Reply Output Buffer - Racal Instruments 1256 Manual

1256 User Manual

Reply Output Buffer

SCPI Command Basics 5-26
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bottom line. The default power-up state of the instrument is no flow
control. To select a different power-up state, this setting like all
other menu options can be saved to non-volatile memory. For
further details on front-panel usage refer to Chapter 3: USING
THE FRONT PANEL CONTROLS.
The 1256 waits for a linefeed (carriage return or carriage
return/line feed will also work in RS-232 mode if the 1256 is
configured properly) or GPIB EOI terminator before any command
is parsed. If 1024 characters are sent to the 1256 without any
terminators, the 1256 will flush both input and output buffers and
then queue and error message.
Because the 1256 uses an input buffer to store commands, it is
possible that multiple CLOSE or OPEN commands may be stored
in the input buffer before the first command is executed. To
synchronize the application program with the 1256, and to ensure
that relays are in the programmed state, a query may be sent to
the 1256. Once the reply to the query is read, you can be sure that
the relays are in the programmed state.
For example, the following command sequence may be used:
CLOSE (@5(0))
OPEN (@5(12))
CLOSE (@5(17))
OPEN (@5(16,18))
*OPC?
<read the reply>
Once the reply from the *OPC? query is read, all of the previous
relay operations have been completed.
The 1256 maintains an output buffer for sending replies to
commands. This buffer is 1024 characters in length.
Although unlikely, the output buffer could become filled with replies
to commands. If the output buffer is filled, the SCPI-defined
"QUERY Deadlock" condition will be detected by the 1256. In this
case, the output buffer will be cleared and an error will be added to
the error queue. In addition, the query error bit (QYE) of the IEEE-
488.2 Standard Event Status Register will be set. The error queue
may be read using the "SYST:ERR?" query, while the Standard
Event Status Register may be read using the *ESR? query.
When a reply is in the output queue, the message available, or
MAV, bit of the status byte is set. The status byte of the 1256 may
be read using the GPIB serial poll feature.
Publication No. 980855 Rev. A
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