MODEL COM-2S USER MANUAL
Contents
1. Installing COM Ports in Windows Operating Systems NOTE COM boards can be installed in virtually any operating system and we do support installation in earlier versions of Windows and are very likely to support future version as well For use in WinCE contact the factory for specific instructions Windows NT4 0 To install the COM ports in Windows NT4 you ll need to change one entry in the registry This entry enables IRQ sharing on multi port COM boards The key is HKEY_LOCAL_MACHINE SYSTEM CurrentControlSet Services Serial The name of the value is PermitShare and the data should be set to 1 You ll then add the board s ports as COM ports setting the base addresses and IRQs to match your board s settings To change the registry value run RegEdit from the START RUN menu option by typing REGEDIT ENTER in the space provided Navigate down the tree view on the left to find the key and double click on the name of the value to open a dialog allowing you to set the new data value Advanced Settings for New Port x COM Port Number eae y Base 1 0 Port Address 03F8 y Cancel Interrupt Request Line IRQ Help M FIFO Enabled 15 y To add a COM port use STARTICONTROL PANEL PORTS applet and click ADD then enter the correct UART address and Interrupt number When the Add New Port dialog is configured click OK but answer Don t Restart Now when prompted until you ve added any other ports as well Th2. 0 to switches in the ON position For example as illustrated in the following table switch selection corresponds to binary 10 1101 1xxx hex 2D8 The xxx represents address lines A2 A1 and AO used on the card to select individual registers See Chapter 5 Programming Switch Label Binary Represent n Conversion HEX Represent n Table 4 3 Example Address Setup 20 Manual COM 2S Review the Address Selection Table carefully before selecting the card address If the addresses of two circuits overlap you will experience unpredictable computer behavior The following table lists standard DOS COM Port addresses Address Switch Settings Serial IRQ Base Hex COM Port Address A9 A8 A7 A6 A5 A4 A3 COM1 IRQ 4 COM3 IRQ 4 Table 4 4 Standard DOS COM Port Addresses Notice that only two interrupts are assigned to four serial ports 21 Manual COM 2S Chapter 5 Programming Sample Programs There are sample programs provided with the COM 2S card in C Pascal QuickBASIC and several Windows languages DOS samples are located in the DOS directory and Windows samples are located in the WIN32 directory Windows Programming The COM 2S card installs into Windows as COM ports Thus the Windows standard API functions can be used In particular CreateFile and CloseHandle for opening and closing a port gt SetupComm SetCommTimeouts GetCommState and SetCommState to set and change a port s
3. for purposes of this warranty is defined as any use to which the equipment is exposed other than that use specified or intended as evidenced by purchase or sales representation Other than the above no other warranty expressed orimplied shall apply to any and all such equipment furnished or sold by ACCES 3 Manual COM 2S Table of Contents Chapter t Introduction sieaa 6645 4 bd dub ii wee ee dw Pe Hed eR a Be be 5 Multi Protocol Operatlon_ lt e ee 5 RS485 and RS422 Balanced Mode Operation ea eee 5 COM Port Compatibility cia ve alan aa a Wee AER od aa see eee leas kate ale kG Read 5 Communication Modes gt sica al ake le SOG E AL aap alee a ane BP leaks ed ADOS a ale aden 5 RTS and Auto RTS Transceiver Control cc eee 6 CE Marking et Bests losas Antaris A a aes A Bae St ee eke eke A Cae ia o 6 Specifications aa KN a A Gaga te oe ee Gee ee Dee Eo ed oe eee 7 Figure 1 1 COM 2S Block Diagram 0000 eee 8 Chapter 2 Installation 2 2 0 02 0002 NG nah A ee eee r ee a ee ee eee ee 9 Installing COM Ports in Windows Operating Systems a ee 11 W indows NFA O rrer a vane a es i deb Mew een wg A ade ee ane oe 11 Windows XP an 24 A eee A eee ee Re bea aot bed Bat eee ek te PE eee Seed 11 Chapter 3 Option Selection o Gecesi si esati a Ga a a a a a aa eee 15 Figure 3 1 Simplified Termination Schematic aaa eee 15 Figure 3 2 COM 2S Option Selection Map aa e
4. Street San Diego CA 92121 Tel 858 550 9559 FAX 858 550 7322 www accesio com 31 Manual COM 2S
