> But mosts mouses wakes up in a standard config, and I
> don't think one *have* to write to them, generaly speaking.

You are completely right. There is no need to write if you want to use
them, and if you do decide to write to them, you end up in a quagmire
of non-standard protocols. Setting things like resolution and update
speed are still doable, but the more fancy stuff (like scroll wheels)
uses a different mechanism for each mouse.

Even if you DO decide to use them bidirectionally, you still can't use
the SPI protocol, because with PS/2 the peripheral always controls the
clock (the PICmicro can pull the clock low and deny communication, or
switch to transmit mode, but once you start sending, the mouse will
provide the clock to the PICmicro).

Greetings,
Maarten Hofman.

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