Black Box RS-422 User's Manual
Contents
1. RS 422 485 SERIAL INTERFACE PLUS 4 PORT E ru lt rz Figure 3 7 Headers J1D J4D RS 485 Auto Enabled with Echo E ru lt rz Figure 3 8 Headers J1D J4D RS 485 RTS Enabled with No Echo RS 422 485 SERIAL INTERFACE PLUS 4 PORT E ru lt rz Figure 3 9 Headers J1D J4D RS 485 RTS Enabled with Echo 3 7 Line Termination Typically each end of the RS 485 bus must have line terminating resistors RS 422 terminates at the receive end only A 120 ohm resistor is across each RS 530 422 485 input in addition to a 1 Kohm pull up pull down combination that bias the receiver inputs Headers JIE through J4E allow the user to customize this interface to their specific requirements Each jumper position corresponds to a specific portion of the interface If multiple Serial Interface Plus adapters are configured in a RS 485 network only the boards on each end should have jumpers T P and P ON Refer to the table on the next page for each position s operation LIL OLI TT A T Figure 3 10 Headers J1E J4E Line Termination RS 422 485 SERIAL INTERFACE PLUS 4 PORT Table 3 4 Jumper Functions Function P Adds or removes the 1 Kohm pull down resistor in the RS 422 RS 485 receiver circuit Receive data only Adds or removes the 1 Kohm pull up resistor in the RS 422 RS 485 receiver circuit Receive data only T Adds or removes the 120 ohm termination L C2. RS 422 485 SERIAL INTERFACE PLUS 4 PORT 5 Troubleshooting Two Serial Utility Diskettes are supplied with the adapter and will be used in the troubleshooting procedures By using this diskette and following these simple steps most common problems can be eliminated If you still cannot solve your problem call Black Box technical support at 724 746 5500 1 Identify all I O adapters currently installed in your system This includes your on board serial ports controller cards sound cards etc The I O addresses used by these adapters as well as the IRQ if any should be identified 2 Configure your RS 422 485 Serial Interface Plus Card so that there is no conflict with currently installed adapters No two adapters can occupy the same I O address 3 Make sure the adapter is using a unique IRQ While the adapter does allow the sharing of IRQs many other adapters such as SCSI adapters and on board serial ports do not The IRQ is typically selected via an on board header block Refer to the section on Card Setup for help in choosing an I O address and IRQ 4 Make sure the adapter is securely installed in a motherboard slot 5 Use the supplied diskette and User Manual to verify that the adapter is configured correctly The supplied diskette contains a diagnostic program SSD that will verify if an adapter is configured properly This diagnostic program is written with the user in mind and is easy to use Refer to the REA
3. Corporation All rights reserved 1000 Park Drive Lawrence PA 15055 1018 724 746 5500 Fax 724 746 0746
4. RS 422 485 SERIAL INTERFACE PLUS 4 PORT Appendix A Connector Pin Assignments 27 Appendix B Board Layout 29 Appendix C Electrical Interface 80 Appendix D Asynchronous Communications 31 RS 422 485 SERIAL INTERFACE PLUS 4 PORT 1 Specifications Communication Chip IC058C 16750 UART IC183C 16950 UART Maximum Distance 4000 ft 1219 2 m Operation 2 or 4 wire Protocol Asynchronous Speed IC058C Up to 460 8 kbps IC183C 460 8 kbps and above Connectors 1 DB37 male 4 DB9 male on included cable CE Approval The unit is CE approved Manufacturing IPC 610 A Class III standards are adhered to with an 0 1 visual A Q L and 100 Functional Testing This printed circuit board is built to U L 94V0 rating and is 100 electrically tested This printed circuit board is solder mask over bare copper or solder mask over tin nickel MTBF Greater than 150 000 hours calculated Temperature Operating 32 to 122 F 0 to 50 C Storage 4 to 158 F 20 to 70 C Humidity 10 to 90 relative humidity noncondensing Power From PC bus 600 ma 5 VDC Size Half card 4 2 H x 3 9 W 8 D 10 7 x 9 9 x 20 3 cm RS 422 485 SERIAL INTERFACE PLUS 4 PORT 2 Introduction 2 1 Overview The RS 422 485 Serial Interface Plus 4 Port provides the PC with four additional RS 422 485 serial port
