So the PIC has no spare pins. Therefore to get a single wire serial bus to the device we must use the existing input wire and pin. The most common one wire bus is that of Dallas semiconductors and their 1-wire bus. No point reinventing the wheel (well not yet) so I plan to implement it on the PIC.
The 1-wire bus works by the master or slave device pulling the bus low for varying amounts of time to communicate 1's and 0's. No clock is required as each device is assumed to have a relatively stable clock source.
While reading the PIC datasheets I discovered a problems that will make the 1-wire bus difficult to implement. Pin-4, the one connected to the control wire has no output driver. It is an input only pin. This makes it impossible to pull the bus low.
Ok! So two options here. Put in a more modern micro-controller without these restrictions, like the Atmel ATtiny range. Unfortunately the power pins are not the same as the PIC - so messy rewiring needed.
The second is to change the pin. But there are no spare pins. Well actually the PIC has an internal RC oscillator, so the external 8MHz resonator isn't required. Yay two extra pins. One for the 1-wire bus and one for an LED too :).
Ofcourse this all depends on if I can actually reprogram the PIC.
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