Hi Matthew...

Are you sure you don't really want a DCFSNZ instead of DECFSZ here in
set_tx_bit...

        bcf     INTCON, T0IF    ; Clear the interrupt flag
        decfsz  bit_count, F   <---- **** maybe you intended DCFSNZ??? ****
        incf    state, F        ; All the bits have been set, advance to the
next state.

Looks like maybe first time through you only send 1 bit, increment the state
to 4, and bail out.

-- Mark


> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu]On Behalf
> Of Matthew Miller
> Sent: Tuesday, May 13, 2008 9:08 PM
> To: PIC List
> Subject: [PIC] Help debugging a software UART routine.
>
>
> Hi everyone,
>
> In the past, members of the list have been good at pointing out
> programming
> mistakes that I've made and I hope this time is no different. :)
>
> I'm trying to learn how to create a software UART which I want to be
> interrupt driven. I have a transmit routine that uses delay loops written
> and it works fine. My attempt at an interrupt driven transmit doesn't work
> and here is the symptom: no matter what is transmitted, 0xFE is
> received. The RS-232 parameters are 1200N1.
>
> As a guide, the interrupt driven routine is named "trasmit" and
> the relevant
> labels in the ISR are uart_3 and uart_4. The delay based routine is named
> "transmit2" and this routine works (Coding this was my fall back after
> failing to get the "transmit" routine to work.) The main loop sends a
> sequence of bytes starting with '!'.
>
> I would be very grateful with being helped to discover my mistake(s). The
> program source code is attached.
>
> BTW: I found out the hard way that setting the OSCCAL value is very
> important for this kind of application!
>
> Thanks!  Matthew
>
> --
> "With reasonable men I will reason; with humane men I will plead; but to
> tyrants I will give no quarter."  -- William Lloyd
>



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