I've been intending to collect information on hacking the Tomy iSobot, with the intention of replacing the stock controller with a new Propeller MCU. To this end, I'm going to measure the controller board and  the locations of the pins that plug into the arm and leg servo busses. The Prop chip will have a great advantage in driving the 5 serial busses (head, 2 arms and 2 legs) in that a cog can be devoted to each bus, leaving 3 cogs to run sensors and any nav or control programs.

Here's a translation of a Japanese site that has some inside information on the serial protocol. It appears to be 3.3V, 2400 bps, 0 start bit, 1 stop bit, with parity, no flow control. Packets seem to be 8 bytes, (LSB-first?) starting with [xFF][x05] followed by 6 variable bytes. Each leg has 5 servos, so each byte is presumed to control one servo and the last byte is the checksum of bytes 2-7.

Here's an image of the controller board- there are 3 wire pairs coming into plugs- the thicker is power from the Eneloop batteries, the lower right corner is labelled SPK1 (speaker) and the center top (under the power wires) is, hm, well, not labelled. I'll see if I can find the function later. On the left and right sides are 4 pin connectors, one for each arm; along the lower edge are two more 4 pin connectors for the legs, and in the center, a 6 pin connector. Not sure on the function of that one either right now. On the 4 pin connectors, VCC is the battery power (~3.7V), second pin is VDD (3.3V regulated), third pin is serial comm (Xmit only from MCU?) and fourth pin is GND.

I'm going to hook a Prop chip into the leg servo bus and try to monitor the data being sent while iSobot is making various moves, to see if I can confirm the translated Japanese findings.