My customer has a device that only communicates via COM ports...how does Acu-COBOL Extend handle this?  And it doesn't have to be with the API if a better way is available.

You did not indicate if communication is only to the device or if it is bi-directional. (I also assume you are using Windows)

For the former you can simply set use MODE to set the communication parameters (eg MODE COM1:96,N,8,1) and write to the porrt (as if it were a file); You will also need a "null modem" cable;  ie flow-control bridged out.

The later will require the API (ACURS32.DLL) with or without flow control.

I have used both successfully in many applications over the past 20 years.