Date   : Mon, 06 Jan 1986 19:57:08 EST
From   : Mike Spitzer <inuxc!pur-ee!mjs@ucb-vax.ARPA>
Subject: Thanks for you help with the 8251

Thanks for all of your help with the 8251.  My problem was with the 
number that I was sending to put the chip back in "normal" mode
after initializing.  I also need a dummy read from the data port after
initializing.  Thanks to mknox@ngp.UTEXAS for sending me the
right number to use.   The following code works fine for me:

;MODEM PORT EQUATES
MCNTR  EQU     41H             ;Modem control port
MDATA  EQU     40H
RESET  EQU     01000000B       ;Value for port reset
MINIT1 EQU     01111110B       ;Modem init value for baud, etc
MINIT2 EQU     00110111B       ;puts it back in "normal" mode
;               ^^^^^^^^^ this is what I changed

       ORG     100H

INITIALISE:    MVI     A,RESET         ;Puts 8251 in instruction mode
               OUT     MCNTR           ;
               NOP
               NOP
               MVI     A,MINIT1        ;sets up baud, etc.
               OUT     MCNTR           ;
               NOP
               NOP
               MVI     A,MINIT2        ;Puts 8251 back in normal mode
               OUT     MCNTR
               NOP
               NOP
               IN      MDATA ; I added this line to my original code
               JMP     0               ; the warm-boot didn't hurt anything

If anyone is interested in a rather large collection of hints for 
programming the 8251, let me know via mail and I'll send it to you.

              Thanks again,
             
                 Mike -- mjs@purdue-ecn -- pur-ee!mjs