Hello;
In case you are using a higher TimeBase clock as the source input of the counter, you can't use the lower frequency Timebase.
The Timebase clock source is the same internal counter, in hardware, that gets divided down in case you need to operate with the lower frequency. Anyway, the source is the same, therefore you can't use both Timebase frequences at the same time.
Regards
Filipe A.
Applications Engineer
National Instruments