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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.

Madao wrote on 2024-06-22, 17:38:

Better later than nothings […]
Show full quote

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. […]
Show full quote

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.

Copy code to clipboard

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.

I don't think you got the data pins in the right order. You're also missing reset. I probed mine and came up with this:
Via VT82C41N DIP-24 Keyboard Controller (KBC) - help completing pinout

I'm pretty sure it's right because I designed a ps/2 mod board which converts the DIP-24 footprint to use a standard DIP-40 KBC, and it works.

This pins I marked as ??? are actually just N/C

I have mine running with an AMD 5x86-133 CPU Over clocked at 160mhz
Very Stable and Running Win95b

These Motherboards were popular back when Win95 was released
Computer stores were selling them as an inexpensive upgrade for 386 and 486 computers
So they could better run Win95

It was popular to sell these motherboards with the AMD 5x86 CPU for about $150 USD.

Intel486dx33 wrote on 2025-03-06, 18:46:

I have mine running with an AMD 5x86-133 CPU Over clocked at 160mhz

So do I.
With implanted PS/2 mouse and 64MB EDO RAM. Windows 98SE works pretty fine except freezing on reboot. Shutdown however works as expected and I see "Safe to turn off blah-blah-blah"

Madao wrote on 2024-06-22, 17:38:

Better later than nothings […]
Show full quote

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. […]
Show full quote

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.

Copy code to clipboard

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.

That's a more correct mapping of 80C41 to 80C42:

pin 1: NC
pin 2: NC
pin 3: input clock -> pin 140 of SiS 497 (SYSCLK)
pin 4: RESET_L
pin 5: CS_L
pin 6: RD_L
pin 7: A0
pin 8: WR_L
pin 9: D3
pin 10: D4
pin 11: D5
pin 12: D6
pin 13: D7
pin 14: earth
pin 15: D2
pin 16: D1
pin 17: D0
pin 18: NC
pin 19: P17 (keylock)
pin 20: P24 (IRQ1)
pin 21: KBDI (keyboard data)
pin 22: KBDC (keyboard clock)
pin 23: NC
pin 24: +5V

A 486DX33 was my very first PC during university days, and I wanted to get a system like that. I was looking for a 486 motherboard with onboard features (IDE, com ports etc) and PCI slot (for video), and came across exactly this one (I rescued from a recycling center). Kind of hard to find documentation on it: this board is on Retroweb, however no manual... using the advanced search with slots as parameters, I found an identical one which seems to be a duplicated entry (although with a different naming). It has a a partial manual which helped me set it up, and currently is running Memtest using an AMD DX4-100.

In case anyone needs, link to the manual (on the "twin board", which is exactly the same as the Lucky Star LS-486E Rev:D 2SIMM)
https://theretroweb.com/motherboards/s/lucky- … 6ed-rev:2a#docs

I will add this mod later to my project list. For now, I can manage a PS/2 mouse with an adapter to COM1 (already tested and it worked).

I forgot how hard is to run such systems, no CD booting etc (which I solved using a Promise IDE card).

I looked around but didn't find... what is the HDD size limit for this hardware using the motherboard IDE ports (2GB? 10GB?32GB?64GB?). I tried a 128GB HDD and of course it doesn't boot. I can try smaller sizes later (I have different adapters and some legacy HDD).

Aladim wrote on 2025-04-18, 21:17:

I looked around but didn't find... what is the HDD size limit for this hardware using the motherboard IDE ports (2GB? 10GB?32GB?64GB?). I tried a 128GB HDD and of course it doesn't boot. I can try smaller sizes later (I have different adapters and some legacy HDD).

8G works but 40G does't. So it's somewhere in between.

Aladim wrote on 2025-04-18, 21:17:

I looked around but didn't find... what is the HDD size limit for this hardware using the motherboard IDE ports (2GB? 10GB?32GB?64GB?). I tried a 128GB HDD and of course it doesn't boot. I can try smaller sizes later (I have different adapters and some legacy HDD).

8GB CF to IDE works fine, but IDE in SiS496 is poor. It's in the north bridge and yet not on the PCI bus. No DMA, PIO only, so you better disable this mediocrity and keep using your PCI IDE card unless it's a DOS only build.