Hello Yves.
Sorry for me currently not having a CTR-502 at my hands.
Therefore I had to do some "copy and paste" from a project that I worked on in the late 2003.
I hope this VI is a helpful startup - although I could not test it before posting it to you (as already said: I don't have a CTR-502).
The VI is small, configurable and uses low CPU resources.
On a RT target like FieldPoint (FP) or compactFP this VI should typically run at least with "high priority".
I hope this will help in getting your job done.
BR, mgm