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Model 2701 User’s Manual Basic DMM Operation 3-59
Where appropriate
Since this query does not trigger a reading and can give duplicate results, there are not
many cases where this command should be used. The “:DATA:FRESh?” query (see page
3-47) is often a better choice. If this query is used, the following conditions should be met:
• A reading has been triggered either by free running (:INIT:CONT ON and
:TRIG:SOUR IMM), by some event such as a remote trigger (*TRG), or by an
external trigger (:TRIG:SOUR EXT).
• It is confirmed that the reading is completed, either by the setting of the RAV bit in
the status model or by allowing sufficient time to pass for the reading to complete.
:READ?
What it does
This command performs three actions. It will reset the trigger model to the idle layer
(equivalent to the :ABORt command), take the trigger model out of idle (equivalent to the
:INIT command), and return a reading (equivalent to a :FETCh? query). This command
will always return a new reading, since aborting the trigger model will invalidate any old
readings and trigger a new one. This query will “wait” for a new reading to become
available before the instrument sends a result back.
Limitations
This command will not work if the trigger source is set for BUS or EXTERNAL. This will
cause a –214, “Trigger deadlock” error. Under this condition, use a :FETCh? query or a
:DATA:FRESh? query (see page 3-60). If the trigger model is continuously initiating
(:INIT:CONT ON), sending this query may cause a –213, “Init ignored” error, but it will
still give a new reading.
When appropriate
If the instrument receives a *RST command, then it defaults to :INIT:CONT OFF,
:TRIG:SOUR IMM, and :TRIG:COUNT 1. Sending a :READ? query under these
conditions will trigger a new reading.
2701-900-01.book Page 59 Wednesday, August 3, 2011 9:43 AM