GPIB / IEEE488 Bus Description, HPIB Electrical Interface and IEEE-488 pinout. GPIB Information

GPIB Bus

General Purpose Interface Bus
IEEE-488 Digital Interface for Programmable Instrumentation

[GPIB Description]
[GPIB Data Transfer Timing] [IEEE488 Interface ICs]
[HPIB Connector] [IEEE488 PinOut] [GPIB Cable Assemblies] [IEEE488 Standards] [GPIB Software]
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GPIB Description [IEEE488]

GPIB Interconnect Modules, Instrument Control Modules

GPIB System

The IEEE-488 interface bus, also known as the General Purpose Interface Bus "GPIB" is an 8 bit wide byte serial, bit parallel interface system which incorporates: 5 control lines 3 handshake lines 8 bi-directional data lines. The entire bus consists of 24 lines, with the remaining lines occupied by ground wires. Additional features include: TTL logic levels (negative true logic), the ability to communicate in a number of different language formats, and no minimum operational transfer limit. The maximum data transfer rate is determined by a number of factors, but is assumed to be 1Mb/s. Devices exist on the bus in any one of 3 general forms: 1. Controller 2. Talker 3. Listener A single device may incorporate all three options, although only one option may be active at a time. The Controller makes the determination as to which device becomes active on the bus. The GPIB can handle only 1 ‘active’ controller on the bus, although it may pass operation to another controller. Any number of active listeners can exist on the bus with an active talker as long as no more then 15 devices are connected to the bus. The controller determines which devices become active by sending interface messages over the bus to a particular instrument. Each individual device is associated with a 5 bit BCD code which is unique to that device. By using this code, the controller can coordinate the activities on the bus and the individual devices can be made to talk, listen (un-talk, un-listen) as determined by the controller. A controller can only select a particular function of a device, if that function is incorporated within the device; for example a ‘listen’ only device can not be made to talk to the controller. The Talker sends data to other devices. The Listener receives the information from the Talker. In addition to the 3 basic functions of the controller, talker, and listener the system also incorporates a number of operational features, such as; serial poll, parallel poll, secondary talk and listen addresses, remote/local capability, and a device clear (trigger). Device dependent messages are moved over the GPIB in conjunction with the data byte transfer control lines. These three lines (DAV, NRFD, and NDAC) are used to form a three wire ‘interlocking’ handshake which controls the passage of data. The active talker would control the ‘DAV’ line (Data Valid) and the listener(s) would control the ‘NRFD’ (Not Ready For Data), and the ‘NDAC’ (Not Data Accepted) line. In the steady state mode the talker will hold ‘DAV’ high (no data available) while the listener would hold ‘NRFD’ high (ready for data) and ‘NDAC’ low (no data accepted. After the talker placed data on the bus it would then take ‘DAV’ low (data valid). The listener(s) would then send ‘NRFD’ low and send ‘NDAC’ high (data accepted). Before the talker lifts the data off the bus, ‘DAV’ will be taken high signifying that data is no longer valid. If the ‘ATN’ line (attention) is high while this process occurs the information is considered data ( a device dependent message), but with the "ATN’ line low the information is regarded as an interface message; such as listen, talk, un-listen or un-talk. The other five lines on the bus (‘ATN’ included) are the bus management lines. These lines enable the controller and other devices on the bus to enable, interrupt, flag, and halt the operation of the bus. All lines in the GPIB are tri-state except for ‘SQR’, ‘NRFD’, and ‘NDAC’ which are open-collector. The standard bus termination is a 3K resistor connected to 5 volts in series with a 6.2K resistor to ground - all values having a 5% tolerance. The standard also allows for identification of the devices on the bus. Each device should have a string of 1 or 2 letters placed some where on the body of the device (near or on the GPIB connector). These letters signify the capabilities of the device on the GPIB bus. C Controller T Talker L Listener AH Acceptor Handshake SH Source Handshake DC Device Clear DT Device Trigger RL Remote Local PP Parallel Poll TE Talker Extended LE Listener Extended Devices are connected together on the bus in a daisy chained fashion. Normally the GPIB connector (after being connected to the device with the male side) has an female interface so that another connector may be attached to it. This allows the devices to be daisy chained. Devices are connected together in either a Linear or Star fashion. Most devices operate either via front panel control or HPIB control (REMOTE). While using the front Panel the device is in the Local state, when receiving commands via the HPIB, the device is in the Remote state. The device is placed in the Remote state when ever the System Controller is reset or powered on,; also, when the system controller sends out an Abort message. In addition, if the device is addressed, it then enters the Remote state.

