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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 6th Nov 2018, 4:59 pm   #1
McMurdo
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Default Another 486 PC keyboard problem

I thought I'd search thew forum before posting for help, this thread is similar but not quite the same:

https://www.vintage-radio.net/forum/...41&postcount=1


I'm also trying to get a 486-based machine working which has also lost its BIOS settings due to a flat bios battery.
This one says something along the lines of 'cmos battery error - default settings loaded..press CTRL-ALT-DEL to continue'.

The PC keyboard however is not used, and instead the MB provides the connector shown in the photo. I'm thinking if I can figure out how to connect the keyboard to this header, the rest will be easy.

The VGA monitor is also connected via a MB header, but luckily there is a coiled-up cable in the enclosure with the header at one end and the HD15 vga connector at the other.

So...my question is, might there be a way to 'scope' or trace out the keyboard pin out on this header? Other facilities on the header include the reset switch, keyboard disable switch and a programmable button matrix.
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Old 6th Nov 2018, 5:27 pm   #2
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Default Re: another 486 PC keyboard problem

Do you know that it uses a normal PC/AT keyboard/signals (albeit on an odd connector)?

The PC/AT keyboard has 4 connections. +5V, Ground, Clock, Data.

Finding +5V and Ground should be easy enough. If you knew which other 2 pins were used, even if you didn't kno which way round you could try it both ways and see what worked (there is no chance of damaging anything). But I wouldn't want to connect the keyboard clock or data line to a random signal.

Perhaps start by finding all pins that go to ground and +5V. The reset switch and keyboard disable switch will have one side grounded. Maybe you'll be lucky and find just one cluster of 4 pins that contains a ground and +5V and 2 other signals. If so then I'd try connecting the keyboard there.
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Old 6th Nov 2018, 7:04 pm   #3
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Default Re: another 486 PC keyboard problem

Might be worth a try, yes, I'm just terrified of damaging something. It's almost certainly an AT keyboard. It's really a very small SBC aimed at the industrial 'embedded pc' user, and comes with 'MSDOS-EMBEDDED' on a CF card.
The other pins used on the connector are likely the key (& led) matrix lines for driving a custom industrial control panel, which is how the board is currently configured.

The board, BTW, is from a rather obscure french manufacturer 'Aton Systeme' who, these days, trade under a different name,and specialise in automotive computers. The board type-number is unfortunately the same number as a very popular circuit board inside a very popular Samsung lcd TV, as google is happy to show.
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Old 6th Nov 2018, 7:52 pm   #4
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Default Re: another 486 PC keyboard problem

I'm fairly sure the PC sends out a short query messsage shortly after power-on, to which it expects to get a reply. When it doesn't see the reply, that's when the PC complains that it can't find the keyboard.

Here's a useful article about the physical and logical aspects of the PC-AT keyboard (and mouse) connections and protocol.

http://www.burtonsys.com/ps2_chapweske.htm
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Old 7th Nov 2018, 12:17 am   #5
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Default Re: Another 486 PC keyboard problem

It's possible that that header is meant to accept a ribbon cable, or a miniature header with crimp receptacles, with a pair of 6-pin PS/2-style sockets (not all pins are used) on the other end, for a standard keyboard and mouse.
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Old 7th Nov 2018, 1:22 am   #6
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Default Re: Another 486 PC keyboard problem

Indeed Julie, the last SBC I ordered (a Luke-something or other) came with a kit of header-pc cables for the various peripherals.
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Old 7th Nov 2018, 10:42 am   #7
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Default Re: Another 486 PC keyboard problem

Success! Following your advice, I identified the 5v and 0v, there were 2 pins for 5V and 5 pins for 0V. Looking at the way the keyboard and mouse operates, I read the clock and data have pullup resistors, and I figured they would use the same value for each; so I went along each pin and just 2 read 1K to the 5V rail, the others in the meg. range.
So, I went for broke and connected an AT keyboard. First time it didnt work, so I swapped clock and data, and it worked! Thanks all.
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Old 7th Nov 2018, 10:46 am   #8
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Default Re: Another 486 PC keyboard problem

Well done.
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Old 7th Nov 2018, 7:33 pm   #9
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Default Re: Another 486 PC keyboard problem

Result!
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Old 8th Nov 2018, 12:12 am   #10
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Default Re: Another 486 PC keyboard problem

Pride before a fall. It seems the FDD disc controller has failed.

If I try to load anything from FDD (or FDD emulator for that matter) or even try a format. the disc spins briefly and then reports 'floppy disc error'. It's the same for A & B drive.

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Old 8th Nov 2018, 12:57 am   #11
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Default Re: Another 486 PC keyboard problem

I had similar problems with my 486. I had to change out the floppy disk drive. The replacement intermittently reported errors, but it cured itself with use.

I would also see "Non-system disk" and 2Disk I/O" error messages both of which were down to problems with the disk rather than the disk drive.

Are the disk drives configured in the BIOS and connected to the correct connector on the twisted ribon cable?
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Old 8th Nov 2018, 1:04 am   #12
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Default Re: Another 486 PC keyboard problem

Yes, given that the BIOS settings were lost it may well have defaulted to expect a 5.25" disc drive.

The BIOS in my mid-nineties W95 laptop does that even though it is physically impossible to fit a 5.25" drive into the machine.
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Old 8th Nov 2018, 9:20 pm   #13
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Default Re: Another 486 PC keyboard problem

No, the bios default settings are for a 3.5in 1.44mb. The application software only uses drive 'A' so I used 'B' and set 'floppy swap' in the bios. The software then did the same when connected into the B connector (closest IDC connector to the motherboard).

The motherboard sees the floppy, puts the green light on and disc motor when I tell the software to format a disc, but only gives 2 little head motor grunts before waiting then timing out with a floppy fault.

The USB emulator does a similar thing, puts its green light on when disc is accessed but gives an error after so many seconds.
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