28 Apr
2008
28 Apr
'08
2:22 p.m.
dwight elvey wrote:
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
I have the datasheet for the 8251A but not the 8251 here, so just some guesses:
- perhaps the 8251 (as opposed to the A) requires the receiver to be re-enabled
(not a full reset) after receipt of each character (an 'explicit ack') (?).
- .. check the error flags to see if a framing error is occurring?
- .. try sending a stream of (best random) characters at full rate,
as opposed to just 2 manually? This might get around some framing
inconsistency or such to at least see if a subsequent character can be received.
- (may be inconsequential, but in the init sequence the two sync characters
are not preceded by a mode byte (perhaps SETUP does this internally?))