oh, ok......
Here is two other possilbe simple solutions, one you do the other buy off the shelf stuff.......
1). since you only need a voltage to send, at start up of m3, (or on changes?)
convert your voltage to a BYTE format, and send each BIT if it is a 1, to one
of m3's 8 OUTPUTs, this could be an standard piece of CAT5 cable wiht RJ's on each end.
in your hardware, you look at the pattern of on/off on the 8 wires, and rebuild the byte,
and convert it back to a number, that represents you voltage.
You could put an "Init" macro in mach that would pull the starting voltage from a DRO,
on your screen, converts it to a BYTE, sends it as 8 output lines each line representing one BIT.
Your hardware reads the value, converts it to a number, and sets the voltage with it.
1A). If you did need to make a run time change of the voltage, just put a screen button,
that has the "sending code" discussed above, your hardware could note that the value
in its register has changed, and set to volt to a new level.
2). Off the shelf solutions, use PLC with analog card (I have used ADC DL05 with analog card for THC, you can ajdust the PID
loop as well, so that you can elimitate "Dive" and get intellegent control), cost of that is about 300.00 US funds.
2A). Since you might want other intellegent IO, try a MESA board. The stuff like the PK, MODIO, Modbus board, are tied to some kind of continual update loop, for there analog outputs. The PK, I could put a "run once" in it on an analog or IO pattern for you. BUT, I think fx issolation would be an ongoing issue with the Plazma.
3). As a side note: Brian released a "General Serial" plugin template, you could download and modify that for your needs.
or pay some poor sap like me, or Steve, or Ed to do it for you, or yourself.....hehehhee.
scott