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National Instruments GPIB-COM, User Manual

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© National Instruments Corporation

5-1

GPIB-COM User Manual

Section Five
Programming the GPIB-COM

                                                                                                                                                            

 

This section presents a description of the GPIB-COM Serial Port Emulator registers and
information on programming the GPIB-COM.  You need to use this section only if you are
writing your own serial port device driver.

The GPIB-COM Registers

IBM's serial adapter is a plug-in card for the PC that handles RS-232 communication.  The main
component of the adapter is an INS8250 Asynchronous Communications chip or its equivalent,
which is controlled by programming a set of registers on the I/O channel.  The names of these
registers and their I/O addresses are given in Table 5-1.  Each register is located at a certain offset
from the base address of the board.  The addresses are given with an X for the first digit and a Y
for the second digit, where XY=3F for COM1 (base address 3F8), XY=2F for COM2 (base
address 2F8), XY=3E for COM3 (base address 3E8), and XY=2E for COM4 (base address
2E8).  Notice that sometimes two registers share the same I/O address.  The DLAB bit (bit 7 of
the Line Control Register) determines which register will respond when these addresses are
accessed.

Note: Throughout this section, the term set will be used to mean that a bit is a logical 1, and clear

will mean that the bit is a logical 0.

Table 5-1.  GPIB-COM Registers

I/O Address

Offset from

Register

Type

XY=3F for COM1

Base Address

XY=2F for COM2
XY=3E for COM3
XY=2E for COM4

Transmitter Holding Register 

write

XY8 (DLAB=0)

0

Receive Buffer Register

read

XY8 (DLAB=0)

0

Divisor Latch LSB Register

read/write

XY8 (DLAB=1)

0

Divisor Latch MSB Register

read/write

XY9 (DLAB=1)

1

Interrupt Enable Register

read/write

XY9 (DLAB=0)

1

Interrupt Identification Register

read

XYA

2

Line Control Register

read/write

XYB

3

Modem Control Register

read/write

XYC

4

Line Status Register

read

XYD

5

Modem Status Register

read

XYE

6

The following pages describe the functions of each register on the serial adapter and on the GPIB-
COM.  For a more complete description of the serial adapter, refer to the IBM Options and
Adapters Manual.

Summary of Contents for GPIB-COM

Page 1: ... Copyright 1989 1991 National Instruments Corporation All Rights Reserved GPIB COM User Manual June 1990 Edition Part Number 320197 01 ...

Page 2: ...National Instruments Corporation 6504 Bridge Point Parkway Austin TX 78730 5039 512 794 0100 800 IEEE 488 toll free U S and Canada Technical support fax 512 794 5678 ...

Page 3: ...wner All items returned to National Instruments for repair must be clearly marked on the outside of the package with an RMA number No other warranty is expressed or implied National Instruments shall not be liable for consequential damages Contact National Instruments for more information Important Notice The material in this manual is subject to change without notice National Instruments assumes ...

Page 4: ...ation However the chances of interference are much less if the equipment is used according to this instruction manual If the equipment does cause interference to radio or television reception which can be determined by turning the equipment on and off one or more of the following suggestions may reduce or eliminate the problem Operate the equipment and the receiver on different branches of your AC...

Page 5: ...he functional components of the GPIB COM Section Four Running Diagnostic Tests describes how to run the diagnostic tests that are shipped with the GPIB COM Section Five Programming the GPIB COM presents a description of the GPIB COM Serial Port Emulator registers and information on programming the IBM serial adapter Appendix A Specifications lists the specifications of the GPIB COM board Appendix ...

Page 6: ...reviations are used in the text of this manual is less than or equal to is greater than or equal to plus or minus A ampere C Celsius hex hexadecimal in inch I O input output kbyte 1000 bytes m meter Mbyte megabyte MHz megahertz msec millisecond r read r w read write sec second V volt VDC volts direct current w write ...

