index of Common Commands 2 2 Alphabeti
20. V 100 mA 15 V 300 mA Serial RS 232 through SIM interface Connectors BNC 5 front 1 rear DB 15 male SIM interface Weight 1 5 lbs Dimensions 1 5 W x 3 6 H x 7 0 D ASRS SIM980 Analog Summing Amplifier 1 Getting Started This chapter gives you the necessary information to get started quickly with the SIM980 Summing Amplifier In This Chapter 1 1 Introduction to the Instrument 1 2 LEI COVEIVIEW 3130 a ee ee ed es de 1 2 1 12 Power on State 1 2 1 2 Front Panel Operation 1 2 TZI OPUS cz dd st Mae AA 1 3 12 2 UP a AAA 1 4 1 3 SIM Interface o mce id dede 1 4 1 3 1 SIM interface connector 1 4 1 3 2 Direct interfacing 1 4 1 2 Getting Started 1 1 Introduction to the Instrument The SIM980 Summing Amplifier is a four input unity gain amplifier for combining multiple analog signals from DC to 1 MHz 1 1 1 Overview The basic function of the SIM980 is to add or subtract up to four analog signals Each input channel can be separately configured for inverting or non inverting operation or switched off Each input is 1 MQ and DC coupled and accepts signals between 10 V 1 1 2 Power on State The SIM980 stores its operation state input channel configuration in non volatile memory At power on the SIM980 will return to its previous configuration after a brief system check and initialization 1
21. ation cycle by disconnecting all inputs and outputs from the SIM980 and pressing and holding any of the con trol buttons for 5 seconds The entire process takes approximately 1 minute and is completed when the relays have stopped clicking for at least 10 seconds Note that it is important that all inputs be open or preferably shorted to ground before initiating an offset autocalibration cycle If any input channel is above 500 uV amplitude the SIM980 will reject the autocalibration request 1 2 1 4 Input Overload Each of the four input channels of the SIM980 has an overload de tection circuit The input is considered overloaded when the signal magnitude exceeds 10 V This is indicated by the red OVLD LED at the top of each front panel block SIM980 Analog Summing Amplifier SRS 1 4 Getting Started 1 2 2 Output 1 3 SIM Interface A CAUTION The resulting sum of the enabled input channels appears at the output BNC connectors on the front and rear panels Each output connection is through a 50 Q resistor For normal operation the user should not need to terminate the output If a 500 termination is applied note that the output signal will be divided in half If the output signal exceeds 10 V the output overload detection is activated This is indicated by the red OVLD near the top of the OUTPUT block on the front panel The primary connection to the SIM980 Summing Amplifier is the rear pane
22. c List of Commands aaa aa aaa 23 introduction de A ds 2 4 Commands 0000 eee eee ene 2 5 Status Model 0 000000 ae 3 Performance Tests 3 1 Introduction 265 R S RE rd Rod a 3 2 Tools and preparation 3 3 Precalibration Values 3 4 Calibration 0 00000 eee eee 3 5 Other tests and adjustments 3 6 SIM980 Performance Test Record 4 Circuitry 4 1 Circuit DESCANSE GAS wks Ad Parts Lists asis sn field K gcd See a a id 4 3 Schematic Diagrams ir a ii Contents ASRS SIM980 Analog Summing Amplifier General Information Service The SIM980 Summing Amplifier part of Stanford Research Sysetems Small Instrumentation Modules family is a four input unity gain amplifier for combining multiple analog signals from DC to 1 MHz Do not install substitute parts or perform any unauthorized modifi cations to this instrument The SIM980 is a single wide module designed to be used inside the SIM900 Mainframe Do not turn on the power until the module is completely inserted into the mainframe and locked in place iii iv General Information Symbols you may Find on SRS Products Alternating current Caution risk of electric shock Frame or chassis terminal Caution refer to accompanying documents Earth ground terminal fs RS SIM980 Analog Summing Amplifier General Information Notation A WARNING A CAUTIO