Extracted from 'GPIB Interface Design Document'. 6-13-86, Larry Davis

GPIB Connector Mechanical Dimensions

HPIB Connector Size, Mechanical Dimensions for HPIB Connector

GPIB Connector

IEEE-488 / ANSI Connector - Mechanical Drawing

Additional Military CID Mechanical Drawings, listed by CID number [Military Commercial Item Description].

{GPIB Index}

GPIB Bus Pin-Out Descriptions

IEEE-488 / ANSI Connector IEEE488 PinOut

**24-Pin GPIB Bus PinOut [IEEE488 Pinout]**
Pin #	Signal names	Signal Description	Pin #	Signal names	Signal Description
1	DIO1	Data Input/Output Bit 1	13	DIO5	Data Input/Output Bit 5
2	DIO2	Data Input/Output Bit 2	14	DIO6	Data Input/Output Bit 6
3	DIO3	Data Input/Output Bit 3	15	DIO7	Data Input/Output Bit 7
4	DIO4	Data Input/Output Bit 4	16	DIO8	Data Input/Output Bit 8
5	EIO	End-Or-Identify	17	REN	Remote Enable
6	DAV	Data Valid	18	Shield	Ground (DAV)
7	NRFD	Not Ready For Data	19	Shield	Ground (NRFD)
8	NDAC	Not Data Accepted	20	Shield	Ground (NDAC)
9	IFC	Interface Clear	21	Shield	Ground (IFC)
10	SRQ	Service Request	22	Shield	Ground (SRQ)
11	ATN	Attention	23	Shield	Ground (ATN)
12	Shield	Chassis Ground	24	Single GND	Single Ground

ATN: Attention; When low (true) the system places all devices in Command Mode, when high (false) the system places all devices in the Data Mode. In Command Mode the Controller passes data to devices, in Data Mode the Talker passes data to the Listener. All device must monitor the ATN line and respond within 200nS. EIO: End or Identify; Indicates the last data transfer of a multi-byte sequence or used by the system controller to indicate a Parallel Poll to a device (in conjunction with the ATN line). IFC: Interface Clear; Used only by the system controller to halt current operations. Placing all devices in an idle state. All talkers are set to Un-talk and all Listeners are set to Un-listen. Serial Poll is disabled. All devices shall monitor IFC, and respond within 100uS. REN: Remote Enable; Used by the system controller to place devices in programming mode. All Remote capable Listeners are set to remote operation ( if they were addressed to Listen), when REN is true (low). When low, devices are set to Local control. All device shall monitor the REN line, and respond within 100uS. SRQ: Service Request; Used by any device to indicate that a device needs service. Any device may use this line. Normally used as an interrupt line. The controller may masked this line, in favor of Polling. The SRQ line is cleared by a Serial Poll DIO1 to DIO8: Data Input-Output bus; Bi-directional, Bite Serial-Byte Parallel. Per data line, bits are serial, ASCII data is sent as parallel data. Standard data is 7 bit ASCII. But no coding format is defined with IEEE-488. NRFD: Not Ready For Data; Part of a three wire handshake. Used to indicate a device is ready for data, active low DAV: Data Valid; Part of a three wire handshake. Used to indicate valid data on the bus, active low NDAC: Not Data Accepted; Part of a three wire handshake. Used to indicate a device has not yet accepted data, active low

{GPIB Index}

GPIB On-Line Standards and Specifications Information

ANSI/IEEE 488.1 [IEC 60625-1] IEEE Standard Digital Interface for Programmable Instrumentation
Defines the Physical and Electrical layer, and signaling protocol.

