Agilent Technologies 93000 SOC Series - Page 329

Lesson 3 – Setting Up the Digital Capturing
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Setting up the Levels
Levels for digital capture pins can be defined in the same way as
for standard digital output pins. This is done in the Level Setup
window.
When capturing digital data, for example, to obtain the generated
output codes of an ADC, typically not the quality of the output
signal levels is of interest (these would be tested with other tests),
but only whether a 1 or a 0 is received. Thus, a comparison with a
single threshold level is sufficient to determine the capture result
(1 or 0).
For digital capturing, you must set the high level threshold and the
low level threshold to the same value between the high output
level and the low output level of the capture pins. This way a clear
“1 or 0” distinction can be made.
Comparator Thresholds and Capture Results
Setting up the Timing
The timing for a capture pin can be defined in the same way and
with the same tools as for any other digital pin.
Setting up the timing for Digital Capture is different for the two
Capture Modes Sequential and Selective.
This is because in Sequential Mode capturing will be performed on
edges with normal compare actions, while in Selective Mode the
capturing will be performed on edges with a special ‘capture’
action, and will be explicitly avoided for edges with a special ‘do
not capture’ action.
NOTE In both modes, capturing can only be performed at single edges, that
is, capturing using window compare is not possible.