5. 5 SERIAL INTERFACE PLUS 4 PORT Table 3 2 Address Selection Table Address Selected 1 2 3 4 5 280 29F Off On Off On On 2A0 2BF Off On Off On Off 380 39F Off Off Off On On 1A0 1BF On Off Off On Off 2E0 2FF Off On Off Off Off Figure 3 1 shows the correlation between the DIP switch setting and the address bits used to determine the base address In the example below address 2E0 is selected as a base Address 2E0 in binary is XX 10 111X XXXX where X a non selectable address bit Figure 3 1 DIP Switch Setting RS 422 485 SERIAL INTERFACE PLUS 4 PORT Table 3 3 Port to Connector Table Port Connector Location Address Example Base 2E0 Base 0 2E0 2E7 Base 8 2E8 2EF Base 16 2F0 2F7 Base 24 2F8 2FF 3 2 Jumper Selections For ease of configuration the headers are grouped by port Port 1 headers have a J1 prefix Port 2 headers have the J2 prefix etc For example the header that controls the Port 1 IRQ selection is J1B the header that controls the Port 2 IRQ selection is J2B Information for configuring the adapter is printed directly on the Card This is particularly useful in field re configuration 3 3 IRQ Selection Headers J1B through J4B select the interrupt request for each serial port If COMI is selected the corresponding jumper must be on the IRQ4 setting If COM2 is selected the corresponding jumper must be on IRQ3 NOTE Most communications software applications defaul
6. 6950 UART which features a 128 byte FIFO for even better performance 2 4 1 FEATURES Automatic RS 485 driver enable disable allows card to appear to be RS 232 requiring no additional drivers PAL option allows for unique OEM address selection e Shareable IRQs allow more than one port to share a single IRQ IRQs 2 9 7 10 11 12 15 supported 16750 buffered UARTs IC058C or 16950 UARTs IC183C 16 Bit address decode allows for easier integration Speeds up to 460 8 kbps available Multiple clocking modes ensure compatibility with existing software products RS 422 485 SERIAL INTERFACE PLUS 4 PORT 2 4 2 MODEM CONTROL SIGNALS Some software packages require the use of modem handshake signals such as CTS or DCD Refer to your application software manual to determine the requirements for modem control signals If no requirements are mentioned a safe configuration is to tie DTR to DSR and DCD and tie RTS to CTS This configuration will typically satisfy the modem control signal requirements for most communications software 2 4 3 INTERRUPTS A good analogy of a PC interrupt would be a phone ringing The phone bell is a request for us to stop what we are currently doing and take up another task speak to the person on the other end of the line This is the same process the PC uses to alert the CPU that a task must be performed The CPU upon receiving an interrupt makes a record of what the proce
7. DME file on the supplied diskette for detailed instructions on using SSD RS 422 485 SERIAL INTERFACE PLUS 4 PORT 6 The following are known I O conflicts The 278 and 378 settings may conflict with your printer I O adapter 3B0 cannot be used if a Monochrome adapter is installed e 3F8 3FF is typically reserved for COMI e 2F8 2FF is typically reserved for COM2 e 3E8 3EF is typically reserved for COM3 e 2E8 2EF is typically reserved for COM4 7 Please refer to your included diskette for any post production manual updates and application specific information 8 Always use the included diagnostic software when troubleshooting a problem This will eliminate the software issue from the equation RS 422 485 SERIAL INTERFACE PLUS 4 PORT Appendix A Connector Pin Assignments Table A 1 DB9 Pin Assignments Signa Name Pin Mode 6 RTS Request to Send Positive Output RTS Request to Send Negative Output RX Receive Data Positive 1 Input RX Receive Data Negative 2 Input 9 CTS Clear to Send Positive Input CTS Clear to Send Negative Input RS 422 485 SERIAL INTERFACE PLUS 4 PORT Table A 2 DB37 Pin Assignments Qz a bg un A per Qz prr lt az rr V2 wa lt N c cu n Qz Board Layout Appendix B C12 JxA INT MODE SELECT JxC CLOCK N NORMAL INT MODE DIV1 CLOCK S SHARED INT MODE D
8. IV2 CLOCK U9 E aie SHARED WITH RESISTOR DIV4 CLOCK JxB INT SELECT E C5 ve DC u CD C7 U11 D74HC04 PORT 1 Jix PORT2 J2x PORT3 J3x PORT4 J4x 3 4 5 6 7 910111215 PAL D2 N SM R3 J2B DIV1 a 16550 PORT1 16550 PORT2 us 74H0125 222228005 us Hs ue EJ us CD cto cs SWITCH8DIP swj EE d 5 ika 34567 910111215 JAI Ds NSM DIV1 DIV DIV 5 A R N P2 P1 RP3 n uibzasz4 U20751 JA RP1 MACH215 MACH215 RH R6 C14 JA Re SDL R7 J2E vole EIS a cc REZ U15975174 J3B RSR REMOVE ALL JUMPERS ve 3450791011125 SSS Asses AT ATS ENABLE J4A D4 aaa RS485 NE NO ECHO P J4B C L 5 L 315679010215 SSS 16550PORT3 16550 PORTA E 7415244 TALS245 5 aaa c1 JxE JUMPER SETTINGS P PULL UP DOWN ENABLE T TERMINATION ENABLE L CONNECT RX TO TX Cravo tr 15 Fr400 TT 5v Board Layout 1 B igure F Appendix C Electrical Interface RS 422 The RS 422 specification defines the electrical characteristics of balanced voltage digital interface circuits RS 422 is a differential interface that defines voltage levels and driver receiver electrical specifications On a differential interface logic levels are defined by the difference in voltage between a pair of outputs or inputs In contrast a single ended interface for example RS 232 defines the logic levels as the difference i
