Re: Chip for PC Keyboard buffer

From: Michael Joosten (joost_at_c-lab.de)
Date: 03/18/04 

Date: Thu, 18 Mar 2004 18:59:00 +0100

Tauno Voipio wrote:
>
> Michael Joosten wrote:
> > Max wrote:
> >
> >>I want make a PC keyboard buffer to use PC keyboard with a long cable in an
> >>industrial enviroment.
> >>Does anyone suggest any chip to use?
> >
> >
> > Since I just read a data *** of an I2C repeater chip, and as it looks
> > like that the 8042/41 protocol looks very like the SCL/SDA signaling I2C
> > uses, why not just such a thingy?

>
> PC keyboard is *not* compatible with I2C. The protocol uses clock
> clamping, but in other ways it's nearer the asynchronous serial
> communication (commonly mis-called RS-232), but not compatible
> with that, either.

No doubt about that, but - I wrote REPEATER. And the thing is, in fact,
just a stupid repeater, no logic involved, just some (analog)
electronics (i.e. anti-parallel buffers). Whatever the real protocol is,
the chip does not care. And sorry, I should have used another word than
protocol, or rather put an 'electrical' ahead of it, to make it clearer.
I've only read a code for a software implementation of the PC keyboard
protocol, and I'm not sure if the clock line is also bidirectional, but
it probably needs to be...

Example (just google for I2C repeater):
http://www.e-lab.de/downloads/DOCs/PCA9515.pdf 

-- 
Michael Joosten, SBS C-LAB, joost@c-lab.de
Fuerstenallee 11, 33094 Paderborn, Germany
Phone: +49 5251 606127, Fax: +49 5251 606065
C-LAB is a cooperation of University Paderborn & SIEMENS