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A-5
GPIB-120B User Manual
The standard connector is the Amphenol or Cinch Series 57
Microribbon
or
Amp Champ
type.
For special interconnection applications, use an adapter cable using a non-standard cable and/or
connector.
The GPIB uses negative logic with standard TTL (transistor-transistor logic) level. For example,
when DAV is true, it is a TTL low level (
0.8 V), and when DAV is false, it is a TTL high level
(
2.0 V).
Configuration Requirements
To achieve the high data transfer rate that the GPIB was designed for, you must limit the number
of devices on the bus and the physical distance between devices. The following restrictions are
typical:
•
A maximum separation of 4 m between any two devices and an average separation of 2 m
over the entire bus.
•
A maximum total cable length of 20 m.
•
A maximum of 15 devices connected to each bus, with at least two-thirds powered on.
For high-speed operation, the following restrictions apply:
•
All devices in the system must be powered on.
•
Cable lengths must be as short as possible with up to a maximum of 15 m of cable for each
system.
•
There must be at least one equivalent device load per meter of cable.
To exceed these limitations, you can use a bus expander to increase the number of device loads.
You can order GPIB-120B bus expanders from National Instruments.
