Query Command - HP 54501A Programming Reference Manual

Query Command
Command
headers immediately followed by
a
question mark
(?)
are
queries. After receiving
a
query, the instrument interrogates the
requested function and places the answer in its
output queue.
The
answer
remains in the output queue until it
is
read
or
another command
is issued.
When read, the answer
is
transmitted
across
the
bus
to the designated
listener
(typically
a
controller).
The
query
:TIMEBASE:RANGE?
places
the current timebase setting in the output queue. The controller input
statement:
ENTER
<
device address
>
;Range
passes
the value
across
the bus to
the controller and places it in
the
variable Range.
Query commands
are used to find out how the instrument is currently
configured.
They are also used to get results
of measurements made by
the instrument, with the query actually activating the measurement.
For
example, the command
:MEASURE:RISETIME?
instructs
the
instrument to measure the risetime of
your waveform and place the result
in the output
queue.
Note
The
output queue must be read before
the next
pro/yam
message
is
sent.
For
example,
when you send
the query
:MEASURE:RISETIME?
you must follow that query with
the
program statement
ENTER
Value jisetime to read the result
of
the
query
and
place
the
result in
a
variable
(Value jisetime).
Sending another command before reading
the
result
of
the
query
will
cause the output
buffer
to
be cleared and the current
response to be
lost.
This will
also generate
an
error in the error
queue.
HP 54501A
Programming
Introduction to Programming an Oscilloscope
1-7