SNAP-SCM-485-422 start of message character



I have a SNAP-SCM-485-422 that I want to use to control a Yokogawa UT-150 tempature controller. In the documentation for the UT-150 it specifies the start of message character as Chr$(2). The documentation for the SNAP-SCM-485-422 says that the start bit cannot be configured but I can not find what start bit it uses.

I’m just trying to verify that the start bit isn’t going to be a problem.



Hello Andrew,

Welcome to the OptoForums!

Looking at this UT100 series communications manual, specifically pages 10 & 16, I think you’re confusing:
configuration settings (baud rate, stop bit, etc.) with the command/packet, which you’ll build and send with your control strategy created using PAC Control.

You can set & save your module’s baud rate, etc., using PAC Manager under Tools > Inspect > Communications > Serial Modules, select your Serial Module number there from the drop-down (I’m showing module 7 here), and configure as needed:

Then save that config also in PAC Manager under Inspect > Status Write, choose “Store configuration to flash” and click “Send Command.”

Then you’ll use a communication handle variable in your PAC Control strategy to build that command (starting with the 2). Check out this post on Comm Handles 101.

When you build your string, if you’re using OptoScript it might look something like this:

sCommand = chr(2) + chr(nUT150Address) + chr(1) + chr(0) + chr(nThisCommand) + ....

Or if you’re using regular instruction blocks, you’d use the Append Character to String command:

Looks like you’ll also need the built-in Generate Checksum on String command as you finish building your command/packet.

I hope that helps!