9. Please refer to the WINDOWS sub directory on the Serial Utilities Diskette for help files and current information on the installation of the Card in thisoperating environment 4 1 2 WINDOWS 95 98 USERS For the ISA card run setup on disk two of the Serial Utilities Diskettes before installing the card Make note of the resources that Windows assigns the adapter and set the adapter to match those resources Power down the computer and install the adapter as described in Section 4 2 If you wish to change any resources assigned to the adapter refer to the help file installed in the Black Box folder in the Start Programs menu 4 1 3 WINDOWS NT For the ISA card run setup on disk two of the Serial Utilities Diskettes before installing the card After installing the software refer to the help file that automatically comes up for installation instructions RS 422 485 SERIAL INTERFACE PLUS 4 PORT 4 2 Hardware Installation The RS 422 485 Serial Interface Plus Card can be installed in any of the PC expansion slots The Card contains several jumper straps for each port that you must set for proper operation 1 Turn off PC power Disconnect the power cord 2 Remove the PC case cover 3 Locate an available slot and remove the blank metal slot cover 4 Gently insert the Card into the slot Make sure that the Card is seated properly 5 Replace the screw 6 Replace the cover 7 Connect the power cord Installation is complete
10. S BLACK BOX MO O RE RR RN JUNE 2000 ICO58C IC183C RS 422 485 Serial Interface Plus 4 Port O NY lo AAA APA AAA cmm o AIN 3b o w VE EE NE NE NE NS boo NE VE D os Ex x X SS LLL LLL LLLLLLI CUSTOMER Order toll free in the U S 24 hours 7 A M Monday to midnight Friday 877 877 BBOX SUPPORT FREE technical support 24 hours a day 7 days a week Call 724 746 5500 or fax 724 746 0746 INFORMATION Mail order Black Box Corporation 1000 Park Drive Lawrence PA 15055 1018 Web site www blackbox com E mail info blackbox com RS 422 485 SERIAL INTERFACE PLUS 4 PORT TRADEMARKS All applied for and registered trademarks are the property of their respective owners Any trademarks mentioned in this manual are acknowledged to be the property of the trademark owners EMC Directive Statement Products bearing the CE label fulfill the requirements of the EMC directive 89 336 EEC and of the low voltage directive 73 23 EEC issued by the European Commission To obey these directives the following European standards must be met e EN55022 Class A Limits and methods of measurement of radio interference characteristics of information technology equipment EN50082 1 Electromagnetic compatibility Generic immunity standard Part 1 Residential commercial and light industry EN60950 IEC950 Safety of information technology equipment i
11. an be cabled in two ways two wire and four wire mode Two wire mode does not allow for full duplex communication and requires that data be transferred in only one direction at a time For half duplex operation the two transmit pins should be connected to the two receive pins Tx to Rx and Tx to Rx Four wire mode allows full duplex data transfers RS 485 does not define a connector pin out or a set of modem control signals RS 485 does not define a physical connector RS 422 485 SERIAL INTERFACE PLUS 4 PORT Appendix D Asynchronous Communications In serial data communications individual bits of a character are transmitted consecutively to a receiver that assembles the bits back into a character Data rate error checking handshaking and character framing start stop bits are pre defined and must correspond at both the transmitting and receiving ends Asynchronous communications is the standard means of serial data communication for PC compatibles and PS 2 computers The original PC was equipped with a communication or COM port that was designed around an 8250 Universal Asynchronous Receiver Transmitter UART This device allows asynchronous serial data to be transferred through a simple and straightforward programming interface Character boundaries for asynchronous communications are defined by a starting bit followed by a pre defined number of data bits 5 6 7 or 8 The end of the character is defined by the transmissi
