Date   : Mon, 30 Dec 1985 12:31:47 EST
From   : mjs <@purdue.ARPA (Mike Spitzer):mjs@purdue-ecn-ee.ARPA>
Subject: Re: 8251 Usart

Thanks for your quick reply.  First of all, let me give you a little 
background about this computer(Royal Alphatronic PC).  According to Royal,
the only way to change the baud rate is by a hardwired jumper on the 
main PCB.  But, like I said, I've been able to change it as long as I
don't try to send data out. When I send something out, everything locks
up and I must do a cold boot.  This mystifies me, because everything that
I am doing seems to make sense.  Here's my setbaud.asm:


MCNTR  EQU     41H             ;Modem control port
RESET  EQU     01000000B       ;Value for port reset
MINIT1 EQU     01111010B       ;Value for 1 stop bit, even parity,
                                ; 7 data bits, 16X baud rate
MINIT2 EQU     00010101B       ;Value for Error reset, transmit 
                                ;enable, receive enable

       ORG     100H

INITIALISE:    MVI     A,RESET         ;Puts 8251 in instruction mode
               OUT     MCNTR           ;
               MVI     A,MINIT1        ;sets up baud, etc.
               OUT     MCNTR           ;
               MVI     A,MINIT2        ;Puts 8251 back in normal mode
               OUT     MCNTR
               JMP     0

This is pretty self explanatory, I guess... and it SHOULD work, but
there must be something that I'm missing... 

Let me know what you can come up with.

                                   Thanks again,
                                   Mike
                                            ihnp4!pur-ee!mjs