Ralf.Brown@B.GP.CS.CMU.EDU (07/15/88)
In article <4200004@hpihoah.HP.COM>, bruce@hpihoah.HP.COM (Bruce LaVigne) writes: }actually stuff into the chip are divisors of an externally input clock. With }the clock that IBM used, if you go above 9600 you start using non-integer }divisors. What this means is that since you can really only use integer }numbers into the chip as a divisor, you don't get 19200 but something kindof }close. If the other side can handle it, fine, but IBM doesn't support it. That is not correct. The divisor for 9600 is 12, so the divisor for 19200 is 6 and for 38400 it is 3. As a matter of fact, it is the 110 baud that is off by a small fraction of a percent, whereas 300/600/1200/2400/etc are all exact (assuming that the clock is exact). However, from what I have heard, early 8250's had problems sync'ing with the incoming signal at >19200. I believe that the various 115k transfer programs use two stop bits to help the chip recognize the incoming data. -- UUCP: {ucbvax,harvard}!cs.cmu.edu!ralf -=-=-=- Voice: (412) 268-3053 (school) ARPA: ralf@cs.cmu.edu BIT: ralf%cs.cmu.edu@CMUCCVMA FIDO: Ralf Brown 1:129/31 Disclaimer? I |Ducharm's Axiom: If you view your problem closely enough claimed something?| you will recognize yourself as part of the problem.
charles@hpcvca.HP.COM (Charles Brown) (07/23/88)
>Just what I meant. The 'kindof close' depends on the input-clock to >the 8250. As all PC-compatibles will use it, no problem will occur >because the 'kindof close' will be the same everywhere. If some fancy >machine which claims to be compatible uses a different clock rate, it >might not be able to communicate with others, and, more important, >many programs won`t work as soon as they program the chip directly >(setting the divisor with the same value won`t achieve the same results). > Peter Lipp (plipp@tugiig.uucp) Your attitude assumes that the IBM PC is the only computer in the world or at least the only important one. Disgusting! It is clear that you have never used a *real* computer. -- Charles Brown My employer is not responsible for my opinions.