New acquisition...

Tony Duell wrote: Using a uPD7201 for the serial port is a strike against it. High speed modems that transport asynchronous data over a synchronous modulation, such as V.22, V.22bis, V.32, etc., have to use V.14 procedures to handle cases where the transmitting device is overspeed relative to the modulation, or the transmitting modem is overspeed relative to the receiving side. In the former case, up to one out of ten stop bits get dropped over the modulation, and reinserted on the receiving side. When that happens, or in the case that the transmitting system's modulation is faster than the receiving side (due to crystal tolerances, etc.), the receiving side is allowed to shave off a portion of each stop bit on the serial interface. That works fine with 99.9% of UARTs out there, which only require 9/16 of a stop bit for a valid receive character, and to start watching for the next start bit. The uPD7201 requires a full stop bit, so is not compliant with the V.14 standard, and will garble data and report framing errors when V.14 stop bit shortening occurs This was a huge problem for people using V.22bis or V.32 modems with the AT&T 7300 or 3B1 Unix PC, as they used the 7201. It's less of a problem since the adoption of V.42 error control, because when using V.42 there is normally hardware flow control at both ends, and V.42 can apply "back pressure" across the modem link to slow down a transmitting system as needed. Eric