5. altering states of other bits while data i While there is data to send while inportb BASEADDR 5 amp 0x20 Wait until transmitter is empty outportb BASEADDR data i Athy outportb BASEADDR 4 inportb BASEADDR 4 amp 0xFD Reset RTS bit without altering states of other bits Caution The OUT2 bit of the UART must be set low for proper interrupt driven communication This bit enables or disables the interrupts and the card will not communicate if the bit is pulled high 26 Manual COM 2S Chapter 6 Connector Pin Assignments The popular 9 pin D subminiature connector is used for interfacing to communication lines The connector is equipped with 4 40 threaded standoffs female screw lock to provide strain relief Pin No RS232 Functions RS422 485 Functions DCD Data Carrier Detect Input Rx Receive Data 2 RD Receive Data input Tx Transmit Data 3 TD Transmit Data output Tx Transmit Data 4 DTR Data Terminal Ready output 5 Gnd Signal Ground GND Ground 6 DSR Data Set Ready input 7 RTS Request to Send output 8 CTS Clear to Send input 9 RI Ring Indicator input Table 6 1 Connector Pin Assignments Note For Simplex Half Duplex and Full Duplex operation see Chapter 3 Option Selection in this manual for pin connection information Note If connections are to be made to a COM 2S CE marked version then CE certifiable cabling
6. be redundant and may skip forward to begin developing your application The software provided with this ISA Board is on CD and must be installed onto your hard disk prior to use To do this perform the following steps as appropriate for your operating system CD Installation The following instructions assume the CD ROM drive is drive D Please substitute the appropriate drive letter for your system as necessary DOS 1 Place the CD into your CD ROM drive 2 Type OLJed to change the active drive to the CD ROM drive 3 Type UNHA to run the install program 4 Follow the on screen prompts to install the software for this board WINDOWS 1 Place the CD into your CD ROM drive 2 The system should automatically run the install program If the install program does not run promptly click START RUN and type QJ OI is click OK or press eed 3 Follow the on screen prompts to install the software for this board LINUX 1 Please refer to linux htm on the CD ROM for information on installing serial ports under linux Installing the Hardware Before installing the board carefully read Chapter 3 and Chapter 4 of this manual and configure the board according to your requirements The SETUP Program can be used to assist in configuring jumpers on the board Be especially careful with Address Selection If the addresses of two installed functions overlap you will experience unpredictable computer behavior To help avoid this problem r
7. the board and Click OK Close the Set Configuration Manually dialog and Click Finish Click Do Not Reboot if you wish to install more ports Repeat all of the above steps entering the same IRQ but using the configured Base address for each additional UART When you are done installing ports reboot the system normally 14 Manual COM 2S Chapter 3 Option Selection To help you locate the jumpers described in this section refer to the Option Selection Map at the end of this chapter Operation of the serial communications section is determined by jumper installation as described in the following paragraphs 232 422 Jumpers must be installed in these blocks for each COM port The function of the 232 and 422 jumpers are to configure the port for single ended RS232 communications or differential RS422 485 mode communications Echo This jumper enables local echoing of transmitted characters back to the receiver Itis used to confirm locally that a character was transmitted and may be installed for two wire half duplex RS485 mode Auto or RTS Only one jumper may be installed for each COM port These jumpers select either the Automatic or RTS line control modes for RS485 operation To operate with Windows programs select Automatic Terminations and Bias A transmission line should be terminated at the receiving end in its characteristic impedance Installing a jumper at the location labeled TERM applies a 120Q l
8. to the baud rate of the data Note For use with Windows programs COM 2S must be operated in the Auto RTS mode Under RTS control your software must set the RTS bit to a logic 1 to enable the driver and logic 0 to disable the driver The receiver is also normally disabled during RS485 transmissions See Chapter 3 Option Selection for details on setting the Auto and RTS modes and for enabling or disabling local echoing of characters In normal RS485 communication the echo is turned off to prevent data being echoed back CE Marking If your card is CE marked it meets the requirements of EN50081 1 1992 Emissions EN50082 1 1992 Immunity and EN60950 1992 Safety 6 Manual COM 2S Specifications Communications Interface 1 0 Connection 9 pin male D sub connectors Serial Ports Two shielded male D sub 9 pin IBM AT style connectors compatible with RS 232 RS 422 and RS 485 specifications Character length 5 6 7 or 8 bits Parity Even odd or none Stop Interval 1 1 5 or 2 bits Serial Data Rates 50 to 115 200 Faster or custom rates available Asynchronous Type 16550 buffered UART e Address Continuously mappable within 000 to 3F8 hex range of AT I O bus addresses Caution The OUT2 bit of the UART must be set low for proper interrupt driven communication This bit enables or disables the interrupts and the card will not communicate if the bit is pulled high RS232 Drivers Device 75C18
