User`s manual

CHAPTER 9

BUS TUTORIAL

Operationally, the interface is thoughtfully supported with professional software

support package. The software provides high level language extensions that support

IEEE-488 bus data and i command transmission and reception. The function mnemon-

ics are identical to those found in the IEEE-488 standard. These mnemonics are used

by most manufacturers of IEEE-488 compatible equip ment.

To solve your interface problems you need a standard that goes beyond hardware and

software to provide consistency between different equipment manufacturers. The

world’s largest manufacturers of instrumentation, computers, and computer peripher-

als have chosen the IEEE-488 bus as the means for transferring information between

dissimilar devices. This gives you the ability to attach a printer from one manufactur-

er, a plotter from another, and instruments from a third and know that the system will

work. When you compare this to the number of serial and parallel interface cards it

would take to support fifteen incompatible peripherals, the decision to use the IEEE-

488 bus becomes obvious.

The IEEE-488 bus is a carefully defined instrumentation interface which simplifies the

integration of instruments, peripherals and computers into systems. It minimizes

compatibility problems between devices and has sufficient flexibility to accommodate

future products. The bus has been formally accepted by the International Electrotech-

nical Commission (I.E.C.), as an international standard, and by the Institute of

Electrical and Electronic Engineers (I.E.E.E.) as an American standard.

The IEEE-488 bus employs a 16 line to interconnect up to 15 instruments. This bus is

normally the sole communication link between the interconnected units. Each

instrument in the bus is connected in parallel to the 16 lines of the bus. Eight of the

lines are used to transmit data and the remaining eight are used for communication

timing and control.

Data is transmitted on the eight data lines as a series of eightbit characters referred to

as “bytes”. Normally, a seven-bit ASCII (American Standard Code for Information

Interchange) code is used with the eighth bit available for a parity check, if desired.

Data is transferred by means of an interlocked “handshake” technique. This sequence

permits asynchronous communication over a wide range of data rates.

Communication between devices on the IEEE-488 bus employs the three basic

functional elements listed below. Every device on the bus must be able to perform at

least one of these functions:

1) LISTENER. A device capable of receiving data from other devices. Typical listeners

are printers, programmable power supplies, programmable signal generators and the

like.