National Instruments GPIB-SCSI-A, Руководство пользователя

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Appendix C Operation of the GPIB
© National Instruments Corp. C-5 GPIB-SCSI-A User Manual
EOI* (end or identify)
The EOI* line has two purposes. The Talker uses the EOI* line to mark the
end of a message string. The Controller uses the EOI* line to tell devices to
identify their response in a parallel poll.
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. This design allows devices to be linked in either a linear or a star
configuration, or a combination of the two. See Figures C-1, C-2, and C-3.
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 interconnection 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).