9. 0 When done the UART is ready to use 24 Manual COM 2S Reception Reception can be handled in two ways polling and interrupt driven When polling reception is accomplished by constantly reading the Line Status Register at Base Address 5 Bit 0 of this register is set high whenever data are ready to be read from the chip A simple polling loop must continuously check this bit and read in data as itbecomes available The following code fragment implements a polling loop and uses a value of 13 ASCII Carriage Return as an end of transmission marker do while inportb BASEADDR 5 amp 1 Wait until data ready data i inportb BASEADDR while data i 13 Reads the line until null character rec d Interrupt driven communications should be used whenever possible and is required for high data rates Writing an interrupt driven receiver is not much more complex than writing a polled receiver but care should be taken when installing or removing your interrupt handler to avoid writing the wrong interrupt disabling the wrong interrupt or turning interrupts off for too long a period The handler would first read the Interrupt Identification Register at Base Address 2 If the interrupt is for Received Data Available the handler then reads the data If no interruptis pending control exits the routine A sample handler written in C is as follows readback inportb BASEADDR 2 if readback amp 4 Readb
10. 5 Quad Line Transceivers Output Voltage 6VDC minimum current limited to 10 mA Receiver threshold 1 5V high 0 75 low Maximum input 30VDC RS422 RS485 Differential Communication Mode e Multipoint Compatible with RS422 and RS485 specifications Up to 32 drivers and receivers allowed on line Serial communications ACE used is type NS16550 Driver Receivers used are type 75ALS180 e Receiver Input Sensitivity 200 mV differential input Common Mode Rejection 12V to 7V Transmitter Output Drive Capability 60 mA with thermal shutdown Environmental Operating Temperature Range 0 C to 60 C e Storage Temperature Range 50 C to 120 C e Humidity 5 to 95 non condensing Power Required 5VDC at 125 mA typical 12VDC at 5 mA typical 12VDC at 5 mA typical 750 mW total power consumption Size 6 1 2 long 3 4 length by 3 7 8 Although designed for a half length slot if the card is installed in an 8 bit XT style slot the card will work but higher order IRQs 10 15 will be unavailable 7 Manual COM 2S ADDRESS ae CRYSTAL LOGIC OSCILLATOR BAUD RATE GENERATOR COMPUTER ISA BUS IRQ SIGNAL AUTO RTS CIRCUITRY Figure 1 1 COM 2S Block Diagram Only one serial channel shown 8 Manual COM 2S Chapter 2 Installation A printed Quick Start Guide QSG is packed with the board for your convenience If you ve already performed the steps from the QSG you may find this chapter to
11. A ag 29 Figure A 1 Typical RS485 Two Wire Multidrop Network eee eee 30 4 Manual COM 2S Chapter 1 Introduction The COM 2S Serial Interface Card was designed for effective multipoint transmission The COM 2S is 6 5 inches long and may be installed in 8 or 16 bit slots of IBM PC XT AT or compatible computers If installed in an eight bit slot the high interrupts IRQ 10 15 will not be available to the COM 2S Multi Protocol Operation The COM 2S is a multi protocol serial card supporting RS232 RS422 or RS485 communications RS232 is the most common form of serial communication but is an unbalanced single line system unsuitable for distances over 50 feet RS422 is an extension of RS232 but uses differential or balanced line drivers to improve noise immunity and increase the maximum distance to 4000 feet RS485 improves on RS422 with switchable transceivers and the ability to support multiple devices on a single party line The RS485 specification defines a maximum of 32 devices on a single line The number of devices served on a single line can be expanded by use of repeaters RS485 and RS422 Balanced Mode Operation In addition to RS232 mode the COM 2S also supports RS422 and RS485 modes which use differential balanced drivers for increased range and noise immunity COM 2S also has capability to add bias voltages and to add load resistors to terminate the communications lines RS485 communications requires thatone transmit