Page 7: ... COM Interface 3 1 GPIB COM Components 3 3 Address Decoding 3 3 Configuration Jumpers 3 3 INS8250A Compatible Registers 3 3 GPIB Acceptor and Source Handshaking 3 3 Mode Control Logic 3 3 Interrupt Control Logic 3 3 Direction Buffers 3 4 GPIB Transceivers 3 4 Section Four Running Diagnostic Tests 4 1 The GPIB COM Test Commands 4 1 1 printer test 4 1 2 plotter test 4 2 c change COM configuration 4 ...

Page 8: ...iline Interface Command Messages B 1 Appendix C Operation of the GPIB C 1 History of the GPIB C 1 Types of Messages C 1 Talkers Listeners and Controllers C 1 System Controller and Active Controller C 2 GPIB Signals C 2 Data Lines C 3 Handshake Lines C 3 NRFD not ready for data C 3 NDAC not data accepted C 3 DAV data valid C 4 Interface Management Lines C 4 ATN attention C 4 IFC interface clear C 4...

Page 9: ...Setting for Listen Address 10 Hex 2 6 Figure 2 6 Switch Setting for REN ON IFC OFF and SRQ OFF 2 7 Figure 3 1 Block Diagram of GPIB COM 3 2 Figure 4 1 Plotter Output 4 2 Figure C 1 GPIB Cable Connector C 3 Figure C 2 Linear Configuration of the GPIB Devices C 5 Figure C 3 Star Configuration of GPIB Devices C 6 Tables Table 2 1 IBM PC Serial Port Adapters 2 3 Table 2 2 Factory Default Settings and ...

Page 10: ...the IBM PC operating system and software It can be used to interface IEEE 488 devices to any PC software that uses the serial ports The GPIB COM has the following hardware features emulates the standard PC serial adapter interface so that no additional software is needed can be configured as either COM1 COM2 COM3 or COM4 compatible with any software using the serial ports on the IBM PC and its com...

Page 11: ...ld contain the following components Item Part Number GPIB COM interface board 180750 01 GPIB COM User Manual 320197 01 GPIB COM Diagnostic Test Diskette 420212 45 Note The GPIB COM Diagnostic Test Diskette contains the com exe diagnostic test that is described in Section Four Running Diagnostic Tests Make sure each of these items is in your kit If any item is missing contact National Instruments ...

Page 12: ...lded Cables GPIB Type X2 Cable 1 m 763061 01 GPIB Type X2 Cable 2 m 763061 02 GPIB Type X2 Cable 4 m 763061 03 In order to meet FCC emission limits for a Class B device you must use a shielded GPIB cable Operating this equipment with a non shielded cable may cause interference to radio and television reception in residential areas ...

Page 13: ...Two Configuration and Installation This section contains information on how to configure and install the GPIB COM into your system Configuration Figure 2 1 shows the locations of the GPIB COM configuration jumpers and switches Figure 2 1 GPIB COM Parts Locator Diagram ...

Page 14: ...is powered on DOS searches the serial port addresses for installed adapters It first searches 3F8 then 2F8 If only one device is installed that device is named COM1 regardless of what its I O address is If there is more than one serial device installed the first one found is assigned COM1 and the second one found is assigned COM2 Some communications software also recognizes COM3 base address 3E8 a...

Page 15: ...ry settings and optional configurations for the switches and jumpers on the GPIB COM Table 2 2 Factory Default Settings and Optional Configurations GPIB COM Default Optional Base I O Address 3F8 2F8 3E8 2E8 Interrupt Level 4 3 If you need to change the factory settings continue on If you do not need to change the factory settings skip to Installation later in this section Base I O Address and Inte...

