Measurement Computing PCM-D24/CTR3 rev.3 - Manual (Page 21)

This diagram shows schematically the programmable options.
Because of the limited number of pins on the 33 pin connector, all signals from all
three counters are not available externally. This is compensated for by the ability to
chain counters and control the count source.
Clock Source Select
The source for count pulses to the inputs of the clocks may be controlled via software.
The counter source will be overidden by counter linking (see below).
External Clock 2 - Supplied at pin 31 1
1 MHz Clock 0
Clock Scource Counter 2 CKSEL2
1 MHz Clock 1
10 MHz Clock 0
Clock Source Counter 1 CHSEL1
External Clock 0 - supplied at pin 28 1
10MHz Clock 0
Clock Source Counter 0 CKSEL0
Counter Linking
Counters may be linked into 32 or 48 bit depth. Note that counter linking overrides
counter source select for counters 1 and 2.
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