Appendix A
GPIB Basics
GPIB-120B User Manual
A-6
ni.com
Figure A-2.
Linear and Star System Configuration
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.
Device A
Device B
Device C
Device D
Device A
Device C
Device B
a. Linear Configuration
b. Star Configuration
