I believe they are just modifoed bascic modules. The FX drives could receive/send ascii strings to communicate;
"DS1=1500" would set INDEX #1 distance to a value of 1500 (all integer) The resolution is set in the drive configuration.
You can find a manual on Emerson's site for "FX serial commands"
The AB end was alot of BTW/BTR commands and copies (I don't program AB's)