Unfortunately, after booting the M919, the system hangs on:

1CMOS system options not set
2CMOS display type mismatch
3
4RUN SETUP UTILITY
5Press F1 to RESUME.

If I press F1, nothing happens. The boot process just stops here.

I decided to put the original BIOS back into the motherboard and see if PS2SUPPC.COM would enable my mouse via a TSR, but it did not. PS2SUPPC is a small app by Rio444 that we previously used to enable PS/2 support before it was discovered how to modify AMI BIOSes (pre-WIN BIOSes).

I'm attaching the original M919 05/06/96 BIOS, along with my PS/2 moddified BIOS. Also included in the archive is the original 9190506 BIOS which has been decompressed with amideco. I'm hoping someone knows how to get PS/2 working on the M919. I suspect there is some PS/2 mouse code missing from the BIOS.

Perhaps there is a strap on the southbridge to enable/disable the mouse at a hardware level? My assumption would be that if PS2SUPPC can't enable it there is a hardware problem, as that utility doesnt rely on BIOS code whatsoever as far as I know.

One other thought - are you certain the pin header you used for the mouse connector was fully floating before you connected the magnet wire? What if they routed it to something else that is pulling your clock and data lines up or down

maxtherabbit wrote on 2026-07-31, 17:07:

Perhaps there is a strap on the southbridge to enable/disable the mouse at a hardware level?

That's possible, though I suspect this is done via the BIOS. Some notes from the unofficial UM8886 chipset documentation:

1The BF variant [of the UM8886] can remap the pin usage for PS/2 mouse (shared with ISA bus address signals).  
2
3[Refering to the IBC registers]
440.10 
5Set on B2 revision, but cleared if no PS/2 mouse
6
743.0F 
8INTB target IRQ. NOTICE resulting IRQ may collide if incorrectly shared (PS/2 mouse + PCI) probably level vs edge triggered
9
1045.01 
11Set on B2 revision, but cleared if no PS/2 mouse

maxtherabbit wrote on 2026-07-31, 17:07:

One other thought - are you certain the pin header you used for the mouse connector was fully floating before you connected the magnet wire? What if they routed it to something else that is pulling your clock and data lines up or down

I did not probe every via on the motherboard, but was relying primary on trace optics. Here's photos of the J2 header. It should be pretty obvious which traces I cut (there's 3). Plus, I had to bridge a spot that was trace in/trace out.

If you use a PCI VGA card you can use a Biostar MB8433 BIOS on the M919 and test if the PS2 mouse works. If it does work it points to a software problem, if it doesn't it points to a hardware problem.

A VLB VGA card didn't work for me and the combination of MB8433 BIOS on a M919 with a ISA VGA didn't want to boot of my ISA combo DiskOnChip/USB card. No L2 cache was installed during my tests.

That's a pretty good idea to test it connectivity. I'll try this the next time I have a testbed setup.

maxtherabbit wrote on 2026-07-31, 17:07:

Perhaps there is a strap on the southbridge to enable/disable the mouse at a hardware level? My assumption would be that if PS2SUPPC can't enable it there is a hardware problem, as that utility doesnt rely on BIOS code whatsoever as far as I know.

One other thought - are you certain the pin header you used for the mouse connector was fully floating before you connected the magnet wire? What if they routed it to something else that is pulling your clock and data lines up or down

On that connector, it seems that pin 1 goes to pin 95 of the SIO and pin 3 goes to pin 75 (FDC_WGATE?) along with a connection to a resistor pack by the SIMM slots. I wonder if it's for some manufacturing test connector?

I'm also very interested in this modification possibly. Looking at the MB-8433UD and reading through mkarcher's post about it: Success: Adding a PS/2 mouse port to the Shuttle HOT433 (using a dedicated keyboard controller chip)
which suggests that the MB-8433UUD has a resistor network used as a switch at the manufacturing level to select between PS/2 and non-PS/2 mouse models, that disconnects the ISA signals the mouse port shares with when not installed, allowing the mouse to work.

Can you check where the LA17, 18, 19 pins on the ISA connector route to? I think they go to the unpopulated RN17 on the 8433. If it does, it may be worth seeing if the M919 can unhook those pins in an easy way or if that'll require cutting the traces...

