Hi CEK -
Your answer lies in the
NI-DAQmx Help. The counters on your DAQ device are paired, and certain operations require a pair of counters instead of just one. When you generate a
finite number of samples, the driver must use a pair of counters, so if you select Ctr0 it'll automatically grab Ctr1 along with it. When you generate
one sample or
continuous samples, only one counter is needed.
This is a hardware design limitation that can't be overcome, except by installing a second DAQ device or a device with several counters (like the 6602, 6608, or 6624).
David Staab, CLA
Staff Systems Engineer
National Instruments