National Instruments GPIB-120A - Manual (Page 23)

Appendix A Operation of the GPIB
© National Instruments Corporation A-5 GPIB-120A User Manual
Physical and Electrical Characteristics
Devices are usually connected with a cable assembly consisting of a shielded 24 conductor cable
with both a plug and receptacle connector at each end. With this design, devices can be linked in
either a linear configuration (shown in Figure A-2) or a star configuration (shown in
Figure A-3), or a combination of the two.
The standard connector is the Amphenol or Cinch Series 57 Microribbon or Amp Champ type.
An adapter cable using a non-standard cable and/or connector is used for special interconnecting
applications.
The GPIB uses negative logic with standard TTL logic levels. When DAV is true, for example,
it is a TTL low level (
≤
0.8 V), and when DAV is false, it is a TTL high level (
≥
2.0 V).
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24 DIO5
DIO6
DIO7
DIO8
REN
GND (TW PAIR W/DAV)
GND (TW PAIR W/NRFD)
GND (TW PAIR W/NDAC)
GND (TW PAIR W/IFC)
GND (TW PAIR W/SRQ)
GND (TW PAIR W/ATN)
SIGNAL GROUND
DIO1
DIO2
DIO3
DIO4
EOI
DAV
NRFD
NDAC
IFC
SRQ
ATN
SHIELD
Figure A-1. GPIB Connector and the Signal Assignment