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From: yawei@bronze.ucs.indiana.edu (mr. yawei)
Newsgroups: comp.os.msdos.programmer
Subject: Re: Setting BAUD rate with MODE command
Message-ID: <1991Jan10.182440.20564@bronze.ucs.indiana.edu>
Date: 10 Jan 91 18:24:40 GMT
References: <10764@darkstar.ucsc.edu> <24200010@b-mrda.ca.boeing.com>
Organization: Indiana University, Bloomington
Lines: 20


Setting the baudrate divisor in UART to 6 would give you a 19200 baud
rate. (Doubles the divisor halves the baudrate, etc.)  The baud rate
divisor is a 16bit register, with high byte at port 3F9h(Com1:) and 
low byte at 3F8h. Bit 7 of line control register must be on when 
accessing the baudrate divisor.

To set Com1: to 19200b, 8data bits, 1 stop bits, no parity, do:

  Send 80h to 3FBh         ;line control register
  Send 00h to 3F9h         ;high byte
  Send 06h to 3F8h         ;low byte
  Send 03h to 3FBh         ;8 data bits, etc.

The base address (3F8h) of com1 can be found at 0040:0000, and com2
at 0040:0002. It is a better idea to get it from here than just assume
it to be 3F8h etc, as it allows softwares that swap com ports to work.

Ya-Gui Wei
a.k.a. yawei