23. circuitry 4 2 4 1 2 Summing circuitry 4 2 4 1 3 a A 4 2 4 1 4 Offset measurement amp control 4 3 4 1 5 Digital control 4 3 4 2 Parts Lists oe tacto R RT ad aabt ds de 4 4 4 3 Schematic Diagrams 4 5 4 2 Circuitry 4 1 Circuit Descriptions 4 1 1 Input circuitry 4 1 2 Summing circuitry 4 1 3 Output circuitry Each channel of the SIM980 Summing Amplifier contains a JFET unity gain input buffer amplifer U201 U204 with input protection D201 D204 These input buffers have 0 1 uV C offset voltage drift and are being automatically trimmed to zero offset voltage by means ofan eight channel digital analog converter U403 Input buffer ampli fiers are powered by LDO voltage regulators U401 and U402 which are set to 13 0 V and 13 0 V respectively Discriminators U205 U208 provide under overvoltage detection for each channel and U209 monitors the output voltage The OVLDALL signal is generated by or ing overload signals into a single chan nel This signal restarts the module s microcontroller clock which is inactive in normal operation to minimize noise The clock is also automatically activated by a button push or a serial command The buffered input signals are summed into precision 0 1 resistor networks R200A E and R201A E which form a difference amplifier with gain 1 around the fast precision amplifier U210 The signal path is controlled by relays
24. cision power supply volt ages for the input buffer amplifiers These 13 0 V and 13 0 V volt ages can be tested at test points TP401 13 0 V TP402 13 0 V and TP403 ground R405 and R402 can be used to adjust the 13 0 V and 13 0 V voltage There should be no need to ever actually perform this factory adjustment If either voltage shows a large gt 100 mV deviation from its ideal value the module might have been damaged and should be sent to the factory for repair ASRS SIM980 Analog Summing Amplifier 3 6 SIM980 Performance Test Record 3 7 3 6 SIM980 Performance Test Record This page should be photocopied to record results General Name Serial Number Date Time Offset Voltage Output uV Channel 1 uV Channel 2 uV Channel 3 uV Channel 4 uV Calibration Words OFST 1 OFST 2 OFST 3 OFST 4 OFST 5 OFST 6 Gain DC mismatch AC mismatch 00 mV rms peak peak 1MHz 1V 00 mV rms peak peak TOSO mV O 0 mV 00 mV OO mV O O mV O O mV O FO mV O O mV LO mV OO mV SIM980 Analog Summing Amplifier ASRS Performance Tests ASRS SIM980 Analog Summing Amplifier 4 Parts Lists and Schematics This chapter presents a brief description of the SIM980 circuit design A complete parts list and circuit schematics are included In This Chapter 4 1 Circuit Descriptions 4 2 4 1 1 Input
25. etected error The error code can be queried with LCME User Request Indicates a front panel button was pressed Power On Indicates that an off to on transition has occurred 2 5 4 Standard Event Status Enable ESE The ESE acts as a bitwise AND with the ESR register to produce the single bit ESB message in the Status Byte Register SB It can be set and queried with the ESE command SIM980 Analog Summing Amplifier SRS Remote Operation This register is cleared at power on 2 5 5 Communication Error Status CESR The Communication Error Status register consists of 8 event flags each of which is set by the corresponding event and cleared only by reading or with the CLS command Reading a single bit with the CESR i query clears only bit i Weight Bit Flag 1 0 PARITY 2 1 FRAME 4 2 NOISE 8 3 HWOVRN 16 4 OVR 32 5 RTSH 64 6 CTSH 128 7 DCAS PARITY FRAME NOISE HWOVRN OVR RTSH CTSH DCAS Parity Error Set by serial parity mismatch on incoming data byte Framing Error Set when an incoming serial data byte is missing the STOP bit Noise Error Set when an incoming serial data byte does not present a steady logic level during each asynchronous bit period window Hardware Overrun Set when an incoming serial data byte is lost due to internal processor latency Causes the Input Buffer to be flushed and resets the command parser Input Buf
26. face directly to the DB 9 male DTE RS 232 port typically found on contemporary personal computers a cable must be made with a female DB 15 socket to mate with the SIM980 and a female DB 9 socket to mate with the PC s serial port Separate leads from the DB 15 need to go to the power supply making what is sometimes know as a hydra cable The pin connections are given in Table 1 2 The initial serial port settings at power on are 9600 Baud 8 bits no parity 1 stop bit and RTS CTS flow control The serial baud rate is fixed but the word size and parity may be changed with the FLOW or PARI commands 7 Although the serial interface lines on the DB 15 do not satisfy the minimum voltage levels of the RS 232 standard they are typically compatible with desktop SIM980 Analog Summing Amplifier personal computers SRS Getting Started DB 15 F to SIM980 Name DB 9 F 337 48 10 lt gt 3 11 2 5 RTS CTS TxD RxD Computer Ground to P S 7 gt 15VDC 13 14 89 1 5 VDC 15 VDC Ground P S return current Signal Ground separate wire to Ground Table 1 2 SIM980 Di rect Interface Cable Pin Assignments ASRS SIM980 Analog Summing Amplifier 2 Remote Operation In This Chapter This chapter describes operating the SIM980 over the serial interface 2 1 2 2 2 3 2 4 2 5 Index of Common Commands 2 2 Alphabetic List of Commands