Page 16: ...W5 W2 c COM3 Jumpers Set to Base I O Address 3E8 hex Interrupts Not Used XF8 3X8 IRQ4 XE8 2X8 IRQ3 W5 W2 d COM4 Jumpers Set to Base I O Address 2E8 hex Interrupts Not Used Figure 2 2 Possible Settings for GPIB COM Jumpers Talk Listen Modes If you are using your GPIB COM with a listen only printer or plotter you can configure the GPIB COM for a talk only mode In this mode the GPIB COM is always a T...

Page 17: ...bles REN The OFF position disables REN IFC Enables disables the Interface Clear IFC option on the GPIB COM If enabled the GPIB COM issues an IFC when it is initialized The ON position enables IFC on initialization The OFF position holds IFC unasserted SRQ Enables disables the Service Request SRQ option If enabled the GPIB COM monitors the SRQ line through the Parity Error Bit PE in the Line Status...

Page 18: ...0 hex The listen address varies with each device so check the listen address of your device and set these five bits accordingly Key side you must press down for Listen Address 10 Off 1 On 0 This side down for logic 1 This side down for logic 0 U13 used for setting REN ON IFC ON and SRQ ON 1 2 4 8 16 REN IFC SRQ 1 2 3 4 5 6 7 8 OFF Figure 2 5 Listen Address Setting for Listen Address 10 Hex ...

Page 19: ...itches and jumper settings you are ready to install the GPIB COM The following steps are general installation instructions Consult the user manual or technical reference manual of your personal computer for specific instructions and warnings 1 Turn off your computer 2 Remove the plug from its power source 3 Remove the top cover or access port to the I O channel 4 Remove the expansion slot cover on...

Page 20: ...DE command is used to set the RS 232 parameters that will be used when COM1 and COM2 are accessed through DOS Sometimes a timeout error may occur when writing through the GPIB COM to a slow device such as a printer or a plotter If this happens use the MODE command to disable the timeout function by typing MODE COM1 12 P Some software applications use the COM port baud rate setting to control the d...

Page 21: ...that uses serial ports A set of I O registers identical to those on the standard IBM serial adapter is used On the GPIB side the GPIB COM includes a limited subset of interface functions that address a GPIB device to listen when the computer sends data to the serial port and to talk when the computer is waiting to receive data from the serial port In order to be able to respond immediately to comm...

Page 22: ...gram of the GPIB COM Address Bus Interrupt Control Address Decoding INS8250A Compatible Registers IRQ3 IRQ4 AEN IOW IOR Data Bus GPIB Config Jumpers Config Jumpers PC I O Channel Direction Buffer Direction Buffer Mode Control Logic Acceptor Handshake Source Handshake GPIB Transceivers Figure 3 1 Block Diagram of GPIB COM ...

Page 23: ...NS8250A Compatible Registers The main component of an IBM PC compatible serial adapter is an INS8250A Asynchronous Communications chip or its equivalent which handles RS 232 communication The INS8250A compatible registers on the GPIB COM emulate the serial adapter registers so that the GPIB COM will operate transparently with any serial port driver GPIB Acceptor and Source Handshaking This circuit...

Page 24: ...eivers The GPIB COM is interfaced to the IEEE 488 bus by National Semiconductor 75160A and 75162A transceivers These integrated circuits are specifically designed to provide power up power down bus protection glitch free The GPIB COM counts as one IEEE 488 bus load thereby allowing an additional 14 devices to be connected before exceeding the bus loading restrictions imposed by the IEEE 488 ...

Page 25: ...TRUMENTS GPIB COM DIAGNOSTIC TESTS This program assumes the GPIB COM is configured at base address 3F8 COM1 If you reconfigured your GPIB COM you must change the address that this program uses To do this enter command c from the menu Enter one of the following commands 1 printer test 2 plotter test c change COM configuration q quit A short explanation of each command is given in the following para...

Page 26: ...KLMNOPQRSTUVWXYZ _ abcdefghi jklmnopqrstuvwxyz 0123456789 ABCDEFG HIJKLMNOPQRSTUVWXYZ _ abcdefghijklmnopqrstuvwxyz If the printer does not respond an error message appears on the screen along with a message telling you to recheck all of your connections and jumper settings If the test still fails after everything has been checked write down the error message if any and call National Instruments 2 ...

