Peter Todd wrote:
> Wait, no that won't work, when the soft 5k pull up is enabled on the
> line, to allow the slaves to talk back, the LED's will effectively short
> the line, no good. They'll have to be behind the diode for sure.
> 
> Then again I could rely on the LEDs being off when communication needs
> to happen... but that would require the cooperation of all devices on
> the line.

- Master switches to soft pull-up
- LEDs short input
- Slaves detect this
- Slaves turn off LEDs
- Slaves and master wait until comms line rises again
- Communication begins

Sure, all devices have to turn the LEDs off, but you don't have to set 
up any funky synchronization or "slot" system. Is there a problem with 
requiring devices follow the spec? If reliability is a concern, then the 
original system won't work either - any slave stuck in a pull down data 
line condition would kill the bus for everyone.

Personally, I'd just use three wires, one for power. It makes things a 
lot easier.

-- 
Hector Martin (hector@marcansoft.com)
Public Key: http://www.marcansoft.com/marcan.asc

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