12. cheme that allows it to be completely compatible with older four port RS 422 485 interface adapters and provide for the ability to select address combinations more commonly used The first addressing scheme allows the Card to select the addresses for its ports from a table of available address combinations Table 3 1 shows the addressing combinations available If different address combinations are required please contact Technical Support about a custom PAL option RS 422 485 SERIAL INTERFACE PLUS 4 PORT Table 3 1 Available Address Combinations Switch 6 Switch 7 Switch 8 Port 1 Port Port3 Port 4 ff 3F8 2F8 3E8 2E8 n 2F8 3E8 2E8 2E0 ff 3E8 2E8 280 288 n 500 508 510 518 ff 580 588 590 598 n 1500 1508 1510 1518 On On O On Off O On Off O Off On O Off On O Off Off O Off Off Off 3220 32288 4220 4228 On On On Addresses set up by switches 1 5 NOTE Each COM port in the system should have a unique address Typically COM 1 COMA addresses are 3F8 2F8 3E8 and 2E8 Hex Refer to Chapter 5 for common address contentions The second mode of address selection provides the compatibility mode In this mode the DIP switch sets the base address and the adapter occupies 32 consecutive I O locations Table 3 2 describes the location of each port and its relationship to the other ports NOTE For switches 1 5 to become active switches 6 7 and 8 must be set in the On or Up position RS 422 48
13. lication with existing standard RS 232 software drivers Headers J1D through J4D are used to control the RS 485 mode functions for the driver circuit The selections are RTS enable silk screen RT or Auto enable silk screen AE The Auto enable feature automatically enables disables the RS 485 interface The RTS mode uses the RTS modem control signal to enable the RS 485 interface and provides backward compatibility with existing software products Position 3 silk screen NE of J1D through J4D is used to control the RS 485 enable disable functions for the receiver circuit and determine the state of the RS 422 485 driver The RS 485 Echo is the result of connecting the receiver inputs to the transmitter outputs Every time a character is transmitted it is also received This can be beneficial if the software can handle echoing using received characters to throttle the transmitter or it can confuse the system if the software does not To select the No Echo mode select silk screen position NE For RS 422 530 449 compatibility remove the jumpers at J1D through J4D Examples on the following pages describe all of the valid settings for J1D J4D RS 422 485 SERIAL INTERFACE PLUS 4 PORT 3 6 Interface Mode Examples J1D J4D LL tz Figure 3 5 Headers J1D JAD RS 422 E ru lt rz Figure 3 6 Headers J1D J4D RS 485 Auto Enabled with No Echo
14. mpatible adapter in a bus you should only have one port set to M Figure 3 4 shows two ports sharing a single IRQ Figure 3 4 Header J1A amp J2A Shared IRQ Mode Set the jumper to S if you are using more than one Card in a bus or to completely remove the pull down resistor for hardware compatibility Setting the adapter in this configuration when it is not accompanied by a pull down resistor will prevent the ports from triggering an interrupt RS 422 485 SERIAL INTERFACE PLUS 4 PORT 3 5 RS 485 Enable Modes RS 485 is ideal for multi drop or network environments RS 485 requires a tri state driver not dual state that will allow the electrical presence of the driver to be removed from the line The driver is in a tristate or high impedance condition when this occurs Only one driver may be active at a time and the other driver s must be tri stated The output modem control signal Request To Send RTS is typically used to control the state of the driver Some communication software packages refer to RS 485 as RTS enable or RTS block mode transfer One of the unique features of the Serial Interface Plus Card is the ability to be RS 485 compatible without the need for special software or drivers This ability is especially useful in Windows Windows NT and OS 2 environments where the lower level 1 0 control is abstracted from the application program This ability means that you can effectively use the Card in an RS 485 app
