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To ensure compatibility with other NI devices, configure trigger pulses on an NI PXI Express device to last for at least two clock cycles of the clock on the receiving device. For example, if the clock on the receiving device is 8 MHz, which is a clock period of 12.5 nanoseconds, the trigger line must be constant for at least 25 nanoseconds, which is two clock cycles of an 8 MHz clock.
|Note Regardless of the clock speed, pulses on the trigger line must be constant for at least 18 nanoseconds.|
The clocks between an NI PXI Express device and another device may not be perfectly synchronized. If you assert a trigger line on an NI PXI Express device, you cannot determine at what point in the clock period the trigger registers in the receiving flip-flop. If the trigger arrives during the setup or hold time of the receiving flip-flop, you cannot determine the state of the line for that clock period. Asserting the trigger pulse for two clock cycles ensures that at least one clock cycle on the receiving flip-flop registers as a rising edge and transfers as a trigger.
PXI Specification Tutorial—Refer to this page on ni.com/white-papers for more information about trigger timing parameters.