>A little background first, I play (hobby) with home 
>automation.
> I run several Open Source projects (hence I'd like to keep 
> this
> on the real cheap, ie spend nothing as possible on tools). 
> I
> need to create a board that will convert X10 to Insteon (a
> translator of sorts). This is so I can replace a board 
> called
> the PL-Link (ASCII to RS485 to X10 converter) in the HCS 
> II.

I know you said you'd prefer hardware UARTs BUT if speed is 
OK you can produce multiple ones in software with relatively 
minor effort. A timer IRQ driven state machine that does NOT 
use per UART data based interrupts, essentially either runs 
fast enough or doesn't. ie is code dependant not data 
dependant. There are a few data rate related parts - like eg 
stacking data onto rotary stores, but that's not overly time 
intensive.

A major issue is the maximum desired UART data rate. IRQ 
rate needs to be several times higher than the minimum bit 
time. eg at 9600 baud ~= 100 uS/bit you'd want an IRQ of say 
25uS or less - even faster for more IRQ nibbles per data 
bit. You then need to look at available IRQ clock cycles to 
see if you can fit the code in.

One of the SX software peripherals implemented an N channel 
(8 max?) UART AFAIR and you could get some general ideas 
from there, even if the wholesale translation of the code is 
banned by the NDA you sign before you can access it.

Or you could even use an SX and have the code already 
written for you :-)

The task sounds easily enough doable by any number of the 
AVR ATMegas - code space is probably the only issue you need 
to check - and, of course, whether that variant was going to 
be available this time next year :-(.


        Russell



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