About Remote Control
COMMANDS
AND QUERIES
Warning or error messages are normally not reported by the instru-
ment, unless the controller explicitly examines the relevant status
register, or if the status enable registers have been set in such a way
that the controller can be interrupted when an error occurs. The
status registers are explained in Section 7.
During the development of the control program it is possible to
observe all remote control transactions, including error messages,
on an external monitor connected to the RS-232-C port. Refer to
the command "COMM_HELP" for further details.
Program messages consist of one or several commands or queries.
A command directs the instrument to change its state, e.g. to
change its time base or vertical sensitivity. A query asks the instru-
ment about its state. Very often, the same mnemonic is used for a
command and a query, the query being identified by a <?> after
the last character.
For example, to change the time base to 2 msec/div, the controller
should send the following command to the instrument
TIME DIV 2 MS
To ask the instrument about its time base, this query should be
sent
TIME DIV?
A query causes the instrument to send a response message. The
control program should read this message with a "read" instruc-
tion to the GPIB or RS-232-C interface of the controller. The
response message to the query above might be
TIME DIV 10 NS
m
The portion of the query preceding the question mark is repeated
as part of the response message. If desired, this text may be sup-
pressed with the command "COMM_HEADER".
Depending on the state of the instrument and the computation to
be done, the controller may have to wait up to several seconds for
a response. Command interpretation does not have priority over
other oscilloscope activities. It is therefore judicious to set the con-
troller IO timeout conditions to 3 or more seconds. In addition, it
must be remembered that an incorrect query message will not gen-
erate a response message.
4
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