[Coco] 6551 at 115200 bps

[Roger Taylor]

At 05:20 PM 1/18/2009, you wrote:
>Roger,
>
>If you were to take the 1.8432MHz clock and feed it right into the
>6551's TxC and RxC (clock) pins and set the chip to external clock mode,
>you'd get 115,200 bps out of it.

And how would you do that?  I see a crystal but no oscillator or "clock".  ;)

And why does the 0000 mode (external clock mode?) also appear to 
yield 115200 bps when using the 1.8432 mhz crystal attached to the XTL pins?



>It's guaranteed up to 125k bps, meaning the fastest clock it can accept
>on those pins would be 2MHz.






>I'd guess the internal crystal oscillator isn't capable of reliably
>operating at 3.68MHz- but it may be possible to feed it with an external
>can oscillator. The guts of the thing are indeed capable of 115,200.
>
>
> > -----Original Message-----
> > From: coco-bounces at maltedmedia.com [mailto:coco-
> > bounces at maltedmedia.com] On Behalf Of Roger Taylor
> > Sent: Sunday, January 18, 2009 9:31 AM
> > To: CoCoList for Color Computer Enthusiasts
> > Subject: [Coco] 6551 at 115200 bps
> >
> >
> >
> > Has anyone noticed on Sock's website he mentions that doubling the
> > 6551 crystal value to 3.6864 mhz can be done but setting the 6551 to
> > the ExternalClock/16 mode would yield 115200 bps, then he says:  "
> > this *almost* works! "   Why wouldn't it work?
> >
> > We've proven that the CoCo can send and receive through the BITBANGER
> > port at 115.2 bps, and believe it or not - 230.4 kbps.
> >
> > Maybe Sock means that IRQ can't be triggered that fast and the CoCo
> > keep up?  Why not?  The 6551's IRQ goes to the CART signal which is
> > tied to FIRQ.  A circular buffer in the FIRQ service routine could do
> > a quick FIFO store to a buffer and it should work?  If not, the
> > crystal should probably be dropped to 1.8432 / 2  to yield a 57600
> > bps mode which should work.
> > --
> > Roger Taylor
> >
> > http://www.wordofthedayonline.com
> >
> >
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>
>
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-- 
Roger Taylor

http://www.wordofthedayonline.com