User manual

2400 Series SourceMeter
®
User’s Manual Data Flow C-3
The SENSE block represents the basic measured readings of voltage, current,
and resistance. If Filter is enabled, the readings will be filtered. The SENSE block
also measures time for the timestamp.
When the INITiate command is sent, the programmed number of source-measure
operations are performed and the respective data is temporarily stored in the
Sample Buffer. For example, if 20 source-measure operations were performed,
then 20 sets of data will be stored in the Sample Buffer. Data from this buffer is
then routed to other enabled data flow blocks.
Assuming that all functions are enabled, the data that is output by the read com-
mands (FETCh?, CALC1:DATA?, CALC2:DATA?, TRACe:DATA?, and
CALC3:DATA?) depend on which data elements are selected. With all elements
selected, available data will include voltage, current and resistance readings as
well as the time stamp and status information. Note that if a measurement func-
tion is not enabled, then either the NAN (not a number) value or the source read-
ing will instead be used. (See Section 18, “FORMat subsystem,” for details).
After all source-measure operations are completed, the SourceMeter returns to
the idle state. The data stored in the Sample Buffer will remain there until data
from another source-measure cycle overwrites the buffer. Data in the Sample
Buffer is lost if the SourceMeter goes to the local state (REM annunciator off).
NOTE With no data in the Sample Buffer, the FETCh?, CALCulate1:DATA?,
and CALCulate2:DATA? commands to read data will display the mes
-
sage “Data corrupt or stale.”
FETCh?
This command is used to read data stored in the Sample Buffer. If, for example,
there are 20 data arrays stored in the Sample Buffer, then all 20 data arrays will
be sent to the computer when FETCh? is executed. Note that FETCh? does not
affect data in the Sample Buffer. Thus, subsequent executions of FETCh? acquire
the same data.
The READ? command performs an INITiate and then a FETCh? The INITiate trig-
gers a new source-measure cycle which puts new data in the Sample Buffer.
FETCh? reads that new data. The MEASure? command places the SourceMeter
in a “one-shot” source-measure mode and then performs a READ?. See
Section 17, “SCPI Signal Oriented Measurement Commands,” for more informa-
tion on READ? and MEASure?.