27. fer Overrun Set when the Input Buffer is overrun by incoming data Causes the Input Buffer to be flushed and resets the command parser Undefined for the SIM980 Command Error Indicates a parser detected error Undefined for the SIM980 Device Clear Indicates the SIM980 received the Device Clear signal an RS 232 break Clears the Input Buffer and Output Queue and resets the command parser 2 5 6 Communication Error Status Enable CESE The CESE acts as a bitwise AND with the CESR register to produce the single bit CESB message in the Status Byte Register SB It can be set and queried with the CESE command ASRS SIM980 Analog Summing Amplifier 2 5 Status Model 2 21 This register is cleared at power on 2 5 7 Overload Status OVCR The Overload Condition Register consists of 5 single bit monitors of conditions within the SIM980 Bits in the OVCR reflect the real time values of their corresponding signals Reading the entire register or individual bits within it does not affect the OVCR Weight Bit Flag 1 0 Overload Channel 1 2 1 Overload Channel 2 4 2 Overload Channel 3 8 3 Overload Channel 4 16 4 Overload Output 32 5 undef 0 64 6 undef 0 128 7 undef 0 Overload Channel n The input buffer for Channel n is overloaded input voltage exceeds 10 V Note that the overload detection is active even if the channel is off Overload Output The output of the summing
28. ice request will only pulse the STATUS signal low for a minimum of 1 us The default behavior is to latch STATUS low until a STB query is received At power on PSTA is set to OFF PSTA OFF Interface Commands Interface commands provide generic control over the interface be tween the SIM980 and the host computer RST Example Reset Reset the SIM980 to default configuration After RST all channels are set to positive polarity and to off This is equivalent to the following command sequence CHAN 0 1 CHAN 0 0 RST SIM980 Analog Summing Amplifier SRS Remote Operation IDN Example Identify Read the device identification string The identification string is formatted as Stanford_Research_Systems SIM980 s n ver where is the 6 digit serial number and is the firmware revision level TDN Stanford_Research_Systems SIM980 s n003075 ver1 21 OPC Example Operation Complete Operation Complete Sets the OPC flag in the ESR register The query form OPC writes a 1 in the output queue when complete but does not affect the ESR register OPC CONS z Example Console Mode Set query the Console mode to Z OFF 0 ON 1 CONS causes each character received at the Input Buffer to be copied to the Output Queue At power on and Device Clear CONS is set to OFF CONS 0 LEXE Example Execution Error Query the las
29. ion 3 3 3 and record the results 3 4 3 AC Gain Calibration The SIM980 amplifier bandwidth rolls off around 6 MHz This is ac complished with a combination of fixed capacitors and one trimcap The trimcap can be adjusted to equalize high frequency gain below approximately 1 MHz maximizing the average common mode rejec tion between channels Just as in case of the DC gain the module achieves matching on the order of 60 dB Above 1 MHz high order effects begin to dominate and AC gains will vary from channel to channel by more than 50 dB However even the worst case channels typically achieve 40 dB 1 gain difference suppression for any frequency below their 3 dB bandwidth as long as all amplifiers operate in small signal mode i e the slew rate limit is not exceeded For sinusoidal signals this translates into 10 V amplitude at 500kHz and 1V at 5MHz Care must be taken with non sinusoidal signals which have high slew rate For this adjustment a 1 MHz sine wave generator and an AC volt meter or oscilloscope are necessary Connect the instruments as previously in section 3 3 4 Again it is crucial that all BNC cables are of exactly the same length and type and that the splitting of the signal is accomplished in a symmetric manner Differences in cable length will introduce phase SIM980 Analog Summing Amplifier SRS Performance Tests shifts between inputs and falsify the result If in doubt as a check of
