Re: Reading a synchronous input with an asynchronous device.

[Emmanuel Mayssat <emmanuel_mayssat@lynceantech.com>]

Additional info:

In my specific case, the signal to process is a diagnostic signal.
So it doesn't need to be read permanently. Let's say once every 30 sec, 
I process the input. Actually I was thinking about having another record 
to turn on or off the record processing.

I have 40 of those inputs.

A hardware solution would definitely be better, but because of space, 
cost, and time considerations it was decided that I, the software 
programmer, would take care of it.

--
E

Ned Arnold wrote:
> Two suggestions ...
>
> 1) Since you are looking for a transition, choose a TTL input module 
> whose inputs can be configured to generate an interrupt on a 
> transistion, have this interrupt process a calc record that simply 
> increments, and have another calc record that makes sure the first calc 
> record increments at least 100 times over a second (or 10 times every .1 
> second).
>
> 2) OR, add a little FPGA circuit (or a timer relay) that expects a 
> transition every 10 milliseconds (a simple watchdog) and use this output 
> to drive the digital input. This is preferred because it eliminates 
> 100Hz processing of records.
>
>
>     Ned