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Conditions That Cause SRQ to be Asserted
If SRQ is enabled, the GPIB-232CV-A asserts the SRQ* signal on two
conditions:
•
When the GPIB-232CV-A receives serial data that it needs to pass on
to the GPIB port
•
When the GPIB input buffer becomes empty
When the GPIB-232CV-A serial input buffer is empty and the
GPIB-232CV-A receives a serial character to be sent along to the GPIB, the
SRQ* signal is asserted. This alerts the GPIB Controller that the
GPIB-232CV-A has data to send to a GPIB Listener. The Controller can
then address the GPIB-232CV-A to talk so that the data can be read out of
the GPIB-232CV-A serial buffer. When the serial buffer is empty, the
Controller can unaddress the GPIB-232CV-A to talk and address other
devices to transfer data on the bus.
SRQ* is also asserted when the GPIB input buffer becomes empty. When
the GPIB-232CV-A has emptied out the buffer, it requests service,
indicating it is ready for more data. The Controller can then readdress the
GPIB-232CV-A to listen and continue sending data until all the data is sent.
Maximizing Performance with SRQ
If large amounts of data (greater than the GPIB buffer size) are sent over
the GPIB to the GPIB-232CV-A and the serial device is a very slow data
acceptor, the GPIB-232CV-A internal GPIB data buffer might become full.
If this occurs, the FULL indicator on the front panel illuminates and the
GPIB transfer rate slows to approximately the same rate as the serial device
that is accepting the data. Because the maximum data transfer rate on the
GPIB is only as fast as the slowest Listener, the GPIB system performance
may become unacceptable if other GPIB devices are required to transfer
data on the bus.
To get maximum GPIB performance when large amounts of data are sent
to the GPIB-232CV-A, enable the SRQ feature and send only data amounts
up to but not exceeding the GPIB input buffer size. The Controller can then
unaddress the GPIB-232CV-A to listen so that other devices can use the
bus. When the GPIB-232CV-A is ready to receive more data, it asserts the
SRQ* signal.
Chapter 3
3-5
Operation of the GPIB-232CV-A
GPIB-232CV-A User Manual
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