View Full Version : A1200 1D1 Mobo - Keyboard controler failure?

2nd August 2012, 23:20
Hi to everyone,
I got an A1200 1D1 mobo with a strange behaviour. So when connecting a keyboard (tried 2) and pressing a key, after releasing it still inputting the pressed character (as it was jammed). Everything works fine except this "small" defect. Anyone had this kind if problem or/and know how to solve it? Or I have to send it to the nearest trash can :blased:

3rd August 2012, 01:52
This is more suited to the Amioracle section :)

When a key is depressed, a 7-bit code is sent by the MPU. When it is released, the same code plus $80 (8-th bit set) is sent. Codes are sent to odd-CIA's SP-register ($BFEC01 - 8 bits) where they are read by the keyboard driver to determine what's going on with the keyboard.

So either the MPU is not transmitting the plus-$80 code when a key is released, or the respective up/down bit in $BFEC01 register is broken and always reads as 0.

Both are really weird things to go wrong though.

You can test by disconnecting the A1200 keyboard and e.g. plugging a Lyra2 adapter onto the MPU and using an external PC keyboard. The Lyra2 will correctly produce up/down keycodes right on the MPU's data pin, effectively replacing the MPU in its job.
(The PC Key 1200 adapter is NOT suitable for this kind of test. The adapter must clip onto the MPU.
If you have an Amiga external keyboard, you can connect the 4 wires right to the respective MPU pins with the same effect. Same goes if you have an A500 keyboard, get the pinouts and you're good to go.)

So if it works you know it's the MPU. If the results are the same, it must be the odd-CIA chip. Swap the two CIA-chips and observe.

20th August 2012, 14:13
Hi again,
That was the MPU. Took a closer look and found that someone tried to solder /probably some kind keyboard upgrade/ and made it without care. Between two legs must have been some sort of micro short circuit. I cleaned all carefully and voila.
Thanks for your help BLTCON0 :thumbsup: :)

21st August 2012, 17:24
Glad it's sorted out :) yes that kind of "keyboard upgrades" seems rather common but carries a bit of a risk. At least the MPU wasn't damaged :thumbsup: