GPIB Cables Connectors and Pin-outs

- information and data for IEEE 488 or GPIB cables, GPIB connectors and the GPIB pin outs or pin allocations used for GPIB inter-connections.

This GPIB tutorial is split into several pages each of which address different aspects of GPIB operation and technology:

The GPIB / IEEE 488 interface is well established in the electronics industry as a means of providing control of remote test and measurement instruments. Although the GPIB interface has been in widespread use since the early 1970s, the use of the GPIB interface continues in view of its convenience and availability The GPIB cables and GPIB connectors are in widespread use and are available from many stockists and suppliers.

While GPIB connectors and GPIB cables are widely available and can be used with little knowledge, some background information can be useful.

GPIB connector

The connector used for the IEEE 488 bus is standardised as a 24-way Amphenol 57 series type. This provides an ideal physical interface for the standard. The IEEE 488 or GPIB connector is very similar in format to those that were used for parallel printer ports on PCs. This makes the GPIB connector a sufficiently rugged connector for use in a variety of test equipment and test and measurement environments where unprotected connectors may not survive well.

An additional advantage of the GPIB connector is that it has a screw-lock. In this way, once the connectors have been mated the screw-lock can be used to secure the connectors together. In this way movements of the GPIB cables are unlikely to cause any intermittent connections. With complicated electronics systems such as automatic test systems, intermittent cable connections can cause significant problems which can be difficult to isolate and cure. By using a GPIB connector that has a screw-lock this problem can be overcome.

The basic female connector used on the GPIB equipments follows the standard format for the Amphenol 57 series, the GPIB cable connector has some differences. The basic GPIB cable connector has a male to female capability. In this several GPIB cables connectors can be "piggy-backed" on top of each other. This helps the physical setting up of the bus and prevents complications with special connection boxes or star points, etc.

There are two different types of screwlock used on the GPIB connectors. The metric threads are Black whereas English threads are Silver. Unfortunately the two will not mate together. The most common type of screwlock is the black metric version.

GPIB cables

In practice the GPIB interface is very easy to use. Ready-made GPIB cables are widely available even if they appear to be a little expensive. However these GPIB cables are fully screened and have the correct lines as twisted pairs. This considerably reduces the susceptibility of the bus to data corruptions. Manufacture of full specification GPIB cables can be difficult in view of the complexity of the cable and having to ensure the integrity of the screening.

A cheap and convenient alternative for GPIB cables is available in the form of insulation displacement connectors. While cables made in this way are much cheaper they are not screened and do not conform to the GPIB / IEEE 488 specifications. In view of this they should only be used where there are a very limited number of instruments, where data rates are likely to be low, for long runs, and where electrical noise is not likely to be a problem. If a cable of this nature is used then it is worth being aware that it could be the cause of random errors when the system is operating.

Although there is a considerable degree of flexibility when setting up a GPIB system, there are some restrictions on the way the GPIB cables are set up. Up to fifteen instruments may be connected together with a maximum bus length not exceeding 20 metres. There must also be no more than 2 metres between any two instruments. Devices on the GPIB can be connected in either a star or linear configuration.

Although a variety of GPIB cable products are available, typically they are available in set lengths. The most common lengths for GPIB cables are: 1 metre and 2 metres. Longer GPIB cables are not normally available in view of the GPIB overall bus restrictions. Some 0.5 metre GPIB cables are available, but these are often too short for many applications in view of the lack of cable flexibility.

Although GPIB cables are normally quite reliable, their construction means that they are not easy to flex. As a result, GPIB cables seem to have a limited life and as a result, care should be taken when re-using old GPIB cables.

GPIB pin-outs

The connections or pinouts for the GPIB connector are given in the table below:

Summary

GPIB is widely used for test instrumentation and data acquisition. Despite the fact that it has been in use for many years, the GPIB standard offers flexibility and convenience, allowing stand-alone bench test equipment to be sued in an automated fashion. Accordingly many GPIB cables and GPIB connectors are required and these are also in plentiful supply. It is also useful to have a table of the GPIB pinouts for occasions when individual connections may be required.

Further pages from this tutorial
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