Specifying The Transfer Rate; Starting And Stopping Data Transfer-Triggering - National Instruments 653 Series User Manual

Chapter 2 Using Your NI 653X

Specifying the Transfer Rate

If you are using a version of NI-DAQ prior to version 6.8, the minimum value for
Note
timebase divisor is 2.
Note In LabVIEW, you can specify the transfer rate directly using Digital Clock
Config VI (called by DIO Start VI). The software chooses the closest transfer rate by
selecting the frequency and divisor. To see the actual transfer rate, create an indicator at the
actual clock frequency output of Digital Clock Config VI.
Starting and Stopping Data Transfer—Triggering
Note The NI 653X supports triggering only in pattern I/0 mode. In handshaking mode,
you cannot use triggering because the handshaking lines are used to start and stop the data
transfer.
NI 653X User Manual
If you are internally generating the REQ signal, you must specify the data
transfer rate. The transfer rate is specified in software by using two
parameters, the timebase frequency and timebase divisor:
transfer rate (Hz)
where
timebase frequency = 20 MHz, 10 MHz, 1 MHz, 100 kHz, 10 kHz,
1 kHz, or 100 Hz, and
timebase divisor = an integer between 1 and 65,355.
For example, if you specify a timebase of 100 kHz and a timebase divisor
of 25, the resulting acquisition/generation rate would be 4 kHz because
100 kHz/25 = 4 kHz.
By default, data transfer starts upon a software command (the Digital
Buffer Control VI called by the DIO Start VI in LabVIEW and the
and
DIG_Block_In DIG_Block_Out
However, you can use a hardware trigger to start, stop, or start and stop data
transfer. Trigger signals should be connected as inputs to the ACK1 and/or
ACK2 lines while in pattern I/O mode.
Start Trigger
A start trigger is a trigger that initiates a pattern I/O upon receipt of a
hardware trigger on the ACK (STARTTRIG) pin.
timebase frequency
= --------------------------------------------- -
timebase divisor
functions in NI-DAQ C interface).
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