Page 27: ...nd call National Instruments c change COM configuration This command is used to change the base address of the GPIB COM to match the actual board settings If you have changed the jumper settings to something different than the default settings you must run this command When this command is selected the following menu appears This program assumes the GPIB COM is configured at base address 3F8 COM1 ...

Page 28: ...E8 and XY 2E for COM4 base address 2E8 Notice that sometimes two registers share the same I O address The DLAB bit bit 7 of the Line Control Register determines which register will respond when these addresses are accessed Note Throughout this section the term set will be used to mean that a bit is a logical 1 and clear will mean that the bit is a logical 0 Table 5 1 GPIB COM Registers I O Address...

Page 29: ...r Address XF8 DLAB bit in Line Control Register 0 7 6 5 4 3 2 1 0 D6 D5 D7 D4 D3 D2 D1 D0 W The Transmitter Holding Register contains the character to be sent to the serial output with bit 0 being the least significant and bit 7 the most significant It functions identically on the GPIB COM and the INS8250 Bit Mnemonic Description 7 0w D 7 0 Data Bits 7 through 0 ...

Page 30: ...er Address XF8 DLAB bit in Line Control Register 0 7 6 5 4 3 2 1 0 D6 D5 D7 D4 D3 D2 D1 D0 R The Receive Buffer Register contains the character received from the serial input with bit 0 being the least significant and bit 7 the most significant It functions identically on the GPIB COM and the INS8250 Bit Mnemonic Description 7 0r D 7 0 Data Bits 7 through 0 ...

Page 31: ...Register Offset from Base I O Address 1 Register Address XF9 DLAB bit in Line Control Register 1 7 6 5 4 3 2 1 0 DL14 DL13 DL15 DL12 DL11 DL10 DL9 DL8 R W The value stored in these two registers is used to determine the baud rate for serial communica tions The 16 bit number formed by the Divisor Latch LSB and MSB is divided into a 1 8432 MHz clock to produce the baud rate The Divisor Latch Registe...

Page 32: ... 4 These bits always read as 0 3r w MS Modem Status Interrupt Enable Bit This bit enables a modem status interrupt when set to logical 1 The modem status interrupt occurs when any of bits 0 through 3 of the Modem Status Register are set to logical 1 This bit is identical on the GPIB COM and the INS8250 but bits 0 through 3 of the Modem Status Register are set for different conditions as noted unde...

Page 33: ...ding register empty interrupt occurs when the INS8250 becomes ready to send another character This bit functions identically on the GPIB COM and the INS8250 0r w RDA Received Data Available Interrupt Enable Bit This bit enables a received data available interrupt when set The received data available interrupt occurs when a character is received from the serial input and stored in the Receive Buffe...

Page 34: ...0 Bit Mnemonic Description 7 3r 0 Reserved Bits 7 through 3 These bits always read as 0 2 1r ID 1 0 Identify Interrupt Register Bits These two bits identify the interrupt that is pending If more than one interrupt is pending only the one with the highest priority is identified The types and priorities are given in Table 5 2 Table 5 2 Interrupt Types and Priorities Bit 2 Bit 1 Type of Interrupt Pri...

Page 35: ...e Divisor Latch LSB and MSB and cleared to access the Transmitter Holding Register the Receive Buffer Register and the Interrupt Enable Register This bit functions identically on the GPIB COM and the INS8250 6r w SBRK Set Break Control Bit When set this bit causes the SOUT line of the serial cable to be forced to a logical 0 state This bit is ignored by the GPIB COM 5r w STP Stick Parity Bit When ...

