User's Manual

Chapter 2 Function Reference — WFM_ClockRate
NI-DAQ FRM for PC Compatibles 2-408
© National Instruments Corporation
The only internal timebases available on the E Series devices are 20 MHz and 100 kHz. If
you use a timebase other than –3 or 2 for these devices, NI-DAQ performs the appropriate
translation, if possible.
Note If you are using an SCXI-1200 with remote SCXI, the maximum rate depends on
the baud rate setting and updateRate. Refer to the SCXI-1200 User Manual for
more details.
mode depends on the whichclock parameter.
Range: 0, 1, or 2 for E Series devices.
0 or 1 for the AT-MIO-16X and AT-MIO-64F-5.
0 for all other devices.
whichclock = 0:
When whichclock is 0 (update clock), mode should be 0 for all other devices except for
E Series devices. For these devices, mode is used to indicate the time of change of update rate,
when a waveform is already in progress. If no waveform is in progress, mode is ignored. Set
argument mode to 0 to indicate that you wish to change the update rate immediately. For
E Series devices you cannot change the update rate when using FIFO pulsed waveform
generation and waveform is already in progress.
whichclock = 1:
When whichclock is 1 (delay clock), mode indicates whether delay clock should be enabled
or disabled. When mode is 1, NI-DAQ enables the delay clock. If you want to use FIFO
pulse-waveform generation, you must set mode to 1. Notice that, if you enable delay clock,
you must load finite iterations. If you load infinite iterations, NI-DAQ returns error code
fifoModeError.
whichclock = 2:
mode is ignored in this case.
whichclock = 3:
Mode is ignored in this case.
If any of these conditions is not met, NI-DAQ returns updateRateChangeError.
Using This Function
You can calculate the actual update rate in seconds from the timebase resolution selected by
timebase and interval, as shown by the following example.
Suppose that timebase equals 2. On an MIO device, this value selects the 100 kHz internal
clock signal, which provides counter 2 with a rising edge to count every 10 µs, thus selecting
the 10 µs resolution. On Lab and 1200 Series analog output devices, if the total update interval
given by (timebase resolution)
*
interval is greater than 65,535 µs, it programs counter B0