12. V differential signal superimposed on common mode noise of 12 V or 7 V In case of communication conflict the driver receivers feature thermal shutdown Two sets of LED indicators are provided on the COM 2S card The LEDs blink to indicate activity on the transmitting and receiving lines and are useful for problem diagnosis Communication Modes COM 2S supports Simplex Half Duplex and Full Duplex communications in a variety of 2 and 4 wire cable connections Simplex is the simplest form of communications with transmission occurring only in one direction Half Duplex allows traffic to travel in both directions but only one way at a time In Full Duplex operation data travels in both directions at the same time RS485 communications commonly use the 5 Manual COM 2S half duplex mode since they share only a single pair of wires COM 2S also supports the option of locally echoing the characters back to the transmitter RTS and Auto RTS Transceiver Control In RS485 communications the driver must be enabled and disabled as needed allowing all cards to share a two wire or four wire cable The COM 2S card has two methods of controlling the driver automatic Auto and request to send RTS control With automatic control the driver is enabled when data is ready to be transmitted The driver remains enabled for the transmission time of one character after data transfer is complete and then is disabled The COM 2S automatically adjusts it s timing
13. ack will be set to 4 if data are available data i inportb BASEADDR outportb 0x20 0x20 Write EOI to 8259 Interrupt Controller return 25 Manual COM 2S Transmission RS485 transmission is simple to implement The AUTO feature of the COM 2S card automatically enables the transmitter when data are ready to send so no software enabling is required The following software example is for non AUTO operation First the RTS line should be set high by writing a1 to Bit 1 of the Modem Control Register at Base Address 4 The RTS line is used to toggle the transceiver from receive mode to transmit mode and vice versa It is not carried out on the line in RS485 and is not used for handshaking Similarly the CTS line is not used in RS485 and should always be enabled by installing a jumper as described earlier After the above is done the card is ready to send data To transmita string of data the transmitter must first check Bit 5 of the Line Status Register at Base Address 5 That bitis the transmitter holding re gister em pty flag Ifitis high the transmitter has sent the data The process of checking the bit until it goes high followed by a write is repeated until no data remains After all data has been transmitted the RTS bit should be reset by writing a 0 to Bit 1 of the Modem Control Register The following C code fragment demonstrates this process outportb BASEADDR 4 inportb BASEADDR 4 0x02 Set RTS bit without
14. al system the voltage produced by the driver appears across a pair of wires A balanced line driver will produce a differential voltage from 2 to 6 volts across its output terminals A balanced line driver can also have an input enable signal that connects the driver to its output terminals Ifthe enable signalis OFF the driver is disconnected from the transmission line This disconnected or disabled condition is usually referred to as the tristate condition and represents a high impedance RS485 drivers must have this control capability RS422 drivers may have this control butitis not always required A balanced differential line receiver senses the voltage state of the transmission line across the two signal input lines If the differential input voltage is greater than 200 mV the receiver will provide a specific logic state on its output If the differential voltage input is less than 200 mV the receiver will provide the opposite logic state on its output The maximum operating voltage range is from 6V to 6V allowing for voltage attenuation that can occur on long transmission cables 28 Manual COM 2S A maximum common mode voltage rating of 7V provides good noise immunity from voltages induced on the twisted pair lines The signal ground line connection is necessary in order to keep the common mode voltage within that range The circuit may operate without the ground connection but may not be reliable Parameter Condition Driver O
15. and breakout methodology Cable shields connected to ground at the mounting bracket shielded twisted pair wiring etc must be used 27 Manual COM 2S Appendix A Application Considerations Introduction Working with RS422 and RS485 devices is not much different from working with standard RS232 serial devices and these two standards overcome deficiencies in the RS232 standard First the cable length between two RS232 devices must be short less than 50 feet Second many RS232 errors are the result of noise induced on the cables The RS422 standard permits cable lengths up to 5000 feet and because it operates in differential mode it is more immune to induced noise Connections between two RS422 devices with CTS ignored should be as follows Device 1 Device 2 Signal COM 2S 25 pin Signal COM 2S 25 pin 9 pin 9 pin Table A 1 Connections Between Two RS422 Devices A third deficiency of RS232 is that more than two devices cannot share the same cable This is also true for RS422 but RS485 offers all the benefits of RS422 plus allows up to 32 devices to share the same twisted pairs An exception to the foregoing is that multiple RS422 devices can share a single cable if only one will talk and the others will always receive Balanced Differential Signals The reason that RS422 and RS485 devices can drive longer lines with more noise immunity than RS232 devices is that a balanced differential drive method is used In a balanced differenti