15. n voltage between a single signal and a common ground connection Differential interfaces are typically more immune to noise or voltage spikes that may occur on the communication lines Differential interfaces also have greater drive capabilities that allow for longer cable lengths RS 422 is rated up to 10 Megabits per second and can have cabling 4000 feet 1219 m long RS 422 also defines driver and receiver electrical characteristics that will allow 1 driver and up to 32 receivers on the line at once RS 422 signal levels range from 0 to 5 volts RS 422 does not define a physical connector RS 485 RS 485 is backward compatible with RS 422 however it is optimized for partyline or multi drop applications The output of the RS 422 485 driver is capable of being Active enabled or Tri State disabled This capability allows multiple ports to be connected in a multi drop bus and selectively polled RS 485 allows cable lengths up to 4000 feet 1219 m and data rates up to 10 Megabits per second The signal levels for RS 485 are the same as those defined by RS 422 RS 485 has electrical characteristics that allow for 32 drivers and 32 receivers to be connected to one line This interface is ideal for multi drop or network environments RS 485 s tri state driver not dual state will allow the electrical presence of the driver to be removed from the line Only one driver may be active at a time and the other driver s must be tri stated RS 485 c
16. ncluding electrical business equipment RS 422 485 SERIAL INTERFACE PLUS 4 PORT Contents Li Sp cifications sister ebPR a Rae DERE ak tte 7 2 Introduction seen Me a eS ERES tt des ERR 8 2 1 OVE EW a o kar tte pbi RA Baer E S ed 8 2 2 What s Included terepinen vate rre nte 8 2 3 Factory Default Settings 8 2 4 Technical Description 9 2 4 L Beatures s bett ete e ees 9 2 4 2 Modem Control Signals 10 2 4 5 TIterruptsussc en nes tee RURE eet ons 10 2 4 4 Why Use an ISP 10 Bc Card Set a cae eet ec Gs ratte dhe Pals um eot ele MOLES 11 3 1 Address Selection 11 3 2 Jumper Selections 14 3 3 IRO Selection iii ras DIRE RR tent 14 3 4 Interrupt Modes 15 3 5 RS 485 Enable Modes 16 3 6 Interface Mode Examples JID J4D 18 3 7 Line Termination 20 5 9 Glock MOG6S cere ut nes PGE a Mow ee Wile di be ew 21 4 Installati fk 5v sn das 24 4 1 Software Installation 24 LE Windows 3 IX 5 secs teme Ae ee a Es 24 4 1 2 Windows 95 98 24 4 1 5 Windows NT siet eT RI den do ete A 24 4 2 Hardware Installation 24 Ds Troubleshooting zi a l ere mem uusha iaa de 26
17. on of a pre defined number of stop bits usual 1 1 5 or 2 or Even Idle state of Remain idle or line Unused next start bit 3 5 to 8 Data Bits gt 1 y ras NNNM 3 1 1 1 1 1 1 1 1 P i BITI a 0 mm rm mium m Jssdesdesdssde sde n ses lt gt 14 1 5 1 Figure D 1 Asynchronous Communications Bit Diagram RS 422 485 SERIAL INTERFACE PLUS 4 PORT An extra bit used for error detection is often appended before the stop bits This special bit is called the parity bit Parity is a simple method of determining if a data bit has been lost or corrupted during transmission There are several methods for implementing a parity check to guard against data corruption Common methods are called E ven Parity and O dd Parity Sometimes parity is not used to detect errors on the data stream This is refereed to as N o parity Because each bit in asynchronous communications is sent consecutively it is easy to generalize asynchronous communications by stating that each character is wrapped framed by pre defined bits to mark the beginning and end of the serial transmission of the character The data rate and communication parameters for asynchronous communications have to be the same at both the transmitting and receiving ends The communication parameters are baud rate parity number of data bits per character and stop bits for example 9600 N 8 1 BLACK BOX O Copyright 2000 Black Box
18. onnects the TX to RX for RS 485 two wire operation L Connects the TX to RX for RS 485 two wire operation 3 8 Clock Modes The Serial Interface Plus Card employs a unique clocking option that allows the user to select from divide by 4 divide by 2 and divide by 1 clocking modes These modes are selected at Headers J1C through J4C To select the baud rates commonly associated with COM ports 2400 4800 9600 19 2 and so on up to 115 2 kbps place the jumper in the divide by 4 mode silk screen DIV4 RS 422 485 SERIAL INTERFACE PLUS 4 PORT IL mie Y NA Y 2 Q Aa Figure 3 11 Clocking Mode Divide By 4 To double these rates up to a maximum rate for 230 4 kbps place the jumper in the divide by 2 silk screen DIV2 position ON Y ODO Figure 3 12 Clocking Mode Divide By 2 To select the maximum data rate 460 8 kbps place the jumper in the divide by 1 silk screen DIVI position RS 422 485 SERIAL INTERFACE PLUS 4 PORT LIL L gt gt gt OOO Figure 3 13 Clocking Mode Divide By 1 RS 422 485 SERIAL INTERFACE PLUS 4 PORT A Installation IMPORTANT You MUST set up the operating system BEFORE you physically install the Card 4 1 Software Installation If you are installing an ISA adapter in DOS OS 2 or QNX please refer to the appropriate directory on one of the Serial Utilities Disks for instructions 4 1 1 WINDOWS 3 1x
