UART_SendChar
        bsf     STATUS,RP0              ; switch to bank 1
        btfss   TXSTA,1                 ; check TXMT flag and loop if
         goto   UART_SendChar           ; still not done sending the last character
        bcf     STATUS,RP0              ; switch back to bank 0
        movfw   UART_Tx                 ; put transmit value
        movwf   TXREG                   ; in transfer register
        return                          ; return from UART_SendChar


-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Olin Lathrop
Sent: Thursday, July 05, 2001 6:15 AM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [PIC]: F877 UART in ISR


>    I have moved a call of a PUTCHAR routine from the main code to within
the
> ISR and now it scrambles data.  I am polling TXSTA:TXMT to wait to send
the
> next character.  Any ideas?  Thanks!

First, this uses an additional stack location in the interrupt, which is
therefore not useable in the rest of the code.  I try to avoid calls as much
as possible in the interrupt routine.

> UART_SendChar
>         bsf     STATUS,RP0
>         btfss   TXSTA,1
>          goto   UART_SendChar
>         bcf     STATUS,RP0
>         movfw   UART_Tx
>         movwf   TXREG
>         return

USE COMMENTS!  I see a bug and possibly a misconception, which you probably
would have seen too if you forced yourself to describe the intent of each
line.  Good comments don't waste time, they save time.  If you don't care
about your code enough to document it, then why should I bother with it?


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, olin@embedinc.com, http://www.embedinc.com

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