16. ations Port The software for this device is now installed but may not work correctly Windows cannot determine the settings for this device Consult the documentation that came with this device and use the Resource tab to set the configuration Code 34 To close this wizard click Finish Bec E Click the View or change resources for this hardware Advanced link 12 Select Add a new hardware device from the bottom of the list presented and Click Next Manual COM 2S MidHardware reed Properties Resources Resource settings F Communications Port COM13 i This device isn t using any resources because it has a problem Set Configuration Manually Click the Set Configuration Manually button Select Basic Configuration 8 from the Settings Based on drop down list Select I O Range in the Resource Settings box and Click the Change Settings button Enter the base address of the board and Click OK Resources Resource settings Add hardware Wizard Properties Communications Port C0M13 Resource type 1 0 Range Setting 0300 0307 e Setting based on Basic configuration 0008 Use automatic settings Conflicting device list No conflicts 13 Select IRQ in the Resource Settings box and Click the Change Settings button Manual COM 2S Enter the IRQ of
17. avoid this conflict HEX RANGE 000 00F 020 021 040 043 060 06F 070 07F 080 09F 0A0 0BF 0C0 ODF OFO OF 1 0F8 0FF 170 177 1F0 1F8 200 207 238 23B 23C 23F 278 27F 2B0 2BF 2C0 2CF 2D0 2DF 2E0 2E7 2E8 2EF 2F8 2FF 300 30F 310 31F 320 32F 370 377 378 37F 380 38F 3A0 3AF 3B0 3BB 3BC 3BF 3C0 3CF 3D0 3DF 3E8 3EF 3F0 3F7 3F8 3FF USAGE 8237 DMA Controller 1 8259 Interrupt 8253 Timer 8042 Keyboard Controller CMOS RAM NMI Mask Reg RT Clock DMA Page Register 8259 Slave Interrupt Controller 8237 DMA Controller 2 Math Coprocessor Math Coprocessor Fixed Disk Controller 2 Fixed Disk Controller 1 Game Port Bus Mouse Alt Bus Mouse Parallel Printer EGA EGA EGA GPIB AT Serial Port Serial Port Hard Disk XT Floppy Controller 2 Parallel Printer SDLC SDLC MDA Parallel Printer VGA EGA CGA Serial Port Floppy Controller 1 Serial Port Table 4 1 Standard Address Assignments for Computers 19 Manual COM 2S I O bus address switches are marked A3 A9 The following table lists the switch labels vs the address line controlled and the relative weights of each Address Switch Settings 1st Digit 2nd Digit 3rd Digit Switch Label 7 6 5 4 3 2 1 Address Line Controlled A4 A3 Decimal Weight 512 128 Hexadecimal Weight 100 10 a Ee ee Table 4 2 COM 2S Address Switches In order to read the address switch setup assign a binary 1 to switches that are turned OFF and a binary
18. e 18 Chapter 4 Address Selection eee 19 Table 4 1 Standard Address Assignments for Computers 0000002 c ee eeee 19 Table 4 2 COM 2S Address Switches 00000 eee 20 Table 4 3 Example Address Setup ga CS aM elt aha ok Sten tuts e etica di 20 Table 4 4 Standard DOS COM Port Addresses es ahh anki aaah ti i teil tice ht hae aaah a ot tla ae ee OR Ae AE fo La 21 Chapter 5 Programming assis asarana ana ung Bs ek a ees ae NE Ja ee BAS hin ates Bee a 22 Sample Program Si rris sien a ace dea REE Sle NENENG ME ee A aoe ay ae EN BR 22 Windows Programming aesan fete a ha AA A aa aa ka ee siete RoE pe Medd Ga et de AG ade we 22 Initialization ts sehen tie baa eee ete ee tetra dt fia ss Sle tE a el 22 Table 5 1 Baud Rate Divisor Values_ aaa aaa ee 23 RECeDtON see eke eet Rie deeded bg ae Metin wat Baw tai rae aed Pad ev teat Ride steed dala 25 Transmission sat ici a a adh hb ia ae ben de dt asa enya eh 26 Chapter 6 Connector Pin Assignments a eee 27 Table 6 1 Connector Pin Assignments A A tead nd Maia ann sa a petites Oca gait oh Malan dh 27 Appendix A Application Considerations ee eee eee 28 Introduction viii A ret Aaa toda ah Sige Pegs Heme Pitty harriers 28 Table A 1 Connections Between Two RS422 Devices 200000 eee eee 28 Balanced Differential Signals 0 0 02 0c eee 28 Table A 2 RS422 Specification Summary o td le KAN 29 RS485Data Transmission A a a B
