Keithley 6430, Instruction Manual

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Data Flow C-3
Assuming that all functions are enabled, the data that is output by the read commands
(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 volt-
age, current and resistance readings as well as the timestamp and status information. Note that
if a measurement function is not enabled, then either the NAN (not a number) value or the
source reading will be used instead. See Section 17,
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 message “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 triggers 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 16 for more information on READ? and MEASure?.
CALCulate[1]:DATA?
If CALCulate1 is enabled, Sample Buffer data is fed to the CALC1 block where the results
for the selected math expression are calculated. The CALC1:DATA? command will read the
results of the math expression. If, for example, 20 data arrays in the Sample Buffer yield 10
math expression results, then CALC1:DATA? will acquire 10 readings (results).
CALCulate2:DATA?
If CALCulate2 is enabled, Sample Buffer data and CALC1 math expression results become
available to the CALC2 block for limit testing. Depending on the selected feed, limit testing
can be performed on the voltage, current, resistance, or timestamp readings of Sample Buffer
data, or it can be performed on the CALC1 math expression results. If NULL (rel) is enabled,
the readings used for limit testing will be the results of the null operation.
The CALCulate2:DATA? command acquires the readings used for limit testing.