7.
The Listener unasserts NDAC. HS488-capable Listeners do not assert NRFD as IEEE
488.1 devices would, so the Talker determines that the addressed Listener is HS488-
capable.
8.
The Talker unasserts DAV and drives the next data byte on the GPIB.
9.
After allowing some settling time, the Talker asserts DAV.
10. The Listener latches the byte in response to the assertion (falling) edge of DAV.
11. After allowing some hold time, the Talker unasserts DAV and drives the next data byte on
the DIO signal lines.
Steps 9-11 are repeated for each data byte.
Case 2: Talker Is HS488-Capable, But Listener Is Not HS488-Capable
The following figure and procedure describe a typical sequence of events in an HS488 data
transfer in which the Talker is HS488-capable, but the Listener is not.
Figure 18. HS488-Capable Talker
Low-going transition on ~NRFD
indicates that not all receiving
devices are high-speed capable.
High-speed capable signal
~ATN
~DIO18
(composite)
~DAV
~NFRD
~NDAC
T1
Steps 1–6 in the sequence are identical to steps 1–6 in the previous procedure
and Listener are HS488 Capable
on page 23. The Listener ignores the HSC message from the
Talker.
Then, the IEEE 488.1 Listener enters ACDS and asserts NRFD. As a result, the Talker
determines that the addressed Listener is not HS488-capable. The Talker sources bytes using
the IEEE 488.1 protocol.
Case 3: Talker Is Not HS488-Capable, But Listener Is HS488-Capable
The Talker does
not
send an HSC message to the Listener, but sources bytes using the IEEE
488.1 protocol.
The addressed Listener (HS488 or IEEE 488.1) accepts bytes using the IEEE 488.1 standard
three-wire handshake, as shown in the following figure.
24
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GPIB-140B User Manual
