Not getting right characters PS/2 Keyboard

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Not getting right characters PS/2 Keyboard

Postby lucidguppy » Sep Tue 06, 2005 9:31 pm

Assembly done today (same day I got the computer).

I'm not getting the right characters when I type on the PS/2 keyboard.

Not fun :-(

Has anyone else had this problem?

I've got the Serial Board Installed but not plugged into a computer.
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Postby vbriel » Sep Wed 07, 2005 5:58 am

Does the replica work without the serial I/O board installed (be sure to put the 6821 in its original socket to test this)?

I assume you built the kit? check all your solder connections. What exactly to you get when you type? if you type E000R what does the screen reply with?
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Postby lucidguppy » Sep Wed 07, 2005 6:55 pm

I'll just keep posting what I find as I debug the board.

1)Putting the 6821 back in did not solve the problem.
2)Examining the board with a microscope did not show any shorts - one joint looked bad but sufficient.
2)My 0-scope shows that the KBD CLOCK pin varies with what key I press and that KBD DATA does not - leading me to believe that the nets are either misnamed on the schematic or are swapped somehow.
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Postby lucidguppy » Sep Wed 07, 2005 7:16 pm

Different Keys produce other charachters like "return" would type "V" stuff like that. I think "1" is typed by pressing F6.

I ohmed out the PS/2 connector to the 8515.

The nets are correctly named as per the PS/2 spec but the traces go to the opposite pins.

Schematic:
KBD Data goes to pin 13
KBD Clock goes to pin 1

Reality:
KBD Data goes to 1.
KBD Clock goes to 13.

Is this the source of the problem? Was there a fix for that - and it didn't get into the manual?

If someone could tell me which key would produce AA or 55 on the KBD bus it would be much appreciated - that way I could check for shorts on the kbd bus.

Thanks,
LucidGuppy
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Postby vbriel » Sep Thu 08, 2005 3:15 pm

0x55 in 7 bit ASCII would be "U" decimal 55 would be "7".

Since you obviously have more electronic knowledge than many replica builders here's some things to verify if the ATMEGA8515 is decoding the ps/2 keyboard correctly:

Pin 28 is a strobe signal that is generated for about 28ms (if I remember correctly) everytime a key is pressed.

Pins 21-27 hold the data of the key last pressed even after the strobe signal. So, you should be able to decode you ASCII data from those pins. For example, if you press "A" on the ps/2 keyboard, it should show up on these pins as:
6 5 4 3 2 1 0
-------------
1 0 0 0 0 0 1

bit 0=pin21
bit 1=pin22
etc...
bit 6=pin27

when decoded is hex 0x41 or "A" in ASCII. You probably know this but I am posting it for those people that are learning digital electronics.

If you don't get a strobe signal from pin 28 or the data from those pins is incorrect the problem may be a bad ATMEGA8515 or in that area. Let me know what you find.

Vince
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Postby lucidguppy » Sep Thu 08, 2005 8:43 pm

Every time I type a character that will cause a strobe to assert - I get a pulse out for 4 milliseconds. If I hold the key down it repeats every 50 milliseconds.

When I type "L" no strobe occurs there are several other ascii compatible characters that don't cause a strobe to happen.

When I type "2" I see a U on the screen - I use the strobe as a trigger I see 55 appear on the keyboard bus. So the replica is seeing 55 and correctly putting up a "U" - but I think the 8515 is incorrectly interpreting the keyboard ps/2 stream.

I think I might have a incorrectly programmed chip.

Any word on the schematic discrepancy?
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Postby vbriel » Sep Thu 08, 2005 10:09 pm

Yes, that's a mistake in the schematic labeling of those two signals. The clock is pin 13 and the data is pin 1. Not sure how that happened. I agree that it is probably a misprogrammed 8515. Not sure how that happened or if it failed. It's possible one of the fuses didn't set properly and is running at the wrong speed. Anyways, drop me a private email and I'll get you another 8515.
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Postby lucidguppy » Oct Sun 02, 2005 8:20 pm

Couldn't get the computer to work with a new chip.
Couldn't get the computer to work with a new ps/2 keyboard.

Should I just get an ascii keyboard? Where can I get one of those?
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Postby lucidguppy » Oct Tue 04, 2005 7:02 am

I tied the reset to the 8515 to the master reset switch (not the ground side ;-) ) so that the chip resets when the computer resets.

Seems to be working now.

...now that its built...what do I do with it :?:
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