Page 36: ...nored by the GPIB COM 2r w STB Stop Bit Control Bit This bit controls the number of stop bits sent and verified by the INS8250 If this bit is set two stop bits will be used If this bit is clear one stop bit will be used This bit is ignored by the GPIB COM 1 0r w WL 1 0 Word Length Select Bits These two bits set the length of the words sent or received according to Table 5 3 Table 5 3 Word Length S...

Page 37: ...he INS8250 back to the inputs to allow the chip to be tested by writing data to itself and reading it back for verification This bit is ignored by the GPIB COM circuitry 3r w OUT2 Auxiliary Output 2 Bit The OUT2 serial port output is the inverse of this bit All interrupts from the serial adapter are disabled when this bit is cleared When this bit is cleared interrupts are disabled on the GPIB COM ...

Page 38: ...er Manual Bit Mnemonic Description 0r w DTR Data Terminal Ready Bit The DTR serial port output is the inverse of this bit This bit is set when the Controller is ready to communicate On the GPIB COM this bit is used along with the RTS bit to control the CTS bit of the Modem Status Register ...

Page 39: ...t is cleared when a character is transferred from the Transmitter Holding Register to the Transmitter Shift Register and set when the character has been shifted out of the Shift Register onto the serial output line On the GPIB COM there is no shift register so this bit behaves exactly the same as the THRE bit 5r THRE Transmitter Holding Register Empty Bit This bit is cleared when the processor wri...

Page 40: ...s asserted When the special function selection DIP switch has been set to disable the SRQ feature this bit is always clear 1r OE Overrun Error Bit This bit is set when a new character is received and stored in the Receive Buffer Register before the processor reads the previous character thus overwriting and destroying the previous character It is cleared when the processor reads the Line Status Re...

Page 41: ...ects the inverse of the serial port DCD input signal On the GPIB COM this bit is always clear 6r RI Ring Indicator Bit This bit reflects the inverse of the serial port RI input signal On the GPIB COM this bit is always clear 5r DSR Data Set Ready Bit This bit reflects the inverse of the serial port DSR input signal On the GPIB COM this bit is always set to indicate that the interface is ready to t...

Page 42: ...em Status Register On the GPIB COM this bit is always clear 1r DDSR Delta Set Ready Bit This bit is set when the serial port DSR input signal changes state and cleared when the processor reads the Modem Status Register On the GPIB COM this bit is always clear 0r DCTS Delta Clear to Send Bit This bit is set when the CTS input changes state and cleared when the processor reads the Modem Status Regis...

Page 43: ...ad to check if the Data Ready Bit is set When this bit becomes set the Receive Buffer Register is read to get the character that just came from the serial port and the process continues To transmit data the Line Status Register is polled until the Transmitter Holding Register Empty Bit is set A byte can then be written to the Transmitter Holding Register and polling continues Interrupt Driven Meth...

Page 44: ... on the GPIB COM sends the talk address that is set on the DIP switches addresses itself as a Listener and unasserts NRFD If the GPIB device sends a byte the GPIB COM accepts it stores it in the Receive Buffer Register and sets the DR bit of the Line Status Register At the end of the GPIB handshake it keeps NRFD asserted until the computer reads the byte from the Receive Buffer Register If the com...

Page 45: ...GPIB COM board Power Requirement 5 VDC 5 0 75 A typical Physical Dimensions 4 2 in by 8 75 in I O Connector IEEE 488 Standard 24 pin Operating Environment Component Temperature 0 to 70 C Relative Humidity 5 to 90 noncondensing Emissions FCC Class B Storage Environment Temperature 55 to 125 C Relative Humidity 5 to 90 noncondensing ...

Page 46: ... National Instruments Corporation B 1 GPIB COM User Manual Appendix B Multiline Interface Command Messages The following tables are multiline interface messages sent and received with ATN TRUE ...

