Hello all,

I am using a 16F873 and have a working interrupt driven asynchronous 1/2
duplex USART with one problem.  I preload the TXREG with FFh as a dummy
character.  When TXEN is set and the PIC transmits the FFh, I get an error
in the receiving device.  It appears on the scope as if the baud rate
changes during the transmission of the first character.

I have used a W9x app to receive the dummy char as well as another embedded
(HC12) product.  I have loaded TXSTA with a literal word as well as set bits
individually as shown below with no difference.

Has anyone seen this situation before?


;TXREG preloaded with FFh

init_serial:
        BSF     STATUS, RP0     ;Select bank 1

        ;Using XTAL of 10.0000 MHz, BRGH=1:
        movlw   Baud38400       ;Select baud rate
        movwf   SPBRG           ;       /
        BSF     TXSTA,BRGH      ;High speed

        BSF     RCSTA,SPEN      ;Serial port enable

        BSF     STATUS, RP0     ;Select bank 1
        BSF     PIE1,RCIE       ;Enable receive interrupt

        BCF     STATUS, RP0     ;Select bank 0
        BSF     RCSTA,CREN      ;Enable Continuous Receiving

        BSF     STATUS, RP0     ;Select bank 1
        BSF     TXSTA,TXEN      ;enable transmit in serial port



John Gerthoffer
Software Engineer
American Auto-Matrix, Inc.
Smart Building Solutions
724/733-2000 x342

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