No speek english me !!!!! 2008/5/10 Bob Estes <[EMAIL PROTECTED]>:
> > > Bob McConnell wrote: > >> James Knott wrote: >> >>> NoOp wrote: >>> >>>> On 05/07/2008 11:59 AM, James Knott wrote: >>>> >>>>> mike scott wrote: >>>>> >>>>>> On 6 May 2008 at 17:15, James Knott wrote: >>>>>> >>>>>>> Jerry Feldman wrote: >>>>>>> >>>>>>> >>>>>> ... >>>>>> >>>>>> >>>>>>> It was 1.5 stop bits back in 1976 when we were integrating a 1200bps >>>>>>>> modem into our POS system. I'm not talking about Baudot code. In any >>>>>>>> >>>>>>>> >>>>>>> ... >>>>>> >>>>>> >>>>>>> >>>>>>>> >>>>>>> It was never 1.5 stop bits for ASCII devices. It was either 2 stop >>>>>>> bits at 110 b/s or 1 at 300 & above. It wouldn't hurt anything, other >>>>>>> than >>>>>>> >>>>>>> >>>>>> I'm not sure that's correct. I'm pretty sure it was an option (1, 1.5, >>>>>> 2) on VAX serial ports. >>>>>> >>>>>> >>>>>> >>>>> The option may have been available, as it was on the 8250 UART used in >>>>> >>>>> >>>> >>>> I've a few of those, and 8251 USART's out in the garage... I know the >>>> 8251 could be configure to allow 1.5 stop bits, can't recall if the 8250 >>>> also had this option. However, 1.5 was only used for characters with 5 >>>> information bits, so it wouldn't apply to standard/modern modems anyway. >>>> >>>> >>> On the 8250 and later, you specified the number of data bits and stop >>> bits separately, so it was possible to have any combination of data bits and >>> stop bits. However, in all my years of experience with working with this >>> stuff, I have never, not once, seen 1.5 stop bits used with 8 bit codes. >>> It's always been either 1 or 2 stop bits, though 1.42 and 1.5 were common >>> with 5 bit codes. I've also never seen a UART that could do 1.42 stop bits, >>> which is found only on mechanical devices. A UART would be configured for >>> 1.5 stop bits, which isn't much of a difference from 1.42. So, while it is >>> technically possible to configure for 8 data bits and 1.5 stop bits, it's >>> never, to my knowledge, ever been done in production systems, as it doesn't >>> comply with any of the standard codes. As I mentioned in another note, this >>> is one area, having worked for 36 years in data communications and >>> computers, that I have a *LOT* of experience. In fact, when I designed & >>> built that 8 port serial card I mentioned earlier, I found a bug in the 8250 >>> that National Semiconductor didn't know about. I even got a nice letter >>> from them for finding it. >>> >> >> The fractionally longer stop bit was a carryover from the mechanical >> teleprinter days. Before synchronous motors became common, shaft speeds were >> controlled by a governor. No matter how carefully they were adjusted, there >> was always some variation between units. So the stop bit was lengthened to >> allow the slower device to stay in sync with each character. I believe this >> applied to all devices up through the early Model 28 equipment, somewhere in >> the mid 1950's. The extended bit was added to the transmit side of early >> electronic interfaces as well, just in case there was a mechanical device at >> the other end. Variations included 1.42, 1.5 and 2.0 bits. >> >> > The U.S. Navy was still using Model 28 teletypes in the mid to late 1960's, > and if I recall correctly, they had an extra long stop bit. (Either 1.5 or 2 > bits.) > > For more information about mechanical teletypes, here are some web sites >> and an active mailing list for former TTY repairmen like myself. >> >> <http://www.nadcomm.com/> >> <http://www.rtty.com/> >> <http://mailman.qth.net/mailman/listinfo/greenkeys> >> >> Bob McConnell >> N2SPP >> > > > --------------------------------------------------------------------- > To unsubscribe, e-mail: [EMAIL PROTECTED] > For additional commands, e-mail: [EMAIL PROTECTED] > >