Page 47: ...LA13 0E 016 14 SO 2E 056 46 MLA14 0F 017 15 SI 2F 057 47 MLA15 10 020 16 DLE 30 060 48 0 MLA16 11 021 17 DC1 LLO 31 061 49 1 MLA17 12 022 18 DC2 32 062 50 2 MLA18 13 023 19 DC3 33 063 51 3 MLA19 14 024 20 DC4 DCL 34 064 52 4 MLA20 15 025 21 NAK PPU 35 065 53 5 MLA21 16 026 22 SYN 36 066 54 6 MLA22 17 027 23 ETB 37 067 55 7 MLA23 18 030 24 CAN SPE 38 070 56 8 MLA24 19 031 25 EM SPD 39 071 57 9 MLA2...

Page 48: ...6D 155 109 m MSA13 PPE 4E 116 78 N MTA14 6E 156 110 n MSA14 PPE 4F 117 79 O MTA15 6F 157 111 o MSA15 PPE 50 120 80 P MTA16 70 160 112 p MSA16 PPD 51 121 81 Q MTA17 71 161 113 q MSA17 PPD 52 122 82 R MTA18 72 162 114 r MSA18 PPD 53 123 83 S MTA19 73 163 115 s MSA19 PPD 54 124 84 T MTA20 74 164 116 t MSA20 PPD 55 125 85 U MTA21 75 165 117 u MSA21 PPD 56 126 86 V MTA22 76 166 118 v MSA22 PPD 57 127 8...

Page 49: ...ssing and unaddressing devices and setting devices for remote or local programming Note The term command as used here should not be confused with some device instructions which are also called commands Such device specific instructions are actually data messages Talkers Listeners and Controllers There are three types of GPIB communicators A Talker sends data messages to one or more Listeners The C...

Page 50: ...hen the active or addressed Talker or Listener must be changed The Controller function is usually handled by a computer System Controller and Active Controller Although there can be multiple Controllers on the GPIB only one Controller at a time is Active Controller or Controller in Charge Active control can be passed from the current Active Controller to an idle Controller Only one device on the b...

Page 51: ... and most data use the 7 bit ASCII or ISO code set in which case the eighth bit DIO8 is unused or used for parity Handshake Lines Three lines asynchronously control the transfer of message bytes among devices The process is called a three wire interlocked handshake and it guarantees that message bytes on the data lines are sent and received without transmission error NRFD not ready for data NRFD i...

Page 52: ...tion across the interface ATN attention The Controller drives ATN true when it uses the data lines to send commands and false when it allows a Talker to send data messages IFC interface clear The System Controller drives the IFC line to initialize the bus to become Controller In Charge REN remote enable The System Controller drives the REN line which is used to place devices in remote or local pro...

Page 53: ... Devices are usually connected with a cable assembly consisting of a shielded 24 conductor cable with both a plug and receptacle at each end This design enables devices to be connected in either a linear or a star configuration or a combination of the two See Figures C 2 and C 3 Figure C 2 Linear Configuration of the GPIB Devices ...

Page 54: ...d connector is the Amphenol or Cinch Series 57 MICRORIBBON or AMP CHAMP type An adapter cable using non standard cable and or connector is used for special interconnect applications The GPIB uses negative logic with standard TTL logic levels When DAV is true for example it is a TTL low level 0 8 V and when DAV is false it is a TTL high level 2 0 V ...

Page 55: ...PIB is designed for the physical distance between devices and the number of devices on the bus is limited The following restrictions are typical A maximum separation of 4 m between any two devices and an average separation of 2 m over the entire bus A maximum total cable length of 20 m No more than 15 devices connected to each bus with at least two thirds powered on ...

Page 56: ...M User Manual Edition Date June 1990 Part Number 320197 01 Please comment on the completeness clarity and organization of the manual If you find errors in the manual please record the page numbers and describe the errors Thank you for your help Name Title Company Address Phone Mail to Technical Publications National Instruments Corporation 6504 Bridge Point Parkway MS 53 02 Austin TX 78730 5039 ...

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