IEEE-488 the Intrepid Interface

May 24, 2018 at 8:00 AM

 

Developed by Hewlett Packard in the 1960s, IEEE-488 was designed to easily interconnect controllers and instruments.  Originally named HP-IB (Hewlett Packard Interface Bus), and now largely known as GPIB (general purpose interface bus), the interface was adopted and renamed by various institutions and standards bodies including the IEEE, which named it IEEE-488. No matter what you call it, this die-hard interface has endured throughout the years and is still widely used.  

 

The basic concept of IEEE-488 is an extremely flexible system that allows data to be transmitted between any instrument on the bus. It has a 24-pin connector and is double-headed, both ends of the cable are used, with female on one end and male on the other. There are 16 signal lines, eight for bi-directional communication, five for bus management and three lines are used for handshakes.

 

The speed of the data flow is determined by the slowest active instrument and the max data rate is around 1 Mbps. As many as 15 instruments can be connected on a bus with a maximum total length of 20 meters and no more than 2 meters between two adjacent instruments. Active extenders can be used to create longer buses that can connect up to 31 devices.

 

The way the IEEE-488 operates is that each instrument on the bus has a unique address and no two instruments can have the same address. The connected equipment is allocated into three categories, with some items serving more than one function (i.e. listener/talker):

 

  • · Controller – The controller is in charge of controlling the operation of the bus. This device, usually a computer, instructs the other instruments to perform in their various roles. The controller also makes sure that there aren’t any conflicts on the bus. For example, if two talkers talk at the same time, data would be corrupted and the system operation would be compromised. Several controllers can share the same bus, but only be one can be active at a time.

 

  • · Listener – A listener is connected to and accepts instructions from the bus. One example would be a printer that only accepts information.

 

  • · Talker – A talker returns data and instructions to the bus. For example, a meter being used on the bus would be a talker when it’s providing data.

 

Today, IEEE-488 is the most common communication interface for scientific and engineering instruments, it is also used in a wide range of applications including data acquisition. Most bench instruments accept IEEE-488 as a standard fitting or as an option to make it easy to use test equipment in various applications, aside from only being used in an ATE test stack. Though the interface is not standard on today’s computers, a GPIB card can be easily installed. Because of its flexibility and convenience, IEEE-488 and is still widely used today and will likely remain relevant for years to come.

 

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