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From: rap@oliven.UUCP (Robert A. Pease)
Newsgroups: net.micro.pc
Subject: Re: Running IBM serial boards at 19.2KB
Message-ID: <842@oliven.UUCP>
Date: Fri, 10-May-85 16:09:29 EDT
Article-I.D.: oliven.842
Posted: Fri May 10 16:09:29 1985
Date-Received: Tue, 14-May-85 06:40:00 EDT
References: <145@cernvax.UUCP> <138@omen.UUCP> <535@cyb-eng.UUCP>, <122@kontron.UUCP> <1141@ecsvax.UUCP>
Organization: Olivetti ATC, Cupertino, Ca
Lines: 38

.

> Warning! Running your IBM PCs serial port at 19200 may be hazardous
> to it's health!. I am just passing this on but I am reliably informed
> that the reason IBM does not specify serial operation at 19.2 is that
> it is under some circumstances possible to burn out the UART chip.
> The reason may be that internal currents in MOS curcuits are often
> directly related to switching frequency.
> 
> This is not to say you can't do it, in fact I have linked my PC to my
> Data General One at 19200 baud and got away with it .. but for how long
> that will last I don't know. Data General has a program for c
> communicating to the PC which works up to 19200 baud but they reccomend
> only using at 9600 for this very reason.
> 
> Mike Gingell,  ITT Raleigh, NC (919) 878 8100  ..decvax!mcnc!ecsvax!mjg

Out darned spot!  Point one; the 8250 is perfectly capable of running at
19.2K baud.  I quote from the NS data sheet for the INS8250-B;

	o Fully Programmable Serial-Interface Characteristics
	  --  5-, 6-, 7-, or 8-Bit Characters
	  --  Even, Odd, or No-Parity Bit Generation and Detection
	  --  1-, 1&1/2-, or 2-Stop Bit Generation
	  --  Baud Rate Generation (DC to 56k Baud)
				    ^^^^^^^^^^^^^^

Point  two;  MS-DOS  (and  therefore  PC-DOS)  runs  the  primary  and
secondary async ports !without! interupts.  This means that it is very
easy to lose characters!  Especially if running at higher baud  rates.
This  is  why  it  is recomended not to try serial port communications
above 9600 baud.  My recomendation is that if you want to  go  faster,
write  yourself  an  interupt  driven  RS-232  serial port driver that
accepts XON/XOFF protocols and use it.  Then go knock yourself out!
-- 

					Robert A. Pease
    {hplabs|zehntel|fortune|ios|tolerant|allegra|tymix}!oliveb!oliven!rap