
Section 3 IEEE 488 Primer
3.6
waits until
NRFD
is unasserted (high) which indicates that all Addressed
Listeners are ready to accept the information. When
NRFD
and
NDAC
are in
the proper state, the
Talker
asserts
DAV
( active low) to indicate that the data
on the bus is valid.
3.5.2 Not Ready for Data (NRFD)
This line is used by the
Listeners
to inform the
Talker
when they
are ready to accept new data. The
Talker
must wait for each
Listener
to
unassert this line (high) which they will do at their own rate when they are ready
for more data. This assures that all devices that are to accept the information are
ready to receive it.
3.5.3 Not Data Accepted (NDAC)
The
NDAC
line is also controlled by the
Listeners
. This line
indicates to the
Talker
that each device addressed to listen has accepted the
information. Each device releases
NDAC
(high) at its own rate, but the
NDAC
will not go high until the slowest Listener has accepted the data byte.
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