19. e failure We will assign a Return Material Authorization RMA number which must appear on the outer label of the return package All units components should be properly packed for handling and returned with freight prepaid to the ACCES designated Service Center and will be returned to the customer s user s site freight prepaid and invoiced Coverage First Three Years Returned unit part will be repaired and or replaced at ACCES option with no charge for labor or parts not excluded by warranty Warranty commences with equipment shipment Following Years Throughout your equipments lifetime ACCES stands ready to provide on site or in plant service at reasonable rates similar to those of other manufacturers in the industry Equipment Not Manufactured by ACCES Equipment provided but not manufactured by ACCES is warranted and willbe repaired according to the terms and conditions of the respective equipment manufacturer s warranty General Under this Warranty liability of ACCES is limited to replacing repairing or issuing credit at ACCES discretion for any products which are proved to be defective during the warranty period In no case is ACCES liable for consequential or special damage arriving from use or misuse of our product The customer is responsible for all charges caused by modifications or additions to ACCES equipmentnot approved in writing by ACCES or ifin ACCES opinion the equipment has been subjected to abnormal use Abnormal use
20. efer to the FINDBASE EXE program installed from the CD The setup program does not set the options on the board these must be set by jumpers 9 Manual COM 2S To Install the Board f 2 3 4 N SINO Turn off computer power Remove the computer cover Remove the blank I O backplate Install jumpers for selected options from either the Option Selection section of this manual or the suggestions of our setup software program Select the base address on the card using either the Address Selection section of this manual or the suggestions for COM 2S in our FINDBASE setup software program Install the card in an I O expansion slot Install the I O cable Inspect for proper fit of the board and cable and tighten screws Turn the computer ON and observe the LED indicators The LED s will blink when there is any activity on the communication lines 10 Turn the computer OFF and replace the computer cover Note If installed in an eight bit slot IRQs 10 15 will be unavailable Two DB9 connectors are provided on the mounting bracket for input output connections To ensure that there is minimum susceptibility to EMI and minimum radiation it is important that the card mounting bracket be properly screwed into place and that there be a positive chassis ground Also proper EMI cabling techniques cable connect to chassis ground atthe aperture shielded twisted pair wiring etc be used for the input output wiring 10 Manual COM 2S
21. en restart the system normally or by selecting Restart Now Windows XP To install the COM ports in Windows XP you will be manually installing standard communications ports then changing the settings for resources used by the ports to match the hardware Run the Add Hardware applet from the Control Panel Click Next atthe Welcome to the Add New Hardware Wizard dialog You ll briefly see a searching message then Select Yes have already connected the hardware and Click Next 11 Manual COM 2S Add Hardware Wizard The following hardware is already installed on your computer Si Sy From the list below select an installed hardware device then click Next to check properties or troubleshoot a problem you might be having To add hardware not shown in the list click Add a new hardware device Installed hardware 4 ECP Printer Port LPT1 F Communications Port COM1 I Communications Port COM2 via Rev 5 or later USB Universal Host Controller USB Root Hub Add a new hardware device Select Install the hardware that manually select from a list and Click Next Select Ports COM amp LPT and Click Next Select Standard Port Types and Communications Port the defaults Click Next Click Next Addi hardware Wizard Completing the Add Hardware Wizard The following hardware was installed Communic
22. ended and is 12V to 7V Since any driver can be disconnected or tristated from the line it must withstand this common mode voltage range while in the tristate condition RS485 Two Wire Multidrop Network The following illustration shows a typical multidrop or party line network Note that the transmission line is terminated on both ends of the line but not at drop points in the middle of the line 29 Manual COM 2S TERMINATION RESISTORS AT BOTH ENDS ONLY ji TX ENABLE TX ENABLE RX ENABLE RX ENABLE TX ENABLE RX ENABLE Figure A 1 Typical RS485 Two Wire Multidrop Network RS485 Four Wire Multidrop Network An RS485 network can also be connected in a four wire mode In a four wire network it s necessary that one node be a master node and all others be slaves The network is connected so that the master communicates to all slaves and all slaves communicate only with the master This has advantages in equipment that uses mixed protocol communications Since the slave nodes never listen to another slave s response to the master a slave node cannot reply incorrectly 30 Manual COM 2S Customer Comments If you experience any problems with this manual or just want to give us some feedback please email us at manuals accesio com Please detail any errors you find and include your mailing address so that we can send you any manual updates MmACCES I O PRODUCTS INC 10623 Roselle
