TTL Trigger on USB-1024LS

[DaveWH]

Trying to get an event recorded in Cheetah neurophysiological software by sending the USB1024LS a TTL pulse (0 -> +5V) from scientific equipment. Nothing is recorded. If I send the USB-1024LS the sync out from a signal generator, the system works. What is different between a TTL pulse from a several pieces of equipment and the sync out from a signal generator. I can view the TTL pulsed on an oscilloscope, so they are being generated and sent to the USB-1024LS.

[DAQman]

The USB-1024LS is not a speedy device. It can be read about 100 times per second. The TTL pulse must be long enough for your program to read it.  What is the pulse duration from the scientific equipment, and is it the same as the signal generator?