1257 User Manual
SCPI Command Basics 5-26
EADS North America Defense
Test and Services, Inc.
©
2001
terminators, the 1257 will flush both input and output buffers and
then queue and error message.
Because the 1257 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 1257, and to ensure
that relays are in the programmed state, a query may be sent to
the 1257. 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 (@1(0))
OPEN
(@1(12))
CLOSE
(@1(17))
OPEN
(@1(16,18))
*OPC?
<read the reply>
Once the reply from the *OPC? query is read, all of the previous
relay operations have been completed.
Reply Output Buffer
The 1257 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 1257. 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 1257 may
be read using the GPIB serial poll feature.
