APS APS-3000P Series - Page 72

CHAPTER 5
APPLICATIONS
Entire Contents Copyright  2004 by Adaptive Power Systems, Inc. (APSI) • All Rights Reserved • No reproduction without written authorization from APSI.
APS-3000P Series 5 - 13 OM-001-03000-00P-03.9
GPIB Handshake Lines
Three GPIB lines asynchronously control the transfer of message bytes between
devices. Called the 3-wire interlocked handshake, this protocol guarantees that
message bytes on the data lines are sent and received without transmission error.
 NRFD (not ready for data) - Indicates when a device is ready or not ready to receive
a message byte. The line is driven by all devices when receiving commands, by
Listeners when receiving data messages, and by the Talker when enabling the
HS488 protocol.
 NDAC (not data accepted) - 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) - 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 DAV when sending data messages.
GPIB Interface Management Lines
Five lines 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 drives ATN false when a Talker can send data messages.
 IFC (interface clear) - The System Controller drives the IFC line to initialize the
bus and become CIC.
 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.
 EOI (end or identify) - The EOI line has two purposes: (1) The Talker uses the EOI
line to mark the end of a message string, and (2) the Controller uses the EOI line
to tell devices to identify their response in a parallel poll.
GPIB Connectors and Cables
Additional connector and cable diagrams are not provided for GPIB. APS assumes you
are using high-quality commercial cables and connectors that are essential for
obtaining high-speed performance provided by the GPIB bus.