23. g a jumper in one of these locations If the COM 2S is installed in a short eight bit slot the higher interrupts IRQ10 through IRQ15 will be unavailable to the card 17 Manual COM 2S COM B DPPP WONDMARW COMA DPPSPDD OONMDURW Figure 3 2 COM 2S Option Selection Map Switches S1 COM B Address Illustration above shows switches set to S2 COM A Address COM A COM 3 COM B COM 4 Jumpers JP16 JP20 COM 2S IRQ 232 422 Select communications mode Single ended RS232 or Differential RS422 485 TERM Terminate receiver lines in RS422 and or 485 mode BIAS Apply bias to receiver lines in RS485 mode RTS A B Use manual RTS RS485 transceiver control For port A or B AUTO A B Use automatic RTS RS485 transceiver control For port A or B ECHO A B Locally echo characters 2 wire RS485 only For port A or B 18 Manual COM 2S Chapter 4 Address Selection The COM 2S base address can be selected anywhere within an I O address range 100 3F8 hex providing thatthe address does not overlap with other functions Ifin doubt refer to the table below for a list of standard address assignments The primary and secondary binary synchronous communication ports are supported by the Operating System The FINDBASE base address locator program provided with your card will assist you to select a base address that will
24. o set the Line Control Register at Base Address 3 This register defines word length stop bits parity and the DLAB Bits 0 and 1 control word length and allow word lengths from 5 to 8 bits Bit settings are extracted by subtracting 5 from the desired word length Bit 2 determines the number of stop bits There can b ither one or two stop bits If Bit 2 is set to 0 there will be one stop bit If Bat 2 ES set to 1 there will be two stop bits Bits 3 through 6 control parity and break enable They are not commonly used for communications and should be set to zeroes Bit 7 is the DLAB discussed earlier It must be set to zero after the divisor is loaded or else there will be no communications The C command to set the UART for an 8 bit word no parity and one stop bit is outportb BASEADDR 3 0x03 The third step of the initialization sequence is to setthe Modem Control Register at Base Address 4 Bit 1 is the Request to Send RTS control bit This bit should be left low until transmission time Note When operating in the automatic RS 485 mode the state of this bit is not significant Bits 2 and 3 are 23 Manual COM 2S user designated outputs Bit 2 may be ignored on this card Bit 3 is used to enable interrupts and should be set high if an interrupt driven receiver is to be used The final initialization step is to flush the receiver buffers You do this with two reads from the receiver buffer at Base Address
25. oad across the input for RS422 mode and across the transmit receive input output for RS485 operation In RS485 operations where there are multiple terminals only the RS485 ports at each end of the network should have terminating resistors as described above Also for RS485 operation there must be a bias on the RX and RX lines If the COM 2S card is to provide that bias install jumpers at the locations labeled BIAS 5V BIAS Iko Ra TERM 1200 0 1 uF Rx 1k Q BIAS 5V Figure 3 1 Simplified Termination Schematic 15 Manual COM 2S Data Cable Wiring When two pin numbers are joined together with a amp those pins are Cable wired together in the external cable Jumpers Signal 232 x5 DCD RX RS422 485 Simplex 422 x5 Rx 2 wire Receive Only Rx Simplex 422 x5 Tx 2 wire Transmit Only Tx Half Duplex 422 x5 AUTO orRTS Rx 8 Tx 2 Wire no echo TKA 8 Rx Half Duplex 422 x5 ECHO AUTO or RTS 2 Wire with echo Full Duplex 422 x5 Txt 4 Wire Tx Rx Preferred RS485 mode 6 Manual COM 2S Card 1 Card 2 Rx 4 4 lt TRx Tx 3 3 Tx 2 2 lt gt as Rx 9 9 Interrupts In addition to standard interruptlevels IRQ2 through IRQ7 the COM 2S also supports higher interrupts IRQ10 through IRQ15 Except IRQ 13 reserved by other hardware Select the desired level by installin
26. settings 4 ReadFile and WriteFile for accessing a port See the documentation for your chosen language for details Under DOS the process is very different The remainder of this chapter describes DOS programming Initialization Initializing the chip requires knowledge of the UART s register set The first step is to set the baud rate divisor You do this by first setting the DLAB Divisor Latch Access Bit high This bit is Bit 7 at Base Address 3 In C code the call would be outportb BASEADDR 3 0x80 You then load the divisor into Base Address 0 low byte and Base Address 1 high byte The following equation defines the relationship between baud rate and divisor desired baud rate crystal frequency 32 divisor 22 Manual COM 2S On the COM 2S card acrystal frequency of 3 6864 MHz is divided by 2 before application to the UART Below is a table for the popular divisor frequencies Baud Divisor Notes Max Diff Cable Length Rate 4000 ft 4000 ft 4000 ft 4000 ft 1200 eS 4000 ft These are theoretical maximums based on typical conditions and good quality cables based on the ElA 485 and ElA 422 standard for balanced differential drivers RS 232 communication lines have a maximum length of 50 feet regardless of speed Table 5 1 Baud Rate Divisor Values In C the code to set the chip to 9600 baud is outportb BASEADDR 0x0C outportb BASEADDR 1 0 The second initializing step is t
