Yes, this is a thread for a different adapter, but there are also other similar projects. Such as my project NeoG mentioned. Unless you specifically want rio444's ISA card, I also have an extra prototype for that that I could send to somebody in EU. This is also quite easy to solder, as it has through hole components.

Internal PS/2 to serial mouse adapter

The primary difference between these approaches is that PS/2 to serial converters need modified drivers for achieving low latency and being able to work with quirky KVM switches, but rio444's ISA card does not as it just pretends to be a serial port. The downside for rio444's card is that it's more difficult to solder, the chips need to be programmed (well, microcontroller in PS/2 to serial converters needs to be programmed as well, but AVR programmers are incredibly cheap on Aliexpress) and BOM is also a bit more expensive.

Mike_ wrote on 2026-06-18, 07:54:

Yes, this is a thread for a different adapter, but there are also other similar projects. Such as my project NeoG mentioned. Unless you specifically want rio444's ISA card, I also have an extra prototype for that that I could send to somebody in EU. This is also quite easy to solder, as it has through hole components.

Internal PS/2 to serial mouse adapter

The primary difference between these approaches is that PS/2 to serial converters need modified drivers for achieving low latency and being able to work with quirky KVM switches, but rio444's ISA card does not as it just pretends to be a serial port. The downside for rio444's card is that it's more difficult to solder, the chips need to be programmed (well, microcontroller in PS/2 to serial converters needs to be programmed as well, but AVR programmers are incredibly cheap on Aliexpress) and BOM is also a bit more expensive.

I saw your thread and your adapter. My issue is I cannot get my serial port working with a mouse, so no Windows 3.1 for me. It has an AT keyboard port which works fine with a PS2 adapter, but no PS2 port for a mouse. Every adapter I've tried hasn't worked for me, be it cable, SERIAL-PS2 adapter, dedicated serial card. The Data Technologies controller card that initially supported its serial mouse hasn't worked in 30 years afaik. I was looking at this thread as a potential solution.

ldeveraux wrote on 2026-06-18, 11:29:

I saw your thread and your adapter. My issue is I cannot get my serial port working with a mouse, so no Windows 3.1 for me. It has an AT keyboard port which works fine with a PS2 adapter, but no PS2 port for a mouse. Every adapter I've tried hasn't worked for me, be it cable, SERIAL-PS2 adapter, dedicated serial card. The Data Technologies controller card that initially supported its serial mouse hasn't worked in 30 years afaik. I was looking at this thread as a potential solution.

It sounds like your serial port isn't functional to begin with. In that case rio444's ISA card would solve the problem.

Mike_ wrote on 2026-06-18, 14:19:

ldeveraux wrote on 2026-06-18, 11:29:

I saw your thread and your adapter. My issue is I cannot get my serial port working with a mouse, so no Windows 3.1 for me. It has an AT keyboard port which works fine with a PS2 adapter, but no PS2 port for a mouse. Every adapter I've tried hasn't worked for me, be it cable, SERIAL-PS2 adapter, dedicated serial card. The Data Technologies controller card that initially supported its serial mouse hasn't worked in 30 years afaik. I was looking at this thread as a potential solution.

It sounds like your serial port isn't functional to begin with. In that case rio444's ISA card would solve the problem.

If you mean the physical port, I've tried replacing it (it's cabled, not part of the board). I've tried a completely newly made ISA serial card off Amazon it doesn't work either. I've tried a PS2 breakout cable on both cards and it doesn't work. I'm at wits end with this..

ldeveraux wrote on 2026-06-18, 17:16:

If you mean the physical port, I've tried replacing it (it's cabled, not part of the board). I've tried a completely newly made ISA serial card off Amazon it doesn't work either. I've tried a PS2 breakout cable on both cards and it doesn't work. I'm at wits end with this..

I mean port as in electronics on board rather than just the connector, which is unlikely to be damaged. But if another ISA serial card doesn't work, I have no idea. In that case even rio444's ISA card might not work.

But a PS/2 cable on serial header just isn't going to work no matter what. They are completely different, both electrically and in protocol.

Mike_ wrote on 2026-06-18, 17:33:

ldeveraux wrote on 2026-06-18, 17:16:

If you mean the physical port, I've tried replacing it (it's cabled, not part of the board). I've tried a completely newly made ISA serial card off Amazon it doesn't work either. I've tried a PS2 breakout cable on both cards and it doesn't work. I'm at wits end with this..

I mean port as in electronics on board rather than just the connector, which is unlikely to be damaged. But if another ISA serial card doesn't work, I have no idea. In that case even rio444's ISA card might not work.

