Re: Mouse interface stuff - K.O.?...

From: Martijn van Buul (
Date: 2000-09-18 15:25:06

Richard Atkinson wrote:
> I haven't looked into this as much as you, Levente, so forgive me if this
> is completely unhelpful, but: doesn't the fact that the PS/2 mouse uses a
> synchronous protocol clocked by the _host_ machine help? The docs might
> specify a fairly high clock rate, but you can (as far as I am aware)
> change it, and even send pulses at non-regular intervals; the state
> machine in the PS/2 mouse won't know...

That would make some sense. I'm not quite sure if this is historically
correct, but IIRC, the PS/2 bus was derivated from the ACCESS.bus (no
typo there), which was a joint-venture between Big Blue and Philips. 
The ACCESS.bus was supposed to be an overdressed version of I^2C.

I^2C is clearly clocked by the master. A slave can only *stretch* the
clock, not narrow it. I've written more_than_one software I2C implementations
(on both PC as well as 8051 platforms), using bitbanging. It all works fine,
as long as you don't have a multi-master setup (which isn't the case with
PS/2 mice)

    Martijn van Buul - -
	 Geek code: G--  - Visit OuterSpace: 3333
   Kees J. Bot: The sum of CPU power and user brain power is a constant.
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