Operation of the GPIB
Appendix C
GPIB-SCSI-A User Manual
C-4
© National Instruments Corp.
NDAC* (not data accepted)
NDAC* indicates when a device has or has not accepted a message byte.
The line is driven by all devices when receiving commands and by Listeners
when receiving data messages.
DAV* (data valid)
DAV* tells when the signals on the data lines are stable (valid) and can be
accepted safely by devices. The Controller drives DAV* when sending
commands and the Talker drives it when sending data messages.
Interface Management Lines
Five lines are used to manage the flow of information across the interface.
ATN* (attention)
The Controller drives ATN* true when it uses the data lines to send
commands and false when it allows a Talker to send data messages.
IFC* (interface clear)
The System Controller drives the IFC* line to initialize the bus and become
Controller-In-Charge.
REN* (remote enable)
The System Controller drives the REN* line, which is used to place devices
in remote or local program mode.
SRQ* (service request)
Any device can drive the SRQ* line to asynchronously request service from
the Controller.