19. s for terminals modems printers etc The Card is RS 485 compatible without special software or drivers This ability is especially useful in Windows Windows NT and OS 2 environments where the lower level I O control is abstracted from the application program This ability means that you can effectively use the Card in an RS 485 application with existing standard RS 232 software drivers 2 2 What s Included The Card is shipped with the following items If any of these items are missing or damaged contact the supplier e RS 422 485 Serial Interface Plus 4 Port Card DB37 to four DB9 Spider Cable e 2 serial utility software diskettes 1 for 32 bit Windows 1 for DOS and Windows 3 1x This User s Manual 2 3 Factory Default Settings The factory default settings are as follows Table 2 1 Factory Default Settings Port Base Address IRQ Electrical Specifications Port 1 3F RS 422 F 8 4 E8 3 Port 4 2 RS 422 RS 422 485 SERIAL INTERFACE PLUS 4 PORT To install the Card using factory default settings refer to Chapter 4 Installation For your reference record installed Card settings below Table 2 2 Your Installed Card Settings Port Base Address Electrical Specifications 2 4 Technical Description The IC058C Card uses the 16750 UART This chip features programmable baud rate data format and interrupt control and a 16 byte input and output FIFO The IC183C card uses the 1
20. ssor was doing at the time and stores the information in the stack this allows the processor to resume its predefined duties after the interrupt is handled exactly where it left off Every main subsystem in the PC has its own interrupt frequently called an IRQ short for Interrupt ReQuest 2 4 4 WHY USE AN ISP An Interrupt Status Port ISP is a read only 8 bit register that sets a corresponding bit when an interrupt is pending Port 1 interrupt line corresponds with Bit DO of the status port Port 2 with D1 etc The use of this port means that the software designer now only has to poll a single port to determine if an interrupt is pending The ISP is at Base 7 on each port Example Base 280 Hex Status Port 287 28F etc The RS 422 485 Serial Interface Plus Card will allow any one of the available locations to be read to obtain the value in the status port All four status ports on the Card are identical so any one of the four can be read Example This indicates that Port 2 has an interrupt pending Bit Position 7 6 5 4 3 2 1 Value Read 0 0 0 0 0 0 1 oo RS 422 485 SERIAL INTERFACE PLUS 4 PORT 3 Card Setup The RS 422 485 Serial Interface Plus 4 Port Card has several jumper straps which must be set for proper operation 3 1 Address Selection Each port on the Card occupies eight consecutive I O locations A DIP switch is used to set the base address for these locations The Card has a unique addressing s
21. t COM3 to IRQ4 and COM4 to IRQ3 This requires the sharing of interrupts between COM1 and COM3 and between COM2 and COMA4 While this is the default it is not always the best setting Check your software configuration instructions to determine the most appropriate IRQ selection RS 422 485 SERIAL INTERFACE PLUS 4 PORT 3 4 5 6 7 9 10 11 12 15 Figure 3 2 Headers J1B J4B IRQ Selection Any two or more ports can share a common IRQ by placing the jumpers on the same IRQ setting and setting the appropriate selections at JIA through J4A Consult your particular software for IRQ selection If no interrupt is desired remove the jumper 3 4 Interrupt Modes Headers J1A through J4A select the interrupt modes for each port Each port must be set in the correct mode to ensure proper operation N indicates the N ormal single interrupt per port mode S indicates the S hared interrupt mode which allows more than one port to access a single IRQ M indicates the inclusion of a 1 Kohm pull down resistor required on one port when sharing interrupts N S M Figure 3 3 Header J1A Normal IRQ Mode RS 422 485 SERIAL INTERFACE PLUS 4 PORT Set the jumpers to S for shared interrupt mode on all blocks sharing an IRQ except one Set that port block for M This provides the pull down resistor circuit that makes sharing IRQs possible If you are using more than one Serial Interface Plus Card or a co
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