ANSI/IEEE 488.2 IEEE Codes, Formats, Protocols, and Common Commands, and Standard Commands for Programmable Instruments

IEC/IEEE 60488-2 defines communication protocols for devices connected via IEEE 488 buses and common commands and characteristics useful in a wide range of instrument applications. It includes message-handling protocols, status reporting structures, and system configuration and synchronization protocols.

HS488 High-Speed GPIB Handshake Protocol Hand shake protocol, increases bus transfers to 8MBytes/s with other HS488 devices. NDAC is not required to Handshake, The Talker outputs data with DAV, waits then outputs new data with DAV without NDAC occurring.

SCPI Standard Commands for Programmable Instruments Defines a programming language for Instruments

{HPIB Bus Index}

IEEE488 Bus Interface IC Manufacturers

Standard TTL levels (2.0v/0.8v) @ 5.2mA source / 48mA sink, Totem Pole, Open Collector and Tristate devices are used with IEEE488.
Open Collector: SRQ, NRFD, NDAC
Open Collector or Tristate: ATN, IFC, REN, EOI, DAV.

MC3446; Quadruple Bus Transceiver [IEEE Standard 488 Compliant], 16-pin DIP [Obsolete part].
MC3447; Bidirectional Instrumentation Bus [GPIB] Transceiver, 24-pin DIP [Obsolete part].

ines-Innovative Electronic Systems {CMOS GPIB interface ASIC ICs}

National Instruments {HS-488 Controller TNT4882-Controller NAT9914A, Talker/Listener}

National Semiconductor {IEEE-488 GPIB Transceiver ICs 75160 / 75162}

TI {Controller TMS9914A-Transceiver, 75xx160/161/162}

There is not much special about driving over a IEEE488 bus, the original interface ICs were just normal TTL devices.
The Octal Transceiver 74F588 was used in many applications.

Federal stock class designator: [DOD Drawing numbers]
5962-89680; Microcircuit Linear, Octal General Interface Bus Transceiver [GPIB]
5962-89681; Microcircuit Linear, Octal General Interface Bus Transceiver [GPIB], Generic number 55ALS161

IC Manufacturers Listing All other device types

**IEEE-STD-488 I/O Characteristics**
Single Type	Digital Value
Input Voltage High:	V_IH = 3.4 volts typical, 2.4 volts minimum
Input Voltage Low:	V_IL = 0.22 volts typical, 0.4 volts maximum
Input Current High:	I_IH = 2.5mA maximum
Input Current Low:	V_IL = -3.2mA maximum
Output Voltage High:	V_OH = 3.4 volts typical, 2.5 volts minimum
Output Voltage Low:	V_OL = 0.22 volts typical, 0.5 volts maximum
Output Current High:	I_OH = -5.2mA maximum
Output Current Low:	I_OL = 48mA maximum

{GPIB Bus top}

IEEE488 Data Bus Transfer Timing

GPIB Bus Handshake Timing

The IEEE488 bus operates at the speed of the slowest device, all devices have to be ready before operation begins.
Signals are active low. Data is transferred asynchronous, using the Handshake lines instead of a clock.
Only Parallel Polling does not use the Handshake, all other transfers use Hand-shaking.

HS488 High-Speed GPIB Handshake Protocol Hand shake protocol [not shown above], increases bus transfers to 8MBytes/s with other HS488 devices.
NDAC is not required to Handshake, the Talker outputs data with DAV, waits then outputs new data with DAV without NDAC occurring.

{HPIB Index}

GPIB Cable Assemblies

GPIB Cable

Connector Type: (The connector pin-outs differ) ....
IEEE488/ANSI MC1.1; 24 pins, accepts a ribbon cable. ....
IEC 625-1, MIL-C-24308; 25 pins
Connectors are tested to MIL-STD-202E (Environmental).

IEEE488 has a Maximum cable length of 20 meters, or 2 meters per device - which ever is less.
IEEE488 devices may be connected in either a Star or Linear fashion [Device-to-Device].

GPIB Cable Manufacturers
Belden
Keithley {Single/Double shielded GPIB Cables, IEEE-488 to Centronics cable adapter}
INES Test and Measurement
Normal cable lengths; 0.5 meters, 1m, 2m, and 4 meters.