30. ip ahead to section 3 4 Precalibration values should be recorded on a separate copy of the performance test record page 3 7 Begin by disconnecting all inputs from the SIM980 and connecting the output to the voltmeter Switch all channels to OFF and record the output voltage as Offset Voltage Output Enable Channel 1 set the polarity to and record the output voltage Change the polarity to and subtract this output voltage from the previous value Record the difference as Offset Voltage Channel 1 Disable Channel 1 and repeat for the remaining 3 channels ASRS SIM980 Analog Summing Amplifier 3 3 Precalibration Values 3 3 2 Calibration Words 3 3 3 DC Gain Match 3 3 4 AC Gain Match Next query the SIM980 over the remote interface to determine the calibration word values Send the remote queries OFST 1 OFST 6 and record the results Set the DC voltage source to 2V Connect the BNC Tee adapters together to form a 1 to 4 splitter Connect the splitter to the DC voltage source and connect the four SIM980 inputs to the splitter with equal length cables important for AC testing later Enable all four input channels and set all input polarities to Note the output voltage as V7 Then change all four input polarities to and note the output voltage as V_ Now switch the DC voltage source to 2 V and with the channel polarities still set to note the output voltage as V Change a
31. is set to 1 Upon querying an event register any set bits within it are cleared These are sometimes known as sticky bits since once set a bit can only be cleared by reading its value Event register names end with SR These read write registers define a bitwise mask for their cor responding event register If any bit position is set in an event register while the same bit position is also set in the enable register then the corresponding summary bit message is set Enable register names end with SE Communication Error Status DCAS Device Clear 7 CTSH CTS Halted 6 6 RTSH RTS Halted 5 5 OVR Input Buffer Overrun 4 4 3 3 2 2 1 T Standard Event TT HWOVRN Hardware Overrun NOISE Noise Error FRAME Framing Error PARITY Parity Error 0 0 CESR CESE PON Power On URQ User Request Status Byte DDE Device Error QYE Query Error el lt slwl ESR m a m Overload Status undef undef undef OVLD_OUTPUT OVLD_CH4 OVLD_CH3 OVLD_CH2 OVLD_CH1 of s xx OVCR OVSR OVSE Figure 2 1 Status Register Model for the SIM980 SIM980 Analog Summing Amplifier 4 SRS 2 18 Remote Operation 2 5 1 Status Byte SB The Status Byte is the top level summary of the SIM980 status model When masked by the Service Request Enable register a b
32. it set in the Status Byte causes the STATUS signal to be asserted on the rear panel SIM interface connector Typically STATUS remains asserted low until a STB query is received at which time STATUS is deasserted raised After clear ing the STATUS signal it will only be re asserted in response to a new status generating condition Weight Bit Flag 1 0 OVSB 2 1 undef 0 4 2 undef 0 8 3 undef 0 16 4 IDLE 32 5 ESB 64 6 MSS 128 7 CESB OVSB IDLE ESB MSS CESB Overload Status Summary Bit Indicates whether one or more of the enabled flags in the Overload Status Register has become true Indicates that the Input Buffer is empty and the command parser is idle Can be used to help synchronize SIM980 query responses Event Status Bit Indicates whether one or more of the enabled events in the Standard Event Status Register is true Master Summary Status Indicates whether one or more of the enabled status messages in the Status Byte register is true Note that while STATUS is released by the STB query MSS is only cleared when the underlying enabled bit message s are cleared Communication Error Summary Bit Indicates whether one or more of the enabled flags in the Communication Error Status Register has become true Bits in the Status Byte are not cleared by the STB query These bits are only cleared by reading the underlying event registers or by clearing
