A data and clock line? A PC keyboard works like that, albeit at about 10khz.
I've been pondering various solutions to the serin hang problem. In general terms, I wonder what is the most code efficient way of sending bytes from picaxe to picaxe using a protocol that does not hang?
There is the pulsout system - where a low is a short pulse and a high is a long pulse. It can work independently of any clock because the first byte can be 01010101 and the software can work out what is the length of a low and of a high and set a threshold half way between the two.
Then there is the data/clock system as mentioned. This ties up two lines - which is a bit of a pain for an 08/08M, but would not be such an issue for a 14M and only slightly more cost for 08M to 14M.
I'm sure there are other systems. Clock/data is a pretty standard system. I guess it needs a timeout so it doesn't hang waiting for a low to high transition. In terms of speed, the picaxe is probably slow enough that you could wait for a low to high transition on the clock line then just read the data line. Then start a do loop and wait for the next low to high transition, and also run a counter that times out. Just guessing ? about 1Khz.
I wonder what a common bus system might look like? Would a sending unit be responsible for generating the clock, or would you have a 555 making the clock pulses? Would you use a single picaxe pin for input and output? Would you 'wire or' onto the data bus with diodes?