>Your start bit is currently half a bit-time long; make it a full bit-
>time (in other words, replace the "call Delay50uS" with a "call
>Delay100uS") and everything will work MUCH better.
>
>-Andy

Well, this is confusing - your suggestion doesn't work.

The frustrating part for me is that I still don't have a definitive reference for whether the start bit is 1.5t, 1t or 0.5t, and of what polarity relative to the stop bit. Does anyone have a pointer to an actual rs232 standard that shows these relationships? I know the voltages and pinouts - but what *exactly* is supposed to take place from the start of transmission to the very end? Even an ugly ASCII art diagram would be great.

Is this supposed to be right for sending H'28' at 9600/n/8/1?

1       156uS <start bit
0       104uS <bit0
1       104uS
0       104uS
0       104uS
0       104uS
0       104uS
0       104uS
1       104uS <bit7
0       104uS <stop bit

The above doesn't seem to work in my case. Reversing start/stop polarity also doesn't work. Only when I shorten the start bit to 50uS does it work somewhat reliably, and only when I lengthen the stop bit 3x-5x does it seem solid. Like so:

0 52uS ;start bit
bit0 104uS
bit1 104uS
...
bit7 104uS
0 104uS ;stop bit
0 104uS ;stop bit
0 104uS ;stop bit
0 104uS ;stop bit

Code follows (delays are properly adjusted to give very close to correct bit times in this routine):

Sendbyte:
        movwf   MYBYTE
        bsf     PORTA,dataout   ;startbit 1/2t logic low
        call    Delay50uS
        movlw   D'8'
        movwf   BITCNT
bitlp:
        rrf     MYBYTE,f        ;lsb first
        btfss   STATUS,C
        goto    sendlow
sendhigh:
        bcf     PORTA,dataout   ;direct-connect so invert
        goto    bitset
sendlow:
        bsf     PORTA,dataout
        goto    bitset          ;this would fall through, but
                                ;keeps bit timing symmetrical
bitset:
        call    Delay100uS      ;1t each bit
        decfsz  BITCNT,f
        goto    bitlp
        bcf     PORTA,dataout   ;stop bit 1t logic high
        call    Delay100uS
        call    Delay100uS
        call    Delay100uS
        call    Delay100uS
        call    Delay100uS
        return