Modifications for 16 bit triggers

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David Horton

Modifications for 16 bit triggers

Post by David Horton » Wed Mar 14, 2007 11:30 pm

Hi there,

I have recently completed several modifications to the ActiView source code in LabView, allowing for a TCP connection to be established to a remote machine. With these changes, I am able to receive trigger values from the remote computer over the network, and they are being properly displayed via the trigger screen subvi, and are also properly stored when recording to a bdf file.

The only problem occurs when I try to receive trigger values that exceed 7 bits (128+). Since ActiView is designed to separate the hi and lo bytes of the status channel, is there a straightforward way to combine them and allow for large trigger values to be properly displayed and recorded? I anticipate having to alter the trigger screen vi and possibly do some bit swapping, but I wanted to inquire here first.

Thanks in advance!

David

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Post by Coen » Thu Mar 15, 2007 5:54 pm

ActiView only separates the triggers into two bytes for display purposes; the 16 trigger lines are always stored as in the BDF file as 16 independent bits (see http://www.biosemi.com/faq/trigger_signals.htm)

The analog trigger display mode shows all the 16 lines as colored bars. Displaying the triggers as 16 bit words (0 to 65535) would require some minor changes to the code.

You are probably aware of it, but I want to stress again that you cannot use triggers received by TCP/IP for accurate timing purposes (there is not fixed timing relation between the events in ActiView and the "real world", because of the variable delays introduced by the USB transfer, ringbuffer, and Windows OS). For accurate timed triggers, the use of the trigger port on the USB receiver is the only option.

Best regards, Coen (BioSemi)

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