John Walshe wrote:
>
> I'm using an '876 with the onboard UART talking to an RF IC and a software
> UART(swuart) talking to the PC. On the PC I cobbled together a Visual C(++)
> application which sends commands to the PIC. However the PC talks too fast
> for the PIC to both grab the command data and do something with it. Although
> the shortest command is only four bytes long they come so fast on the tail
> of each other that the swuart misses part of the second byte and I get a
> garbled command.

I don't think you can ever guarantee how the PC will send your data,
especially time wise.

You didn't say what baud rate you are using, but I normally use 19200
and have no problems.

I use these 2 subroutines a lot for RS232 in/out.

;
; ----------------------------
; RECEIVE CHARACTER FROM RS232
; ----------------------------
; This routine does not return until a character is received.
;
Receive btfss PIR1,RCIF         ; (5) check for received data
        goto Receive
;
        movf RCREG,W
        return
;
; ------------------------------------
; WAIT UNTIL RS232 IS FINISHED SENDING
; ------------------------------------
;
TransWt movwf TXREG
        bsf STATUS,RP0
Wt_TX   btfss TXSTA,TRMT        ; (1) transmission is complete if hi
        goto Wt_TX
;
        clrf STATUS             ; RAM Page 0
        return


If you are expecting 4 bytes from the PC then perhaps...

        movlw Buffer
        movwf FSR
Rx_Loop call Receive
        movwf INDF
        incf FSR
        movlw Buffer + d'4'
        xorwf FSR,W
        btfss STATUS,Z
        goto Rx_Loop

        call TransWt            ; sends 0 byte back to ACK

        ; do something with data

Sending that buffer back again...

        movlw Buffer
        movwf FSR
Tx_Loop movf INDF,W
        call TransWt            ; guarantees byte is sent
        incf FSR
        movlw Buffer + d'4'
        xorwf FSR,W
        btfss STATUS,Z
        goto Tx_Loop

Basically make sure that your processing speed is OK with the baud rate
and vice versa.


--
Best regards

Tony

mICros
http://www.bubblesoftonline.com
mailto:sales@bubblesoftonline.com

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