But a PS/2 cable on serial header just isn't going to work no matter what. They are completely different, both electrically and in protocol.

I feel like I've taken over this thread with stuff that doesn't belong. But how does a PS2>serial adapter (like Logitech offers) work if they are incompatible?

ldeveraux wrote on 2026-06-18, 17:42:

I feel like I've taken over this thread with stuff that doesn't belong. But how does a PS2>serial adapter (like Logitech offers) work if they are incompatible?

A passive adapter works only if the mouse itself supports both serial and PS/2. Otherwise it won't work.

Active adapters like what we have been discussing here have a microcontroller that handles communication with PS/2 mouse and some other support chips. In case of a PS/2 to serial adapter there's a RS-232 transceiver for level shifting and in case of rio444's ISA card a CPLD chip handles communication with ISA bus if I have understood correctly.

Mike_ wrote on 2026-06-18, 18:25:

ldeveraux wrote on 2026-06-18, 17:42:

I feel like I've taken over this thread with stuff that doesn't belong. But how does a PS2>serial adapter (like Logitech offers) work if they are incompatible?

A passive adapter works only if the mouse itself supports both serial and PS/2. Otherwise it won't work.

Active adapters like what we have been discussing here have a microcontroller that handles communication with PS/2 mouse and some other support chips. In case of a PS/2 to serial adapter there's a RS-232 transceiver for level shifting and in case of rio444's ISA card a CPLD chip handles communication with ISA bus if I have understood correctly.

So... what now? I assume a Logi PS2 optical mouse supports serial? I don't care from serial, PS2, BUS, smoke signals, I would really like a mouse that works with a 486DX-S board with a seemingly malfunctioning serial port.

ldeveraux wrote on 2026-06-18, 20:36:

So... what now? I assume a Logi PS2 optical mouse supports serial? I don't care from serial, PS2, BUS, smoke signals, I would really like a mouse that works with a 486DX-S board with a seemingly malfunctioning serial port.

Most likely it doesn't, and that's causing your problem instead of there being anything wrong with serial port itself.

Mike_ wrote on 2026-06-18, 21:23:

ldeveraux wrote on 2026-06-18, 20:36:

So... what now? I assume a Logi PS2 optical mouse supports serial? I don't care from serial, PS2, BUS, smoke signals, I would really like a mouse that works with a 486DX-S board with a seemingly malfunctioning serial port.

Most likely it doesn't, and that's causing your problem instead of there being anything wrong with serial port itself.

I also have a new serial mouse (OP-500) that doesn't work either. It seems to be detected on the serial port with cutemouse, not detected in a DOS game. It works on my other PC with a working serial port.

ldeveraux wrote on 2026-06-18, 21:31:

I also have a new serial mouse (OP-500) that doesn't work either. It seems to be detected on the serial port with cutemouse, not detected in a DOS game. It works on my other PC with a working serial port.

I will note that through testing cutemouse with Mike's serial adapter, cutemouse can "detect" a mouse on serial even though one isn't connected or the serial port isn't working. So it's not much of an indication that anything is happening.

ldeveraux wrote on 2026-06-18, 21:31:

Mike_ wrote on 2026-06-18, 21:23:

ldeveraux wrote on 2026-06-18, 20:36:

So... what now? I assume a Logi PS2 optical mouse supports serial? I don't care from serial, PS2, BUS, smoke signals, I would really like a mouse that works with a 486DX-S board with a seemingly malfunctioning serial port.

Most likely it doesn't, and that's causing your problem instead of there being anything wrong with serial port itself.

I also have a new serial mouse (OP-500) that doesn't work either. It seems to be detected on the serial port with cutemouse, not detected in a DOS game. It works on my other PC with a working serial port.

If your serial port is on a ribbon cable breakout cable, it can be a pinout issue too. There are two pinouts "DTK/Intel" vs "AT/Everex" but it basically boils down to

12345
6789

vs.

13579
2468

You can use a multimeter and verify which pins connect with ground to compare the serial card vs. ribbon cable.

NeoG_ wrote on 2026-06-18, 23:51:

ldeveraux wrote on 2026-06-18, 21:31:

I also have a new serial mouse (OP-500) that doesn't work either. It seems to be detected on the serial port with cutemouse, not detected in a DOS game. It works on my other PC with a working serial port.

I will note that through testing cutemouse with Mike's serial adapter, cutemouse can "detect" a mouse on serial even though one isn't connected or the serial port isn't working. So it's not much of an indication that anything is happening.

If cute mouse reports "mouse systems mode" it's not actually detecting anything. Mouse systems mice didn't support any type of presence detection.

If it says microsoft or logitech mode, it's actually seeing something