Chapter 3
Operation of the GPIB-232CV-A
3-4
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Choosing a Serial Port Buffer Size
All data that is sent to the GPIB-232CV-A is buffered and then passed
along to the destination port. Thus, any serial data received is buffered and
then passed along to the GPIB port whenever the GPIB-232CV-A is
addressed to talk. The GPIB-232CV-A has 256 KB of RAM for buffering.
In D mode, this memory can be allocated between the serial and GPIB
buffers in two possible configurations.
The size of the serial input buffer can be set to either 256 bytes
(SW1 switch 7 set to OFF), or 32 KB (SW1 switch 7 set to ON) with the
remainder of the 256 KB of RAM allocated to the GPIB buffer.
•
Set the serial input buffer size to 256 bytes if only small amounts of
data, such as status information from a plotter, are expected to be sent
from the serial device to the GPIB-232CV-A.
•
Set the serial input buffer size to 32 KB if you expect the serial device
to send large amounts of data to the GPIB-232CV-A, such as an
RS-232 instrument sending thousands of bytes of measurements.
In either case, the remainder of RAM space is used as the GPIB input
buffer. Thus, if a large amount of GPIB data is expected to be sent to the
GPIB-232CV-A, it would be advantageous to use the small 256 byte serial
port buffer size if possible. Then the majority of RAM is used as the GPIB
buffer. The larger serial buffer size is a means of capturing a larger
percentage of the total RAM space for serial input use.
Regardless of the buffer size you choose, serial data is not lost because the
GPIB-232CV-A implements a hardware handshake scheme, and if
selected, the XON/XOFF software handshake scheme. The variable buffer
size is a means of optimizing the GPIB-232CV-A for your application.
Using the SRQ Feature
The GPIB bus performance might slow down if the Controller is constantly
waiting for the GPIB-232CV-A to send or receive data. With SRQ enabled,
the bus can be used by other devices until the GPIB-232CV-A requests
service (asserts SRQ*). When the GPIB-232CV-A asserts SRQ*, the
Controller serial polls the GPIB-232CV-A to determine what type of
service it needs. After it is serial polled, the GPIB-232CV-A unasserts
SRQ*. You can enable the SRQ feature by setting switch 6 of SW1 to the
ON position.
