E-TTL signal schema

I've searched quite a bit and can't find any data.

Just what is the ettl signal? Is it 2 way analog over 5 channels? I assume this is correct since the IR the system uses is just like TV remote signals.

The signal is obviously 2-way going from the meter in the camera to the flash and some data back. Correct?

Is there any data available online like a service manual for any EX camera etc. that can shed some light?

I saw the off shoe cord extension mod and got to think you could use a serial or ps/2 transceiver do to remote ettl where IR just doesn't cut it.

Do you know?

so no one knows if the communication is two way?

A little thinking about the matter would tell you it has to be bi-directional. Lens (and, with the 430 and 580 and compliant cameras sensor size) information is passed to the strobe along with firing commands, flash colour temperature (in the 430 and 580) and "Flash Ready" are passed back to the camera for starters. I seriously doubt that Canon service manuals would need to document the particular signals. They'd just use the appropriate diagnostic program to pump known commands into the camera or flash and verify the responses. You'd have to hook a modified OCS-2 up to an oscilloscope or similar to track the signals and decode them if you really want that info. Or you could just get a 6-channel transmitter/receiver (say from an RC model of some kind) and hook it up to pass the signals through.

Lets see, the flash will adjust when I zoom my 18-55 lens. The camera needs to know information about white balance from the flash. I assume the later, but I could be wrong.

This is exactly the transceiver I was thinking. Seeing the thread about extending the show cord got me thinking but of all the data I did not take into account "flash ready". Af assist, camera to flash lens length data etc.

Pocket wizards are great but no ettl...