Read? And Measure? - Keithley 2520 User Manual

C-4 Data Flow

READ? and MEASure?

The READ? and MEASure? commands perform an INITiate and then a FETCh? The
INITiate command triggers a new source and measure cycle which puts new data in the
reading buffer after processing by the DSP. FETCh? reads that new processed data. See
Section 13
CALCulate1:DATA?, CALCulate2:DATA?, CALCulate3:DATA?
If CALCulate1, CALCulate2, or CALCulate3 is enabled, SENS1, SENS2, or SENS3 data
is fed to the CALC1 (laser diode), CALC2 (detector #1), or CALC2 (detector #2) block
where the results for the selected math function are calculated. The CALC1:DATA?,
CALC2:DATA?, or CALC3:DATA? command will read the results of the math function.
CALCulate4:DATA?
If CALC4 is enabled, the DSP subtracts individual A/D detector #2 readings from A/D
detector #1 readings, and then determines the pulse value or DC average over the pulse
width from this new set of delta values.
TRACe:DATA? and TRACe:DATA:VALue?
All normal readings returned by FETCh?, READ?, MEASure?, and CALCulateX:DATA?
are derived from samples acquired by a 14-bit A/D converter that samples at 10MHz rate.
An internal DSP section interprets the A/D samples over the pulse width in order to deter-
mine the pulse level value, or a DC average, which is stored in the reading buffer and then
sent back to the computer when requested by these commands.
With the TRACe subsystem you can bypass DSP calculations and directly query individ-
ual raw samples, allowing you to reconstruct a pulse to determine pulse parameters such
as settling times, overshoot, and undershoot. These samples can be requested by the
TRACe:DATA? query, which acquires all raw samples, and the :TRACe:DATA:VALue?
query, which requests specific samples.
See Section
for more information on READ? and MEASure?.
14, "TRACe subsystem," for details.
Model 2520 User's Manual