Measurement Computing Extender488 - Manual (Page 5)

Section 1 Introduction
1-1
INTRODUCTION
1.1 DESCRIPTION
The Extender488s enable IEEE 488 devices to be co ntrolled up to 4,000 feet from the h ost
computer. This overcomes the limit imp osed by t he IEEE 488 specification of 6 feet between any two
devices, to a m aximum of 60 feet total chained length. I n addition, the Extender488s allows up to 30
devices to be on the bus, versus the 15 device limit imposed by the IEEE standard.
Two extenders are required to perform bus extension. The bus connecting the host computer, or
controller, is the "local" bus. T he bus to which control is extended is the "remote" bus. One of the
Extender488s is required on each bus to accomplish IEEE bus extension.
Communication between extenders is accomplished with serial data transmission, using RS-422 data
drivers and receivers with the Extender488. This differential serial data format provides high noise
immunity and long-distance capability using low cost twisted pair wire.
The Extender488/F communicates serially over duplex fiber optic cables. Fiber optic transmission
provides high noise immunity, low RFI emissions and long-distance capability.
Operation of the Extender488s is completely transparent to the system. The controller can access
both local and remote devices in exactly the same manner, with the exception of Parallel Poll.