Re: PS/2 mouse as 1351?

From: Maciej Witkowiak (
Date: 2003-09-18 01:13:31

I would like to thank you all for suggestions.

Today I tried various configurations of pullups/pulldowns with single and
double inverters and it just didn't work most of the time, nothing reliable.
It seems that it makes almost no difference if there is an inverter or not.

Hársfalvi Levente dnia 17 wrz 2003 o 12:52 +0200 napisa³:
> >Are there any other options?
> Use the onboard comparitor of the AVR to trigger an interrupt at whatever 
> voltage level you set ;-). I'd at least do this. The comparitor has no 

Thanks! I will try it out tomorrow (today, actually).

Well, in either case I will prepare some documentation and put it all somewhere
online before October so others could play with it too while I can't (as my
holidays come to end).

> No, it's the other way (if it was that simple, I could have as well done it 
> on the 16c84 by bit-banging ;-) ). The clock is generated by the device, 
> and it's pretty fast. By itself, it could be done by bit-banging, but I 
> guess it's almost impossible to run it simultaneously with the also 
> time-sensitive 1351 emulation task.

It's hard to tell now. My idea was to use interrupts for both 1351 emulation
and PS/2 transfer (from two external sources, SPI and a timer) and do data
processing in the main loop. The two subsystems work when separated, I don't
know yet how will they coexist :). When irqs from POTX were triggered during
my experiments today I got almost correct values.

I have bit-banging routines for PS/2 too, just in case :). The clock on PS/2
changes every ~40us and it seems enough time to service timer irq that handles
1351 emulation (pulling up a line/both of them/releasing them).
It may be possible to handle it without SPI.


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