Here is a good video about communicating amongst multiple microcontrollers. In this case they are NerdKits that are distributing sign data so that a huge Multi-Panel LED Array can be built. Even if you aren’t interested in the project have a look at it for the SPI info.
“In this project, we put a new twist on our old idea, and modified the LED Array into a giant multi panel array — theoretically capable of driving 1200 LEDs (or more if you are creative!). The project uses the SPI bus to communicate between different chips, so in addition to the awesome new LED sign, we also go over how to use another useful piece of the ATmega168 microcontroller.”
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This can be highly serialized with cascaded shift registers driving the columns, and a 3 to 8 multiplexer driving mosfets to connect the rows to ground. Three lines for the multiplexer, three lines for the shift registers.
The IC count is about the same, but the code is all on one micro, with less I/O requirements.
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