Triggers and how they work


 I am doing my best to learn the XEM3005 board.  I am currently using just the FrontPanel XML GUIs to do stuff (until I get a better grip on things).

 So, I have instantiated a counter that drives a 7-segment display.  The system divides the 50MHz input clock down to ~2Hz.  The 2Hz clock is used to drive the counter and also the ep_clock inputs to the trigger modules.

 When I send the trigger from the GUI, the counter starts counting as it should - I assume that only one trigger is making it to the hardware, but I honestly can't tell.

 When the count is done, it sends a trigger out on the falling edge of the ep_clock, and clears it on the next falling edge.  That is, (I think) I ensure that trigger is high for exactly one rising edge of ep_clock, and that there are no metastability issues (it's a 2Hz clock, after all).

 So, on the FrontPanel GUI, I have a triggersound and a triggerlog "device" set up.  What I am seeing (and hearing) is that I am getting *many* triggers back into the PC.  Not always the same amount (there seems to be an interaction with the GUI update speed), but usually around 40 or so of them.

 I could certainly use some help figuring out exactly what I am doing wrong.  I've done a couple of simulations to verify that I'm doing what I think I am, and it seems this is the case.  I have lots of pictures and project files available, if it helps.


Anyone have any ideas? Here is some more information:

First off, I am working from a schematic:

The 50MHz clock is divided down to ~2Hz by the “Divide50Mto2” block.

This 2Hz block is used to source the ep_clk inputs on the okTriggerIn and okTriggerOut modules.

When a TriggerIn is sent by the GUI, the TCount module counts 0-F hex, and then outputs a trigger pulse to the okTriggerOut module.

The simulation output of the TCount module is shown below (although at a much faster time scale - us instead of s)


So, there should be just one rising edge of the ep_clk while the TriggerOut signal is high. But, what I am seeingon the FrontPanel GUI is that there are many triggers coming back.

Here is a link to the GUI XML (Right-click and download)

Here is a video of what’s going on:

NewestTCountSim.jpg (36.8 KB)