[stella] *Why* does the AtariVox work?

[Stephen Anthony]

On April 16, 2008 08:24:37 am Thomas Jentzsch wrote:
> Stephen wrote:
> > Yes, I know that seems like a strange question.  However, I don't
> > understand how writing SWACNT actually writes data to the
> > controller port.  I thought writing SWACNT only acted as a 'mask'
> > for further reads/writes done by SWCHA.  But it seems as if
> > actually setting SWACNT causes writes to be sent to the controller
> > port.  Is this correct?
>
> I don't think so. The code I have indicates that SWACNT is only used
> for masking. What makes you think that SWACNT causes writes?

OK, can someone trace the following code, stating what's in A after each 
instruction (and a brief description of why):

    lda #%11111111
    sta SWACNT

    lda #%11000011
    sta SWCHA

    lda #%00000000
    lda SWCHA

I think I know the issue, but I'd like confirmation.

Thanks,
Steve