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

From: Richard Atkinson (
Date: 2000-09-18 13:08:40

On Sun, 17 Sep 2000, Hársfalvi Levente wrote:

> As speaking of the PS/2 mouse plan, after reading the specs (thanks to
> Richard) I see it'll reveal much more problems in the code than the
> RS-232 (async) communication ever had :-(. The problem is, the bitrate
> is quite high. According to the docs, the bit time is about 30-50
> microseconds. I can delay the byte transmit even for several
> milliseconds, but unfortunately not during transmitting a byte
> (transmitting a particular bit in a byte can't be delayed). During
> generating the duty cycle for the POTX/POTY inputs for the SID in 1351
> mode, the microcontroller can be off even for 140-150 cycles (because of
> the needed exact timing). (One cycle corresponds to one microsecond @ 4
> Mhz osc clock). 'Of course', the PIC16c84 has no SPI interface or
> similar toy, one has to do everything by software. Bit banging rulez
> like hell... :-/

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...


Richard Atkinson
Software Engineer
Tenison Technology EDA Ltd

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