What you want then is a MITS SIO-B. Has a COM2502. That generation of chips trade extreme simplicity for dip switches and loads of support chips. When I build and use serial I look at a few things: Chip count < the fewer I have to wirewrap the better> Functions I want <Vs gobs of unused features> Availability (are they in my stock) Usually I end up with 8253 countertimer as BRG and 8251, or 8250. Though the 6850 is friendly enough. I also have others to pick Allison