33. l DB 15 SIM interface connector Typically the SIM980 is mated to a SIM900 Mainframe via this connection either through one of the internal Mainframe slots or the remote cable interface It is also possible to operate the SIM980 directly without using the SIM900 Mainframe This section provides details on the interface The SIM980 has no internal protection against reverse polarity missing supply or overvoltage on the power supply pins Misapplication of power may cause circuit damage SRS recommends using the SIM980 together with the SIM900 Mainframe for most applications 1 3 1 SIM interface connector 1 3 2 Direct interfacing The DB 15 SIM interface connector carries all the power and commu nications lines to the instrument The connector signals are specified in Table 1 1 The SIM980 is intended for operation in the SIM900 Mainframe but users may wish to directly interface the module to their own systems without the use of additional hardware The mating connector needed is a standard DB 15 receptacle such as Amp part 747909 2 or equivalent Clean well regulated supply voltages of 15 5 VDC must be provided following the pin out specified in Table 1 1 Ground must be provided on pins 1 and 8 with chassis ground on pin 9 The STATUS signal may be monitored on pin 2 for a low going TTL compatible output indicating a status message ASRS SIM980 Analog Summing Amplifier 1 3 SIM Interface Direction Pin
34. ll four input polarities to and finally note the output voltage as Vi Calculate the gain ratio mismatch as Wr VT 1 x 100 en and record this value as the DC mismatch Using the same 1 to 4 splitter from section 3 3 3 connect all four input channels to the sine generator set to create a 1 MHz sine wave at 1 Vrms or 1 Vpeak peak amplitude circle which Unlike the DC case here it is important that all four BNC cables leading to the channel inputs are of exactly the same length and type and that the splitting of the signal is accomplished in a symmetric manner Differences in cable length will introduce phase shifts between inputs and falsify the result Connect the output of the SIM980 to the oscilloscope Separately trigger the scope synchronously with the sine generator AC matching is measured pairwise between channels with the two channels under test set to opposite polarity and the remaining two channels switched off There are 12 such permutations which can be labeled with a OO notation For example setting Channel 1 SIM980 Analog Summing Amplifier SRS Performance Tests 3 4 Calibration 3 4 1 Offset Adjustment non inverting Channel 3 inverting and Channels 2 amp 4 off is noted as FO 0O Measure the amplitude for each permutation and record the results circle either RMS or peak to peak Prior to beginning calibration photocopy a blank version of the per formance test
35. ods Four separate clock starting signals are combined by U106 e Power on reset e Amplifier overload any e Incoming serial data e Front panel button press The fast start time of the RC oscillator ensures that incoming se rial data will be correctly decoded by the microcontroller s UART even when the clock is started by the serial start bit of the incoming data When the microcontroller has completed all pending activity it drives the STOP signal high pin 71 of U101 effectively halting its own processor clock In this way the SIM980 guarantees no digital clock artifacts can be generated during quiescent operation SIM980 Analog Summing Amplifier SRS 4 4 Circuitry 4 2 Parts Lists Part Reference SRS P N Value Part Reference SRS P N Value C101 C102 C103 5 00098 10u T R116 R124 R125 4 01465 270 C104 5 00381 330p R117 R126 R127 R223 4 01455 100 C105 5 00106 9 0 50p R226 R229 R232 R238 C106 C107 C108 C405 5 00387 1000p R284 R287 R292 C201 C203 5 00319 10U T35 R128 R246 R265 R288 4 01406 0 C202 5 00368 27P R202 R204 R206 R208 4 01405 1 00M C204 C215 5 00318 2 2U T35 R209 R211 4 01259 30 1K C217 5 00104 3 5 20P R210 R212 4 01309 100K C218 5 00363 10P R222 R225 R228 R231 4 01535 220K C220 5 00313 1P R267 C222 C223 5 00454 01U R233 R239 4 01419 3 3 C401 C404 X101 106 5 00299 1U R234 R237 4 01675 100 5 1 2W X108 X114 X201 X224 R245 4 00617 100K D101 D102 D402 3 00945 BAT54S R249 R252 R255 R259 4 01487
36. ount from the automatic result Otherwise the module should be power cycled and the adjustment procedure should be repeated Record the final offset values and final calibration words on the performance test record ASRS SIM980 Analog Summing Amplifier 3 4 Calibration 3 5 3 4 2 DC Gain Calibration All resistors of the SIM980 gain network have a precision of 0 1 Any two channels can therefore differ in their gain by up to 0 2 Gain between and polarity settings can also differ by 0 2 The common mode rejection of two channels set to take the difference of two signals is therefore limited to 0 2 or approximately 54 dB worst case The module has one trimpot to equalize the average positive gain over