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New BIOS images (for original VT82C41N and implanted VT82C42) added. Both Y2K patched.

Great guide!

ph4nt0m wrote on 2021-06-21, 09:45:

It's better to install a 40-pin socket instead of soldering a 80C42 compatible controller directly to the board. […]
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It's better to install a 40-pin socket instead of soldering a 80C42 compatible controller directly to the board.

The 74LS06 inverter is basically for PS/2 mouse support. 80C42 can run in either AT or PS/2 mode while this VT80C41 can do AT only. Although once you've got a 80C42 working, there's no point in going back anyway. C5/C7 and L4/L5 values are not strictly specific though 100pF and 1uH are most commonly seen. Up to 1nF and 10uH should do.

All three TH_* pins (5, 25, 26) should be pulled up to +5V for normal operation. Otherwise it's really a matter of chance if a particular chip works well or not.

Thanks for putting all this info in one place anyway. This VT82C41 sucks. I guess the ROM inside isn't masked. OTP EPROM probably. May get corrupt over time. It's a pain in the arse to find a compatible 24-pin direct replacement. I'm not even sure a data sheet for it even exists.

Better later than nothings

I have a Board (LS486E of coruse 😀 ) with dead KBC.

This is my result after flying probing with DMM and desoldered KBC.

1vt82C41N pinout on LS486E /4S-1A
2
3PIN
41  NC
52  NC
63  CLK 8Mhz	I
74  NC	
85  8042CS	I
96  ioread	I
107  Address0	I
118  iowrite	IO
129  Data 4   IO
1310 Data 3	IO
1411 Data 2	IO
1512 Data 1	IO
1613 Data 0	IO
1714 GND	
1815 Data 5  IO
1916 Data 6	IO
2017 Data 7 	IO
2118 NC
2219 KEYLOCK 	I
2320 IRQ1 	O
2421 KBCData 	I 
2522 KBCClock I
2623 NC
2724 VCC

A note: KBC data input & output is combined into one port, no 7406 is requiered.