> ps2 interface ask pic as slave, it is really bad idea and occupied
> INT that brings lots trouble later.

Ok, I am afraid I must be guessing here, but I think you are saying:

"Using a PS/2 interface with the PICmicro as a slave is a really bad
idea and will occupy the interrupt handler which will bring a lot of
problems later on".

If this is not what you meant, please post what you meant, and ignore
the following response.

1) The PICmicro will always be a slave of the PS/2 device. The PS/2
device always generates its own clock: this is part of the protocol
and can't be avoided.
2) I am assuming you hook up the PS/2 clock line to a pin that can
handle interrupts, and set up the interrupt on the appropriate pin
change (LOW to HIGH, I think). The interrupt routine itself would be
quite short, as it would just shift the databit into the result
variable, and set a bit once a full byte is received, possibly copying
the shift buffer into a safe location so the next byte can be
received.

As far as I can tell this wouldn't really occupy the interrupt routine
much. apart from the context saving and loading it would take about
10-20 instructions. If you are really worried about the time spent in
the interrupt handler, you could just copy the one data bit to a
variable available in all banks: in that case you could do without the
context loading and saving, but your main routine would have to handle
the individual bits at a slightly faster rate (though still nothing
terrible).

If you have multiple interrupt sources you might have to build in an
additional check for the source of the interrupt and add appropriate
bit resets, but this is also trivial.

In short: I don't think it is a bad idea to do this, in fact, I think
it is a very good idea. Of course, when you have extremely time
critical code, like my NTSC generating stuff, you don't want any
interrupts at all. However, in most cases a 30 instruction interrupt
that occurs at most every 800 instructions (assuming a 4 MHz clock)
doesn't seem to bad.

Greetings,
Maarten Hofman.

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