If the motherboard uses a 40-pin keyboard controller chip, it can be modified for PS/2 mouse support.

I think chip density acceptance is a BIOS and/or chipset (northbridge) thing. I have been able to use the BIOS for the 4DPS on some SiS 496-based boards to get support for higher memory densities, but the PCI routing table needs to be altered as well.

To Feipoa.
It is a little off topic but I bought this mainboard P4U880A/IO V1.0(S1.2). See the picture. You wrote me that if there is AMIKEY chip onboard that there is possible a PS/2 mod. I am planning to desolder the AMIKEY chip and rise this chip on the DIP socket like this and use this USB to PS/2 bracket from Delock. Could you tell me what wire and to where to connect? I want to connect both keyboard and mouse to PS/2.
I bought this motherboard with 1024kB cache and the TAG is only 256kB as is on the picture. The board after start showes only 256Kb of chache. I think that I need to get the TAG with 512kB. Am I right?
Thanks.

You should probably read this thread for pin connections, Native PS/2 mouse implementation for 386/486 boards using the keyboard controller

For keyboard DIN to mini-DIN, there's a table of pins here, http://www.instructables.com/id/Old-Keyboard- … -PS2-converter/

Yes, the TAG for 1024K cache is usually 64kx8, which is DIP-32 with "512" written on the top. Jumpers must be set accordingly though. If the motherboard doesn't support 1024K, you'll need to do some soldering for TAG A16, and maybe others.

Any reason you want to use machine pin DIP-40 sockets? The make ends of your KBC aren't round, are they?

I'm not sure about modifying a Phoenix BIOS for PS/2 mouse support. Its possible that it is already built-in. Alternately, perhaps the TSR program provided in the first noted thread will work.

The 1024K of cache works for me. This motherboard has this BIOS UMC 8880A PCI/ISA PnP Ver.2.1 Oct. 30, 95/ PhoenixBIOS Version 4.04 and supports 256MB of EDO ram. If someone has a newer BIOS please let me know. I tried some PS/2 mod but it does not work yet. There is an item PS/2 mouse support On/Off in BIOS. A question is if it works.
I soldered an additional socket for removing and rising of the AMIKEY-2 chip. I took GND (black wire of bigger diameter) and +5V (red wire of bigger diameter) from bottom part of a keyboard DIN connector and connected them to DELOCK PCB (rear bracket USB --> 2x PS/2) with PS/2 connectors. I connected KB clock (pin number 1 - white wire) and KB data (pin number 27 - green wire) and MOUSE clock (pin number 39 - black wire) and MOUSE data (pin number 28 - red wire) to risen socket for AMIKEY-2 and connected them to DELOCK PCB. When I turn on the motherboard it writes Keyboard error. On the motherboard there is presented 7406N inverter chip so I according to my experiences it should be work but with settings of a few jumpers which are missing the same like on Chaintech 486 SPM. I received on 486SMP a message kezboard error but after rejupming of some jumpers it works. According to the manual there are jumpers J22, J31 and J32 anad some of these must be reconnected by jumpers. Do you know which one please? Or what does mean External KC? Does it mean that caring about PS/2 features is not responsible UM8886 chip or AMIKEY-2? I am not 100% sure if I am doing the things correctly I am not an electrician. Please help me with that. Thank you.

Without the board in front of my face, there isn't much I can do to help. You could try ordering some of the KBC-based ps/2 mouse adapters from OSHPark. Re: Native PS/2 mouse implementation for 386/486 boards using the keyboard controller . The link is in that thread somewhere.

I soldered all headers for jumpers J1, J2, J3 J22, J31 and J32. All of these were set in default to External KC by soldered wires. I set them to Internal KC and Keyboard and mouse do not work again. When I put the keyboard connector back to DIN connector the keyboard works. I ordered PCBs for PS/2 mouse support from OSHPark and I let you know then if it will work.
I have another problem with this motherboard. My WD Raptor 36GB is not recognized correctly by this motherboard. See the pictures. I added an option about the PS/2 mouse support. It only writes Starting MS-DOS ant that's all. It is about BIOS settings or BIOS support for larger HDDs? This HDD works perfect on Chaintech 486 SPM, Soyo 4SAW2 and on Biostar MB-8433 without issues. Does have someone a newer BIOS for P4U880A/IO? It seems that maybe should work a BIOS from Elitegroup UM8810PAIO.

Soldering on the jumper headers may not be enough. For the PS/2 mouse, did you ensure that the PS/2 mouse capacitors, resistors, and inductors are used on this motherboard? There may be empty solder pads or vias for these components. It could also be that there aren't any sold pads or vias for this components, in which case, you'll need to add them. You also need to ensure that the inverter IC is wired correctly for PS/2 mouse support.

I sorta remember someone adding the UM8810PAIO BIOSes on this forum. You'll have to search for them. I recall someone got their PS/2 mouse working on that board.

The PS/2 mouse works on UM8810PAIO rev 2.0 and 2.1. These have PS/2 header. See this link. I made my PS/2 mod the same like that guy.
http://www.dosforum.de/viewtopic.php?f=1&t=10 … 0eaf208835c56ee
I will check the motherboard carefully if there are empty spots but it seems that there are none.

To Feipoa
A user colpoz from Vogons sent me a newer BIOS UMC 8880A PCI-ISA PnP BIOS Ver.2.3 Jan. 4, 96. I tried the PS/2 mod on this motherboard as on dosforum's link and pictures above and PS/2 keyboard and PS/2 mouse does not work.
I tried the PS/2 MOD from Rio444 with PCB from OSHPark and when I loaded ps2suppc (both older and newer version) the system freezed and this MOD blocks integrated IDE controller on the motherboard. I had to use the external PCI controller for the tests. I tried this motherboard with your BIOS v2014 for MB-8433 and when I loaded ps2suppc (both older and newer version) and than the cutemouse driver a mouse cursor appeared and the system freezed.
Could you check the attached BIOS and tried to modify it for PS/2 support? Thanks.

I cannot modify Phoenix BIOSes.

You need to develop a firmer understanding of how the motherboard is wired and what changes are needed to the KBC to use a ps/2 mouse. There is a circuit diagram provided by RIO444 and me in the other thread.

You may also want to provide a high-resolution photo of various angles of the OSHPark PCB mod you soldered. The OSHPark PCB didn't work for me. I suspect it may be due to PCB thickness, but I do not know for sure. I provided a diagram in the other thread for how I wired up my own version of the PS/2 mouse adapter. Perhaps you can try that approach. Even when I made the second adapter, I got confused over the wiring. It is a little hard to wrap your head around the two pins which are being intercepted. However, I think the write-up I did for Keropi is pretty clear. Keep in mind, there is no guarantee this will work. I have only tried it on 386 motherboards.