Toby,

I take it that you are new to PICs.

You can send/receive 38400 just fine with a PIC, although it DOES take some
ingenuity on storing the data.

I have done just that, but unfortunately the storage routine is not
disclosable.  Suffice it to say that it's not especially easy.

Now, for the send/receive code.  Note that the code assumes the PC is
transmitting 8,n,2 (not 1 stop) to give time to save the data.  Also, data
is sent and receivd on the same pin in this project, although that is not
necessary.

;***************************************************************************
***********************************************
;
;       UART_TX
;
;       Transmit W at 38400 out XBIT, 8,N,1 protocol.
;
; INPUTS:
;       W
;
; OUTPUTS:
;       n/a
;
; USES:
;       Timer
;       temp1
;       temp2
;
UART_TX
:Speed_Delay_1  equ     9               ; 9 passes * 3uS per pass + 1
:Speed_Delay_2  equ     4               ; 26-14 overhead=38

        clrwdt
        movwf   temp1

        movlw   8
        movwf   temp2

        bsf     XBIT                    ; Force STOP BIT condition initially
        movlw   TRIS_RB_TX              ; Set port to transmit
        tris    RB                      ; Set as an output now

        movlw   :Speed_Delay_1
        movwf   Timer:LSB
        bcf     XBIT                    ; Send START bit
:Loop1  decfsz  Timer:LSB,F
        goto    :Loop1

:Loop   btfss   temp1.0                 ; Send DATA bits
        bcf     XBIT
        btfsc   temp1.0
        bsf     XBIT

        goto    $+1                     ; Waste four cycles to pad to exactly 13
        goto    $+1
        nop

        movlw   :Speed_Delay_2
        movwf   Timer:LSB
:Loop2  decfsz  Timer:LSB,F
        goto    :Loop2

        rrf     temp1,F                 ; Set up for next bit
        decfsz  temp2,F                 ; Done yet?
        goto    :Loop                   ;       No, repeat

        movlw   :Speed_Delay_1          ; Send STOP bit
        movwf   Timer:LSB
        bsf     XBIT
:Loop3  decfsz  Timer:LSB,F
        goto    :Loop3

        movlw   TRIS_RB_RX              ; Set port to receive now
        tris    RB
        retlw   0
;
;........................................
;
;       UART_RX
;
;       Receive char at 38400 in XBIT, 8,N,2 protocol.
;
;       NOTE:  We don't stick around for the stop bit!  We should therefore
;       have about 40uS to process the received character before the leading
;       edge of the next start bit.
;
; INPUTS:
;       none (but RB must be set for input on XBIT pin)
;
; OUTPUTS:
;       temp1 = character received
;
; USES:
;       Timer
;       temp1
;       temp2
;
UART_RX
:FullBitTime    equ     4               ; 26 uS

        clrf    temp1                   ; character received
        movlw   9                       ; bits to read in (start gets shifted ou
t)
        movwf   temp2

:WaitStart                              ; Wait for leading edge of start bit
        clrwdt
        btfsc   XBIT
        goto    :WaitStart
        goto    $+1
        goto    $+1
        btfsc   XBIT                    ; Start bit still there?
        goto    :WaitStart              ;       No, start over waiting - it was
noise
                                        ;       Yes...

:Loop   bcf     C
        rrf     temp1,F
        btfsc   XBIT                    ; Sample bit, stuff into character buffe
r
        bsf     temp1.7
        movlw   :FullBitTime
        movwf   Timer:LSB
        nop
        nop
:BitWt  nop
        decfsz  Timer:LSB,F             ; Wait 1 bit time (just a few instructio
ns short...)
        goto    :BitWt
        decfsz  temp2,F                 ; Dec bit counter
                                        ; Done?
        goto    :Loop                   ;       No, loop
        retlw   0                       ;       Yes, return with char in temp1
;
;........................................
;
;       UART_ChkIdle
;
;       Wait for 2 character times of idle on receiver pin
;
;       Character Time @ 38400 = 10x26 uS
;       --> we need to wait 520uS min.
;       520uS / 5uS per pass = 104 passes
UART_ChkIdle
        movlw   104
        movwf   Timer:LSB
:Loop   clrwdt
        btfss   XBIT                    ; Transmitter "idle" right now?
        goto    UART_ChkIdle            ; No, reset timer
        decfsz  Timer:LSB,F             ; Timer expired?
        goto    :Loop                   ;       No, check bit again
        retlw   0                       ;       Yes, back to caller
;
;........................................




At 12:14 PM 12/14/98 -0700, you wrote:
>I would like a 16F84@4MHz or a 12C671@10MHz to communicate with a PC at
high speed (my goal is 38.4 kbps).  The software uart given in AN555 from
microchip says it can provide 4800 baud @ 4MHz or 19200 @ 10MHz.  I am
wondering if I can buy a separate hardware uart (usart?) and get better
performance (with simpler software)?  Any leads to where I can find
examples/suggestions/help?

==================================================================
Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
==================================================================