< Wouter van Ooijen asks> > Maybe you had an eralier PC than I ever used, IIRC my documentation > referred to a 8250. Is there any NS1645 datasheet on the web? Google did > not give me one. Good question, Wouter. I cheated when I wrote the email because I didn't actually remember the chip number. I went to the IBM "Blue Book" (IBM publication #6137806) and page 29 of the August 31, 1984, "Personal Computer AT Serial/Parallel Adapter," and transcribed the chip number -- NS16450. Your question sent me back to that reference to confirm the chip number. While there I went to another undated section entitled "IBM Asynchronous Communications Adapter" (IBM publication #6361501). On page 33 they show the 8250 chip. Quite frankly, I don't know which chip we had our adventures with. I'd assummed, incorrectly it appears, that the same UART was used on both adapters. Clearly, that's not so and I can't recall with authority which chip & adapter drove us nuts (I thought we'd had trouble with both). I do know that we got something like a half dozen of the first PCs and the "Blue Book" in our library directly from IBM for that project. However, in the final analysis I don't think it matters if handshaking is demanded by the hardware or software, it's not a good idea to build a RS-232 serial port device for widespread use without some accommodation for hardware handshaking. Knowing that it's someone else's fault is not much solace for a frustrated customer. Aza D. Oberman -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist