[cctalk] Re: RS232 - parallel modems!?

Hi Steve, In my opinion that article leaves a LOT to be desired from a technical standpoint. I think a lot of the stuff he states as facts are misleading at best. I remember when those came out. IIRC they were mostly marketed toward laptops without serial ports. But as stated some desktops did use problematic (slow) 8250 UARTs which had trouble over 9600bps. Writing to a UART (e.g. 8250, 16450, etc) is in general faster than writing to a parallel port. For the uart, you simply write a byte and you're done. As you say, for the parallel port, you write the data, then you have to write the control port to turn on strobe, then write the control port again to turn it off, possibly with (short) delays in between. You probably need to read a status from both to see if the port is ready, but that is similar in both cases. Reading is even worse. A "standard" parallel port only had 4(or 5) input bits so you had to read at least twice to get a byte. Also, many of the pins were open collector (resistor pullups) intended to drive longish external cables, so that made the parallel port itself relatively slow. But plenty fast for V34. > So.. If you had a slow system that couldn't really take advantage of a > ~7MHz 16550 serial card (or I guess like a laptop that was stuck with an > older UART) That might be the use-case where this parallel v.fast might > help (by being able to "feed the modem" fast enough to actually take > advantage of the faster modem speed?) Or is there some other scenario As hinted at above, it is probably a faster system (cpu wise) that could do the best with a parallel modem. Keep in mind, the modem MUST have the equivalent of a uart built in. But three writes for each byte and probably 3 or 4 reads per byte will slow down a slower computer. > NOTE, in the articled linked above, it does mention that it is only "value > added" if you have this parallel-modem on both sides of the connection. > (this is because you'll be flow controlled to whatever is the slower device > in the connection?) Reading that stuff made me wonder if microcom was paying him. I find that a wee bit fishy. Anyway. My 1/2 cent worth. Will