Metric threads are Black, English threads are Silver; the two will not mate together.

{IEEE488 Index}

GPIB Software

IEEE-728-1982 Recommended Practice for code and Format Conventions for IEEE Standard 488
IEC 625-2 ------
NOTE: The IEEE-488 is very easy to program, just send the device address, command, and function.
Example of HP BASIC used over IEEE-488 [programming example].

NOTE: The IEEE-488 is also know by a number of other names, which all mean the same thing.
GPI Bus; General Purpose Interface Bus
GPIB; General Purpose Interface Bus
HPIB; Hewlett-Packard Interface Bus
IEEE-488; Adopted by the Institute of Electrical and Electronic Engineers [US Standard]
IEC 60488; Adopted by the International Electrotechnical Commission [International Standard]
IEC 60625-1; Adopted by the International Electrotechnical Commission [International Standard], Old IEC version ?
Is there a difference between the US standards or names, NO; but there may be between the US and International Standard.
IEC 60625-2; No data
IEEE1174; may be an application of IEC 60625-2, which translates GPIB functionality to a serial RS232 line.

USB to GPIB translation; no defined standard.

Adlink Technology Inc. {IEEE-488 to USB GPIB Interface Controller Cable device}

Editor Note; The GPIB interface has been around for decades, my first design implementing a GPIB interface was back in 1986. However no matter how old the 488 interface is there are still thousands of fielded devices being used in industry which need to be accounted for. Many companies are not going to replace a device just because of its age, however a device would be replaced it it could no longer fulfill a function. Again power supplies, signal generators and many other types of lab equipment never really go obsolete [a BERT or Eye Scope sure will].

To be sure the IEEE488 interface is an old and dated method of commanding a piece of equipment. But again, if you only need to transfer an 8-bit command every few seconds the HPIB will continue to be found on lab gear; although not on all new gear. A quick check indicates that a high speed BERT does include a GPIB interface as an option. After all it is a cheap interface to add, and if it makes a sale.
The most common upgrade path is to use a USB to GPIB interface module. However much of the Programmable Instrumentation delivered over the last decade contained an Ethernet port instead of or in addition to the 488 bus.
The proper upgrade when buying new test equipment is to select an LXI bus [LAN eXtensions for Instrumentation], if one resides on the selected gear; otherwise there should be an Ethernet port.

So IEEE488 is a legacy interface, but easy to design a hardware interface to; but, even if you don't need communication speed, you my want processor speed ~ as the older HPIB may be claiming more processing power than a newer Ethernet interface. Than again, it all depends how the electrical portion of HPIB interacts with the cpu located in the device. By slowing down the processor, I'm referring to the cpu waiting on the slow transfer speed of the bus to finish talking to the interface.

All these comments only relate to tech labs that communicate to there devices over some interface. If you just use the front panel controls than none of this matters.

GPIB Search Trend

2004 to 2011 Search History

The graph shows the declining interest in the IEEE488 interface bus over the last five years. Although no inference can be gain about the future of the bus, the graph makes clear the point that fewer people are searching for information regarding the GPIB interface.

The argument could be made that engineers are still searching for GPIB data, but not using Google, which has 70 percent of the search market. Even that as a mature subject every company already own the IEEE488 standard and does not need to look up any data. However, the GPIB standard does not give any insight into designing with the standard or the pitfalls that might be encountered.

Should the GPIB interface bus continue to be used, that would depend on the number of pieces of equipment all ready owned or being used in a particular lab. Of course usage also depends on the amount of code already written. Even though writing code for the GPIB is relatively straightforward, coding for the Ethernet bus may not be [even requiring a new software package].

A comparison could be made with the LXI bus, but the search trend for that term is basically a straight line at unity between the dates covered in the graph above [showing no useful data].

The Recommendation is to replace the GPIB interface. The connector is 4 times the size of an RJ [Ethernet] connector, and the GPIB cable is at least three times as thick as a LAN cable. Of course any interface transfers data faster than the GPIB.

Topic Navigation: Engineering Home > Interface Buses > Cabled Interface Standards > HPIB Interface.

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