National Instruments 653 Series User Manual

Also see for 653 Series: User guide

Contents

National Instruments 653 Series User Manual Manual pdf 28 page image

Chapter 2 Using Your NI 653XNI 653X User Manual 2-8 ni.comSpecifying the Transfer RateIf you are internally generating the REQ signal, you must specify the datatransfer rate. The transfer rate is specified in software by using twoparameters, the timebase frequency and timebase divisor:wheretimebase frequency = 20 MHz, 10 MHz, 1 MHz, 100 kHz, 10 kHz,1 kHz, or 100 Hz, andtimebase divisor = an integer between 1 and 65,355.For example, if you specify a timebase of 100 kHz and a timebase divisorof 25, the resulting acquisition/generation rate would be 4 kHz because100 kHz/25 = 4 kHz.Note If you are using a version of NI-DAQ prior to version 6.8, the minimum value fortimebase divisor is 2.Note In LabVIEW, you can specify the transfer rate directly using Digital ClockConfig VI (called by DIO Start VI). The software chooses the closest transfer rate byselecting the frequency and divisor. To see the actual transfer rate, create an indicator at theactual clock frequency output of Digital Clock Config VI.Starting and Stopping Data Transfer—TriggeringBy default, data transfer starts upon a software command (the DigitalBuffer Control VI called by the DIO Start VI in LabVIEW and theDIG_Block_In and DIG_Block_Out functions in NI-DAQ C interface).However, you can use a hardware trigger to start, stop, or start and stop datatransfer. Trigger signals should be connected as inputs to the ACK1 and/orACK2 lines while in pattern I/O mode.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 datatransfer.Start TriggerA start trigger is a trigger that initiates a pattern I/O upon receipt of ahardware trigger on the ACK (STARTTRIG) pin.transfer rate (Hz) timebase frequencytimebase divisor----------------------------------------------=