Black Box IC026AE-R2, IC026A-R2 manual Ieee 488 Primer, History, General Structure

CHAPTER 6: IEEE 488 Primer

6. IEEE 488 Primer

6.1 History

The IEEE 488 bus is an instrumentation-communication bus adopted by the Institute of Electrical and Electronic Engineers in 1975 and revised in 1978. The interface converter conforms to this most recent revision, designated IEEE 488-1978.

Before this standard was adopted most instrumentation manufacturers offered their own versions of computer interfaces. This placed the burden of system hardware design on the end user. If your application required the products of several different manufacturers, then you might need to design several different hardware and software interfaces.

The popularity of the IEEE 488 interface (sometimes called the General Purpose Interface Bus or GPIB) is due to the total specification of the electrical and mechanical interface as well as the data transfer and control protocols. The use of the IEEE 488 standard has moved the responsibility of the user from design of the interface to design of the high-level software that is specific to the measurement application.

6.2 General Structure

The main purpose of the GPIB is to transfer information between two or more devices. A device can either be an instrument or a computer. Before any information transfer can take place, it is first necessary to specify which will do the talking (send data) and which devices will be allowed to listen (receive data). The decision of who will talk and who will listen usually falls on the System Controller, which is the Active Controller at power-on.

The System Controller is similar to a committee chairman. On a well-run committee, only one person may speak at a time and the chairman is responsible for recognizing members and allowing them to have their say. On the bus, the device that is recognized to speak is the Active Talker. There can only be one Talker at a time if the information transferred is to be clearly understood by all. The act of “giving the floor” to that device is called Addressing to Talk. If the committee chairman cannot attend the meeting, or if other matters require his attention, he can appoint an acting chairman to take control of the proceedings. For the GPIB, this device becomes the Active Controller.

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