Trigger multiflash on Canon 580 EX II flash

I have built a camera and flash trigger based on Arduino, and it is working well for me. I would like to use the multiflash capability on my Canon 580 EX II flash. If I trigger the flash from the camera or the button, I get a burst of flashes as programmed. If I trigger it from the Arduino, I get only a single flash. On the camera the shutter speed drives the time the multiple flashes will operate, I have tried various durations for the trigger pulse, from 50 to 1000 ms. Still get only a single flash. Can anyone help, please.

I'm assuming your trigger simply shorts the centre pin and side common.

Does the multiflash use the other pins on the hotshoe connector?

You could try googling for an explanation of the functions of the other pins, which I guess carry information about focal length and so on

Thanks for this response. I just short the centre to side, and the flash does use multiple pins on the hot shoe. I have since discovered that shorting the flash pins manually only produces a single flach and that multiflash is not supported on the PC terminal. That leaves me with two options: Program the Arduino to drive the multiple flashes or drive the flash via the hot shoe. Any ideas on where I can get the hot-shoe protocols?

Google turned up this:
http://kzar.net/wiki/Photo/CanonE-TTLProtocol