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CHAPTER 2: Introduction
2. Introduction
2.1 Description
The IEEE 488 Bus Extenders and IEEE 488 Fiber Bus Extenders help you control
IEEE 488 devices up to 4000 feet (1219.2 m) from the host computer. This
overcomes the IEEE 488’s specified limit of 6 feet (1.8 m) between any two
devices, with a maximum of 60 feet (18.3 m) total chained length. In addition,
the Extenders allow up to 30 devices to be on the bus—double the 15-device limit
imposed by the IEEE standard.
You’ll need two Extenders for bus extension. The bus connecting the host
computer, or controller, is the “local” bus. The bus to which control is extended
is the “remote” bus. An Extender is required on each bus for IEEE bus extension.
The
IEEE 488 Bus Extender
(IC095A) transmits RS-422 data between Extenders.
RS-422, a differential serial data format, provides high noise immunity and long
distances using low-cost twisted-pair wire.
The
IEEE 488 Fiber Bus Extender
(IC096A) communicates serially over duplex
fiberoptic cables. Fiberoptic transmission provides even better noise immunity, low
RFI emissions, and long distances.
Extender operation is completely transparent to the system. The controller can
access both local and remote devices just as it could without the Extender, with the
exception of Parallel Poll (see “Parallel Poll Response Times” in
Chapter 4
).