27. ter supply a bias voltage to ensure a known zero state when all transmitters are off Also receiver inputs at each end of the network should be terminated to eliminate ringing The COM 2S supports these options by means of jumpers on the card See Chapter 3 Option Selection for more details COM Port Compatibility Type 16550 UARTs are used as the Asynchronous Communication Element ACE which include a 16 byte transmit receive buffer to protect against lost data in multitasking operating systems while maintaining 100 compatibility with the original IBM serial port However the COM 2S card is not restricted to the standard DOS addresses of COM1 COM4 Continuous address selection is available anywhere within the I O address range 000 to 3F8 hex and our FINDBASE program will scan I O Bus memory mapped addresses in your computer for available addresses that can be used by COM 2S withoutconflict with other computer resources A crystal oscillator is located on the card This oscillator ensures precise selection of baud rate from 50 to 115 200 with the standard crystal oscillator Other crystals for higher baud rate ability are available upon special order If your COM 2S is so modified then there will be an addendum sheet in the front of this catalog The driver receiver used the 75ALS180 is capable of driving extremely long communication lines at high baud rates It can drive up to 60 mA on balanced lines and receive inputs as low as 200 m
28. utput Voltage unloaded Driver Output Voltage loaded jumpers in Driver Output Resistance 500 Driver Output Short Circuit Current 150 mA Driver Output Rise Time 10 unit interval Receiver Sensitivity 200 mV Receiver Common Mode Voltage Range 7V Receiver Input Resistance 4KQ Table A 2 RS422 Specification Summary To prevent signal reflections in the cable and to improve noise rejection in both the RS422 and RS485 mode the receiver end of the cable should be terminated with a resistance equal to the characteristic impedance of the cable The exception is when the line is driven by an RS422 driver that is never tristated or disconnected from the line In this case the driver provides a low internal impedance that terminates the line at that end Note You do not have to add a terminator resistor to your cables when you use the COM 2S card Termination resistors for the RX and RX lines are provided on the card and are placed in the circuit when you install the TERM jumpers Moreover installing the BIAS jumpers properly biases these lines See the Option Selection section of this manual RS485 Data Transmission The RS485 Standard allows a balanced transmission line to be shared in a party line mode As many as 32 driver receiver pairs can share a two wire party line network Many characteristics of the drivers and receivers are the same as in the RS422 Standard One difference is that the common mode voltage limit is ext
29. ya ACCES I O PRODUCTS INC 10623 Roselle Street San Diego CA 92121 858 550 9559 e Fax 858 550 7322 contactus accesio com www accesio com MODEL COM 2S USER MANUAL FILE MCOM 2S C3d Notice The information in this document is provided for reference only ACCES does not assume any liability arising out of the application or use of the information or products described herein This document may contain or reference information and products protected by copyrights or patents and does not convey any license under the patent rights of ACCES nor the rights of others IBM PC PC XT and PC AT are registered trademarks of the International Business Machines Corporation Printed in USA Copyright 1995 2006 by ACCES l O Products Inc 10623 Roselle Street San Diego CA 92121 All rights reserved 2 Manual COM 2S Warranty Prior to shipment ACCES equipment is thoroughly inspected and tested to applicable specifications However should equipment failure occur ACCES assures its customers that prompt service and support will be available All equipment originally manufactured by ACCES which is found to be defective will be repaired or replaced subject to the following considerations Terms and Conditions If a unitis suspected of failure contact ACCES Customer Service department Be prepared to give the unit model number serial number and a description of the failure symptom s We may suggest some simple tests to confirm th
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