National Instruments GPIB-422CV, Руководство пользователя

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Chapter 3 Operation
© National Instruments Corp. 3-3 GPIB-232CV User Manual
will not be lost regardless of the serial buffer size you choose. The larger
serial buffer size is simply provided as a means of capturing a larger
percentage of the total RAM space for serial-input use. For example, if you
were connecting an RS-232 device capable only of transmitting data to the
GPIB-232CV, you would definitely want to use the 32 KB serial buffer to
maximize the use of the available RAM space.
Using the SRQ Feature
If your GPIB system has GPIB devices other than the GPIB-232CV that
need to transfer data, and it is important that the GPIB bus not be slowed
down or hung waiting for the GPIB-232CV to either receive serial data to
be passed along to the GPIB or accept more GPIB data because its GPIB
input buffer is full, then the SRQ feature can be enabled. The SRQ feature
will alert the GPIB Controller by asserting the GPIB signal
SRQ* when the
GPIB-232CV requires attention. The Controller can then determine the
status of the GPIB-232CV by performing a serial poll and analyzing the
response byte. In this way, the GPIB bus can be used by other devices until
service is required by the GPIB-232CV.
To get maximum GPIB performance when very large amounts of data are
sent to the GPIB-232CV, enable the SRQ
feature and only send data
amounts up to but not exceeding the GPIB input buffer size. The Controller
can then unaddress the GPIB-232CV to listen and allow other devices to
use the GPIB. When the GPIB-232CV has emptied out its GPIB input
buffer, it will request service, indicating it is ready for more data. The
Controller can then re-address the GPIB-232CV to listen and continue
sending data in the manner described until all the data has been sent.
Enabling the SRQ Feature
The SRQ feature can be enabled by setting switch 3 of the configuration
switch at location U22 to the ON position. When enabled, the
GPIB-232CV will assert the
SRQ* signal whenever either the GPIB input
buffer becomes empty or the GPIB-232CV receives serial data that it needs
to pass on to the GPIB port.
SRQ* will be unasserted when the GPIB
Controller performs a serial poll on the GPIB-232CV.