all channels with the average negative gain and give the best overall match for any combination of channels To find the optimum setting repeat the setup of section 3 3 3 Set the DC voltage source to approximately 2 V output and set all four input channels to polarity Note the DC output voltage with at least millivolt precision the value should be 8 00 V Now switch all four channels to and adjust trimpot R268 to bring the output voltage to the same magnitude but opposite polarity as previously noted Be aware that this procedure depends on neglecting the input offset voltages so be sure to perform section 3 4 1 first After completing the calibration measure the DC gain match accord ing to sect
37. rease by about 4 4 uV per count while increasing j for 6 causes the output voltage to increase with roughly the same sensitivity All 6 offset values can be simultaneously set to a single value j by OFST 0 j Note however there is no corresponding multi channel ASRS SIM980 Analog Summing Amplifier 2 4 Commands Example query Values stored by OFST or ACAL are stored in non volatile memory and are not affected by power cycling or RST OFST 4 106 2 4 6 Serial Communication Commands FLOW z Example Flow Control Set query flow control to Z NONE RTS 1 XON 2 After power on modules default to FLOW RTS flow control FLOW 0 PARI z 2 4 7 Status Commands Example Parity Set query parity to z NONE ODD 1 EVEN 2 MARK 3 SPACE 4 After power on modules default to PARI NONE PARI EVEN The Status commands query and configure registers associated with status reporting of the SIM980 STB 1 Example Status Byte Reads the Status Byte register bit Execution of the STB query without the optinal bit always causes the STATUS signal to be deasserted Note that STB i will not clear STATUS even if bit i is the only bit presently causing the STATUS signal See also the PSTA command STB 16 SRE i i Example Service Request Enable Set query the Service Request Enable register bit i to j SRE 0 1
38. record page 3 7 Calibration starts by disconnecting all inputs and resetting the elec tronic output offset calibration constants This is accomplished by issuing the remote commands CHAN 0 0 OFST 5 128 OFST 6 127 which set the electronic trim DAC outputs to midpoint Connect the SIM980 output to the voltmeter and adjust R245 to zero the voltage reading After nulling R245 an unconditional autocalibration cycle should be initiated Issue the following remote commands ARMC FORCE ACAL to arm and start internal calibration The autocalibration will com plete in approximately one minute wait for relays to cease switching for at least 10 seconds The output voltage will fluctuate during cal ibration but settle to less than 20 uV Verify that the calibration words are within the valid range 1 254 by repeating the queries of section 3 3 2 Nominally all calibration words should be within the range 50 200 values of 0 or 255 indicate that the offsets have shifted outside of the adjustable range and the SIM980 may be damaged Input offset voltages should be measured directly by the procedure of section 3 3 1 Except for short term drift the calibration should reduce input offset voltage errors to less than 10 pV If the result is un satisfactory adjustment of the calibration constant may be attempted by manually issuing explicit OFST commands see section 2 4 5 Manually adjusted constants should differ only slightly 1 c
39. return the text keyword otherwise they return the decimal integer value Thus the only possible responses to the TOKN query are ON and 9 On reset TOKN is set to OFF Example TOKN OFF SIM980 Analog Summing Amplifier SRS Remote Operation Example Response Termination Set query the term sequence to Z NONE 0 CR 1 LF 2 CRLF 3 LFCR 4 The term sequence is appended to all query responses sent by the module and is constructed of ASCII character s 13 car riage return and 10 line feed The token mnemonic gives the sequence of characters At power on TERM is set to CRLF TERM 3 ASRS SIM980 Analog Summing Amplifier 2 5 Status Model 2 5 Status Model The SIM980 status registers follow the hierarchical IEEE 488 2 for mat A block diagram of the status register array is given in Figure 2 1 There are three categories of registers in the SIM980 status model Condition Registers Event Registers Enable Registers 7 6 CME Command Error 5 EXE Execution Error 4 3 2 1 0 INP Input Buffer Error OPC Operation Complete These read only registers correspond to the real time condi tion of some underlying physical property being monitored Queries return the latest value of the property and have no other effect Condition register names end with CR These read only registers record the occurrence of defined events When the event occurs the corresponding bit
