Can a M-series DAQ counter output drive a TTL input or 422A?

[Martin.D]

HI all,

We have a laser that we need to control via a digital pulse-train. We are using LabVIEW and a PCI-6220 card to generate a pulse-train using counters, and we can also generate the pulses using the standard digital outputs. The laser requires a "EIA RF422A" type input according to the manual (I think maybe this should read RS422 and not RF422!). I have been told that we can buy a chip that can convert TTL to the correct electrical standard for the laser. But It would be better if we could use the counters because of the triggering, does anyone know if the PCI-6220 counter output is TTL comapatible, or even EIA RS422A compatible? From the spec sheet it seems that the counter output can only deliver 75% of the required current in the logic low state. Do the NI counters comply with any electrical standards, such as RS422?

Any help would be much appreciated.

-Martin

[Henrik_Volkers]

You want to use the M Card DIO lines for a RS422 communication?

I wouldn't say it's impossible but why do all that UART stuff by your own?

Why not use a RS422 card? Or use an RS232 to RS422 converter?

You don't have to care about the protokoll/timing in your program and still can add the lines to 2 DI pins (via optocoupler?)  for measurements.

just my 2c

Message Edited by Henrik Volkers on 02-27-2006 02:44 PM

[Martin.D]

HI,

What the laser requires in this case is not really RS422 communication as you imagine it. All we need to do is send a series of pulses with a variable (pre-defined) duty cycle & frequency. Then stop the pulses using a digital trigger. The pulse width will be set between 10 micro seconds to 1 second. I only mention the 422A standard because it's the electrical compatibility that we are struggling with. I can not find the info I need in the NI specs because it's application specific I suppose.

Thanks.

[JamesC]

Hi Martin

If you can direct me to where you saw the 75% of TTL output you were talking about in your original post, I will check up on that for you.
However I am under the impression that the Counter Output on M-Series devices are TTL compatible.

Regards
JamesC
NIUK and Ireland

[Martin.D]

HI,

A contractor (NI-Alliance memeber) suggested to us that the counter output will only supply 75% of the TTL current in the logical low state. Since then we have tried driving a TTL input with the counter output and all seems to work very well. Although it would have been reassuring to find a document stating the compatibility.

Thank you.

-Martin