Engineering Design NIDisk Guide de l'utilisateur télécharger pdf (Page 22)

NIDisk User Guide

4. Acquisition or playback will begin on receipt of the external trigger signal.

Triggering an External System from NIDisk

Output triggering allows the user to initiate some process in an external system at the

beginning or end of acquisition or playback in NIDisk, in order to synchronize the NIDisk

I/O process with an external system. For example, the user can start a playback in NIDisk,

then use the output trigger signal to trigger an external neurophysiological data acquisition

system. To gather "pre-trigger" data, insert a segment of silence at the beginning of the

NIDisk playback signal.

Synchronization signal

The output synchronization signal is called IO_ACTIVE. It goes HIGH at the beginning of

the I/O process and LOW at the end of the process. These rising and falling edges can be

used to inform the external system of the beginning and the end of the I/O process. Note:

NIDisk issues synchronization signals only with manual triggering only, not with

external triggering.

Synchronization signal latency

Synchronization signal latency is the time delay between the beginning of the I/O process and

the rising edge of the synchronization signal (and between the end of the I/O process and the

sync signal's falling edge). IO_ACTIVE rises within about 20 microseconds after the

beginning of acquisition or playback, depending on CPU speed (measured with a DAQCard-

6062E on a Pentium-III/650).

The latency of the falling edge of IO_ACTIVE varies between 70 and 600 microseconds

(measured with a DAQCard-6062E on a Pentium-III/650) on playback. IO_ACTIVE latency

on acquisition has not been measured but is probably similar.

IO_ACTIVE connection

If you have an Engineering Design (ED) I/O panel with the digital I/O option, IO_ACTIVE is

provided at the TRIG OUT connector on the panel. If your ED panel does not have this

connector, contact ED for modification options.

If you are using a National Instruments (NI) I/O panel, IO_ACTIVE is provided at pin DIO-

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Engineering Design NIDisk Guide de l'utilisateur Page 22