Chapter 1
Introduction
© National Instruments Corp.
1-3
GPIB-140 User Manual
The GPIB-140 and GPIB-140/2 bus extenders comply with the specifications of the
ANSI/IEEE Standard 488.1 -1987 and the ANSI/IEEE Standard 488.2-1992, including the
Find Listeners protocol. With the GPIB extenders, you can overcome the following two
configuration restrictions imposed by ANSI/IEEE Standard 488.1-1987:
•
A cable length limit of 20 m total per contiguous bus or 2 m times the number of
devices on the bus, whichever is smaller.
•
An electrical loading limit of 15 devices per contiguous bus.
Each GPIB-140 system extends the GPIB to a maximum distance of 1 km, and each
GPIB-140/2 system extends the GPIB to a maximum distance of 2 km. Both types of
systems extend the loading limit to 28 devices (including the GPIB extenders), without
sacrificing speed or performance. These point -to-point extension systems can be
connected in series for longer distances or in star patterns for additional loading.
The maximum data transfer rate over the extension is 2.2 Mbytes/s using HS488
protocol. The GPIB extender uses a buffered transfer technique with a serial extension
bus to get maximum performance while keeping the cabling cost at a minimum.
Furthermore, there is no speed degradation for transfers between devices on the same side
of the extension. The GPIB extender also has error-checking capabilities to ensure
successful data transmission over the fiber optic link.
Because the GPIB-140 and the GPIB-140/2 are functionally transparent extenders, the
same GPIB communications and control programs that work with an unextended system
can work with an extended system. The Parallel Poll Response (PPR) Modes section of
Chapter 3, Configuration and Operation , discusses one minor exception to this
transparency in conducting parallel polls .
