Operation
Chapter 3
GPIB-232CV User Manual
3-4
© National Instruments Corp.
Conditions that Assert SRQ
When the SRQ feature is enabled, one of the conditions that causes a
service request is when the GPIB-232CV serial input buffer is empty.
Then, the GPIB-232CV receives a serial character to be sent along to the
GPIB. The SRQ* signal is asserted to alert the GPIB Controller that the
GPIB-232CV has data to send to a GPIB Listener. The GPIB-232CV can
then be addressed to talk so that the data can be read out of the
GPIB-232CV serial buffer. After all data has been read, the Controller can
unaddress the GPIB-232CV to talk so that other devices can be addressed to
transfer data on the bus.
The other condition on which SRQ* will be asserted, if enabled, is when
the GPIB input buffer becomes empty. If very large amounts of data are
sent over the GPIB to the GPIB-232CV (greater than the GPIB buffer size)
and the serial device is a very slow data acceptor, the GPIB-232CV internal
GPIB data buffer might become full. If this does occur, the FULL
indicator on the front panel will illuminate and the GPIB transfer rate will
slow to approximately the same rate as the serial device accepting the data.
Since 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 need to transfer data on the bus.
Serial Poll Responses
If the GPIB-232CV is serial polled, its response byte will depend upon the
status of the internal data buffers. If the serial input buffer is empty, bit one
of the status byte will be set to 1. If the serial input buffer is not empty, bit
one will be set to 0. If the GPIB input buffer is empty, bit zero of the status
byte will be set to 1. If the GPIB input buffer is not empty, bit one will be
set to 0. In all cases, bit six will be set to 1 if the GPIB-232CV is
requesting service, and will be set to 0 otherwise.
Listen-Only Mode
The GPIB-232CV will be located at the GPIB address specified by switches
4 through 8 of the configuration DIP switch at location U22. The
GPIB-232CV also has the ability to be configured as a listen-only device if
all GPIB address switches are set to ON. In the listen-only mode, no
addressing is required to make the GPIB-232CV a GPIB Listener and it
cannot be unaddressed to listen. All data transferred on the GPIB will be
accepted by the GPIB-232CV and output to the serial port (even if the data
Summary of Contents for GPIB-232CV
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