maxtherabbit wrote on 2023-10-17, 14:02:

shamino wrote on 2023-10-17, 13:57:

rmay635703 wrote on 2023-10-16, 17:05:

It’s funny how the old pc repair shops always had a stack of spare keyboard controllers because people were always managing to kill them.

Unfortunate there isn’t a cheap ic you just buy, program and stick in

Back in the 90s I killed the mouse port on a socket-7 board by plugging the mouse header in backwards.

As luck would have it, that's the only socket-7 board I've ever encountered that still had a socketed keyboard controller chip. At the time I had no idea about this subject though, so it was never fixed. I need to replace that chip.

Very possible you didn't damage the KBC at all but instead you blew a fuse on the +5V line to the mouse port

I'll have to look at it sometime. But I do remember the mouse got hot, so I don't think the power cut off.

Let's go a little further down this road.

The 8042 and clones, are an integral part of the system. Not only it connects to the keyboard.

The Xstal at pins 2&3 is a necessary part of its design, but if it fails:
- non stable frequency: POST can become erratic close to lose sync and prevent it from following the tight timings for all the system to work (timer ko)
- dead: system won't POST but other funtions will be available (like Reset)
- xstal is always 8MHz? In some BIOS options I saw 7.xx MHZ, why is that?

Just a few things to have more fun with this.
All the boards I have sport one, at least I'll learn the signs of a bad crystal and what the speed may do.

Nexxen wrote on 2023-11-02, 01:55:

- xstal is always 8MHz? In some BIOS options I saw 7.xx MHZ, why is that?

I've noticed that too--that some chipsets can either run the keyboard clock at 7.16 MHz (i.e. 14.31818 / 2) or at some division of the CPU clock.

Why would you care so much about the exact KBC frequency? Why not just force it to 7.16 MHz as part of the design? The KBC clock needing to double for other purposes like power management/turbo, perhaps?

jakethompson1 wrote on 2023-11-04, 05:47:

Nexxen wrote on 2023-11-02, 01:55:

- xstal is always 8MHz? In some BIOS options I saw 7.xx MHZ, why is that?

I've noticed that too--that some chipsets can either run the keyboard clock at 7.16 MHz (i.e. 14.31818 / 2) or at some division of the CPU clock.

Why would you care so much about the exact KBC frequency? Why not just force it to 7.16 MHz as part of the design? The KBC clock needing to double for other purposes like power management/turbo, perhaps?

I'm trying to figure it out.
It's just a subject I'm interested in, 286 being in my youth's life 😀

I haven't found literature on how to implement it design wise, i.e. how to make it happen on a motherboard.
Probably it exists but isn't available on the net. Or a 1st year college manual has it and I'm a moron... 🤣

One thing I'm trying to learn is how to divide frequency from a crystal. The different crystals, and the importance of pF measure on capacitors in the xstal design to components.
There are tight timings that need to be in perfect sync, not all cap values are good. Stuff you learn on the way.

Nexxen wrote on 2023-11-04, 15:47:

One thing I'm trying to learn is how to divide frequency from a crystal. The different crystals, and the importance of pF measure on capacitors in the xstal design to components.
There are tight timings that need to be in perfect sync, not all cap values are good. Stuff you learn on the way.

There are some things the Jedi (Digital electronics) will never teach you, you must come to the dark side (analog electronics) 🤣 ... In particular I think you'll find some useful stuff out of the worldradiohistory dot org magazines and resources. Even if it's just copying the designs from the Elektor 101 circuits specials or something.