8251 troubles

[dwight elvey]

 Hi
  The routines SETUP and COUT are ROM routines.
SETUP passes the first byte to the clock generator and the
remaining to the command port of the 8251. The command/status
port is 1 while the data is 0.
 COUT sends text to a video board.
The second COUT never seems to get executed?? I give plenty
of time between characters because I send then manually.
 The board can do interrupt driven serial but that didn't seem to
work so I went for the simpler polling method.



         DI
          CALL SETUP
;         .DB    $01F  ; 9600
;         .DB    $01D  ; 4800
          .DB    $01B  ; 2400
;         .DB    $019  ; 1200
          .DB    $0AA  ; SYNC
          .DB    $0AA  ; SYNC
          .DB    $040  ; RESET
          .DB    $0CE  ;  2STOP, NO PARITY, 8BIT , X16
          .DB    $010  ; CLEAR ERRORS
          .DB    0

          MVI    A,$027  ; RTD, DTR AND REC-EN TX-EN
          OUT    1

          CALL   TIN

          CALL   COUT  ; This works

          CALL   TIN

          CALL   COUT ; never gets here
......................................

TIN:
          IN     1
          ANI    2
          JZ     TIN
          IN     0
          RET



> From: thrashbarg at kaput.homeunix.org
> To: cctalk at classiccmp.org
> Date: Mon, 28 Apr 2008 01:15:04 +0930
> Subject: Re: 8251 troubles
>
> On Sun, 2008-04-27 at 08:23 -0700, dwight elvey wrote:
>> Hi
>> I've got a funny problem with a 8251.
>> I've been writing 8080 code and seem to have a strange
>> problem.
>> I initialize the chip in async mode. I have a light box on the
>> serial wire. It is initialized to both send and recieve.
>> I send one character to the 8251 and it passes it to the software
>> on the 8080 side. I display it on the 8080 side.
>> I then send another character to the 8251. Nothing happens.
>> It won't receive until I reset it.
>> None of the status lights change. I can see the data light flicker.
>> It could be a bad part but it just doesn't seem that it would
>> work once and then fail to work for the second character.
>> It just doesn't make sense.
>> Is there something I'm missing about the 8251.
>> Dwight
>>
>
> That could be caused by a lot of things. Could you post the relevant
> code?
>

_________________________________________________________________
Express yourself wherever you are. Mobilize!
http://www.gowindowslive.com/Mobile/Landing/Messenger/Default.aspx?Locale=en-US?ocid=TAG_APRIL