40. s may take either set or query form depending on whether the character follows the mnemonic Set only commands are listed without the query only commands show the after the mnemonic and optionally query commands are marked with a Parameters shown in and are not always required Parameters in are required to set a value and are omitted for queries Parameters in are optional in both set and query commands Parameters listed without any surrounding characters are always required Do not send or or as part of the command Multiple parameters are separated by commas Multiple commands may be sent on one command line by separating them with semi colons so long as the input buffer does not overflow Commands are terminated by either CR or LF characters Null commands and whitespace are ignored Execution of command s does not begin until the command terminator is received Token parameters generically shown as Z in the command de scriptions can be specified either as a keyword or integer value Command descriptions list the valid keyword options with each keyword followed by its corresponding integer value For example to set the response termination sequence to CR lt LF the following two commands are equivalent TERM CRLF or TERM 3 For queries that return token values the return format keyword or integer is specified with the TOKN command SIM980
41. t execution error code A query of LEXE always clears the error code so a subsequent LEXE will return 0 Valid codes are Value Definition 0 No execution error since last LEXE 1 Illegal value 2 Wrong token 3 Invalid bit 16 Autocalibration not armed STB 12 LEXE LEXE 3 0 The error 3 Invalid bit is because STB only allows bit specific queries of 0 7 The second read of LEXE returns 0 ASRS SIM980 Analog Summing Amplifier 2 4 Commands 2 15 LCME Command Error Query the last command error code A query of LCME always clears the error code so a subsequent LCME will return 0 Valid codes are Value Definition No execution error since last LCME Illegal command Undefined command Illegal query Illegal set Missing parameter s Extra parameter s Null parameter s Parameter buffer overflow Bad floating point 10 Bad integer 11 Bad integer token 12 Bad token value 13 Bad hex block 14 Unknown token GO 4 G dF WNF O NO Example IDN LCME 4 The error 4 Illegal set is due to the missing LBTN Button Query the channel number of the last button pressed A query of LBTN always clears the button code so a subsequent LBTN will return 0 Example LBTN 1 TOKN z Token Mode Set query the Token Query mode to Z OFF 0 ON 1 If TOKN ON is set then queries to the SIM module that return to kens will
42. ult in harmful voltages being present on the BNC shell The opamp buffer combination U210 U211 does not by itself satisfy the offset voltage specifications of the SIM980 Offset voltage stabil ity is therefore guaranteed by U212 a differential integrator which drives a differential current source QN201A B to trim the input offset voltage of U210 The resulting amplifier combines the AC per formance of U210 with the stability of the slow amplifier U212 Offset adjustment is performed by two outputs of digital analog converter U403 4 1 4 Offset measurement amp control 4 1 5 Digital control Chopper stabilized amplifier U404 is set at a gain of 1000 to mea sure output offset voltages with the 10 bit built in analog digital converter of microcontroller U101 In auto calibration mode the mi crocontroller can resolve microvolt output voltages and set channels 1 6 of digital analog converter U403 to minimize any input and the output offset voltage Chopper amplifier U404 is switched off dur ing normal operation to eliminate the potential noise generated by its internal chopping circuit The SIM980 is controlled by microcontroller U101 A critical aspect of the design is the clock stop circuitry implemented by U103 and U105 A simple RC oscillator is enabled or disabled at pin 1 of U105 which is driven by synchronizing flip flop U103B to ensure that no runt clock pulses are produced that would violate U101 s minimum clock peri
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