AVR-Chat

Paul Maddox wrote:
> Dave,
>
>> Can you do clocked serial on a couple of pins, maybe in a ring, or
>> share clock and separate data lines?
>
> I could, though There will be other stuff going on, so I'd rather not
> have to depend on bit banging.

I would think twice.
The processing cycles overhead to produce a 4800 bps software UART
(big-bang) is no more than a 1% in a 4MHz AVR (considering 8 instructions to
manage each serial bit), could say even half percent in a 8MHz AVR.  Well, I
see you want to intercommunicate 2 or 3 uCs at 192kbps, for that I would
develop my own protocol in burst mode, synchronous data frames, CRCs, etc,
something dedicated for the application.  Bit-bang for that speed is an
overkill, consider 4 channels running at 25%, will be an equivalent of a
constant 400kbps data flow, a 8MHz core will deliver no more than 20
instructions per each serial bit period of time, impossible to do anything
else.


>> Does everyone need to talk to everyone, or master to two slaves, or ?
>
> two fo the four ports come from outside, for these I planned to use
> the built in USARTs.
> The other two are slaves from the master, so I could use my own
> 'serial' ports by bit banging, but I'd rather avoid the over head if
> possible. Ideally I'd love a dual UART chip with buffer :-)
>
> Paul



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