Introduction to HS488
Appendix C
GPIB-140 User Manual
C- 4
© National Instruments Corp.
Case 1: Talker and Listener Are
HS488 Capable
The following steps describe a typical sequence of events in an HS488 data transfer in
which the Talker and Listener are both HS488 capable. Refer to Figure C-2.
~ATN
~DIO1-8
(composite)
~DAV
~NDAC
2nd byte transferred
(using high-speed mode).
Lack of low-going transition on
~NRFD indicates that all receiving
devices are high-speed capable.
The sending device uses this "high
speed capable" signal (the momentary,
low-going pulse on ~NRFD) to tell the
receiving device that the sending
device is capable of sending data using
the high-speed handshake.
1st byte transferred
(using 488.1 handshake).
T13 T14
~NRFD
T1
Figure C-2. Talker and Listener Are HS488 Capable
1.
The Controller addresses devices and becomes Standby Controller by unasserting
ATN.
2.
The Listener asserts NDAC and NRFD.
3.
The Listener unasserts NRFD as it becomes ready to accept a byte.
4.
After allowing time for the Listener to detect NRFD unasserted, the Talker indicates
that it is capable of HS488 operation by sending the HSC message. To send the
HSC message true, the Talker asserts the NRFD signal.
5.
After allowing time for the Listener to respond to the HSC message, the Talker
sends the HSC message false. To send the HSC message false, the Talker unasserts
the NRFD signal.
6.
When the Talker has a byte ready to send, it drives the data on the DIO signal lines,
allows some settling time, and asserts DAV.
