How do I get the difference in time using 2 ttl pulses

[Hideya]

Hi everyone,   I have a question using the delay time.  What I need to find the time interval between 2 incoming TTL pulses and fire the output TTL pulse precisely the same time interval after the second TTL pulse.  I have been using Labview 7.1 with real time module and FPGA module (I think 1.0 because I can not find wait for rising edge vi).  I am using NI 7830R card.  The length of each TTL pulse is about 1-5 microsec.  Second pulse comes in at about 1 millisec after the first one.  So I need to fire aboyut 1 millisec after the second incoming TTL pulse.  Because of the non constant TTL pulse length, I would like to reference at rising edge of incoming ttl pulses.  Can anyone give me a help on this?

Thank you very much.

Hideya 

[DavidEngr]

Hi Hideya,

As is the case with many programming questions, there are several ways to go about solving this one.  The solution I have in mind is to poll the digital input line for a transition from low to high.  The simplest way to do this would be to use a loop with a shift register to store the previous digital input value.  When the current digital input value is greater than the previous value, you can get the tick count (microsecond resolution sounds like it would be sufficient).  You can then do that sequence of operations a second time.  The difference between these two tick counts can be used as the input to the wait (microsecond) function.  After that you can send your digital output pulse.

Best regards,