Back in 08, the 168′s were the only Arduino compatible processor severely limited by its “single” USART. The Software serial library also took another year of developing before it became a viable alternative. This hardware solution is still by far the best and cheapest solution for increasing the number of USART’s for your (hobby) electronics project.

Dual USART is accomplished using a switch between both processors allowing either chip to be selected for programming. The two chips then communicate using the wire library, and the board I designed and manufactured has the i2c lines etched in with two inline 1.8k resistors. A sketch can be designed to run on one processor which utilizes both USART’s, or two sketches can be run that share USART device data.

@morcheeba

I had several dCore boards running for over a year (on and off, 7 days was initial constant trial period) and no problems with parts failing. Others that received boards reported no issues either, the processors remain syncronized and didn’t over-heat, cook, fry, cry, or burnout.

I also tested two RBBB’s and the power consumption was more or less the same as the single dCore.

So “if” your info is correct, then none of the characteristics you described presented themselves and that’s probably because the scale of the characteristics you described are inconsequential.

@Lupin

If it were as easy as joining two bulbs then I wouldn’t still be getting requests to this day from people asking for a copy of the sch and brd files. But it’s nice to minimize other people’s accomplishments, especially ones that are so conceptually simple that your kicking yourself for not having thought of it first.

Now I have a 328 version in production. That board will be shield compatible. The boards are for “my own use” as were the 168′s, and if someone has an issue with the concept then I suggest you invent your own better solution.

Concurrent firmware (on something other than the Propeller) would be interesting, though. :-)

This is like connecting two lamps in parallel and being surprised that both glow.

The better solution is a master/slave setup. One device will control the oscillator (connect XTAL1 and XTAL2 as usual) – this is the master. The other device is set up in “external oscillator” mode, with its input driven from the first. I looked at the spec sheet quickly, and it looks like XTAL2 is the output and XTAL1 is the input – this means you should connect XTAL2 of the master to XTAL1 of the slave. (you can verify this with an oscilliscope – the output waveform should be the squarer one)
—
On another note, I’ve thought it would be fun to take a 10 x 10 array of these tiny 100 MHz processors and make a 10GHz-equivalent computer on a 4×4″ pc board:

http://www.silabs.com/public/documents/tpub_doc/dshort/microcontrollers/small_form_factor/en/c8051f365_short.pdf

but, with limited communication, it could only run certain apps well.