Thermalwrong wrote on 2026-08-05, 03:19:

Can you check where the LA17, 18, 19 pins on the ISA connector route to? I think they go to the unpopulated RN17 on the 8433. If it does, it may be worth seeing if the M919 can unhook those pins in an easy way or if that'll require cutting the traces...

bro what

maxtherabbit wrote on 2026-08-05, 12:56:

Thermalwrong wrote on 2026-08-05, 03:19:

Can you check where the LA17, 18, 19 pins on the ISA connector route to? I think they go to the unpopulated RN17 on the 8433. If it does, it may be worth seeing if the M919 can unhook those pins in an easy way or if that'll require cutting the traces...

bro what

Sorry, it was late and I really wanted to finish up the post. I have an M919 but no Biostar MB-8433UUD board to check, I can only refer to pictures online.
I should have included the quote from mkarcher in that other thread, where he's done some reverse engineering of how the mouse is implemented on the MB-8433UUD. Because I knew I'd seen some reference to this information before but it's not referred to in this current thread.

mkarcher wrote:

Integrated mouse port While this post is not about the integrated PS/2 interface, I also reverse engineered something about the […]
Show full quote

Integrated mouse port
While this post is not about the integrated PS/2 interface, I also reverse engineered something about the PS/2 port. I will write down the results in this paragraph, but you can skip until the next heading for the main point of this post.

The PS/2 mouse interface is multiplexed on pins used for the "ISA unlatched high address lines". These address lines are introduced with the 16-bit ISA extension of the IBM AT and present the address for the next cycle quite early (possibly even when the previous cycle is just about to be finished), and are not necessarily valid over the whole bus cycle. The primary purpose of LA17-LA19 is allowing 16-bit ISA plugin cards to signal their capability of handling a 16-bit cycle. This is used by 16-bit VGA cards for video memory access if they detect LA17-LA19 having the pattern 1,0,1 (which translates to the address range A000:0 to B000:FFFF). To allow zero-waitstate 16 bit memory writes, the MEMCS16 and 0WS pins need to be driven before the old-fashioned SA17-SA19 lines are guaranteed to be valid. The high address lines (to extend ISA from 1MB to 16MB address range) are also only presented as unlatched lines LA20 to LA23, and they need to be decoded by cards responding to past-1MB writes. The following pins change their function depending on enabling the internal PS/2 port:

Pin nr Mouse port on Mouse port off
198 unknown LA19
199 Mouse Data LA18
200 Mouse Clock LA17

On the Biostar 8433UUD board, which uses the integrated mouse port of the UM8886 south bridge, the connections of pin 198 to 200 can be reassigned to either the ISA LAx pins or the mouse port pins by moving a soldered resistor network (of the 4*0Ohm type). The specific 8433UUD I have at hand obviously has the resistor network soldered at the position that connects these pins to the PS/2 mouse port. The ISA pins LA17 to LA19 are driven from SA17 to SA19 instead. My guess it that this reduces ISA compatibility with 16-bit cards, because you can not drive LA17-LA19 and SA17-SA19 from the same pin without violating some ISA timing specification, but I did not yet get around to do thorough ISA tests (like testing 0WS ET4000 ISA graphics cards) on the UMC board.

Since those pins are shared with the mouse port on the southbridge, I think that if RN17 is populated then the mouse port would not be populated, but I've not found pictures of one without a mouse port.
From what I can see, achieving the same on the M919 is going to require cutting traces on the back and running the PS/2 mouse wires on the back instead. I may try that pretty soon once I trace out where pins 198, 199 and 200 go on the back.

Oh wow that's an odd choice for multiplexing but now I'm tracking

Thanks for the replies. I'm on summer holiday mode and often out of town. I probably won't get to this in a timely manner, but it is on the top of my list.

My understanding thus far is:
If there is not a resistor or resistor network to pull, it sounds like I'll need to cut traces from UM8886BF leading to ISA pins LA17/18/19. The drawback is reduced ISA VGA functionality? This is not a problem. I may also need determine where UM8886 pin 198 goes on the UUD board and replicate this route onto the M919 board?

Well, since those pins won't have any connection if there's no ISA cards present, trying that first would be easiest.
I've got to pull the M919 back out and have a go with your bios 😀

When I ran my previous tests, there was no ISA card connected - just a PCI VGA card.

I think there was also an AWARD BIOS for this board, named 2A4X5000. This can be PS/2-enabled with MODBIN.

I was able to find some time between summer canoe trips to trace out the aforementioned pins on the Biostar MB-8433UUD vs. PC Chips M919.

On the M919 motherboard, ISA pins:
ISA C5/LA19/Address 20 -----> UM8886BF pin 197 and 1K pull-up to 5V via RA15
ISA C6/LA18/Address 19 -----> UM8886BF pin 169 and 1K pull-up to 5V via RA15
ISA C7/LA17/Address 18 -----> UM8886BF pin 172 and 1K pull-up to 5V via RA15
UM8886BF pin 198, 199, 200 go no where that I can find.

On the UUD motherboard, ISA pins:
ISA C5/LA19/Address 20 -----> UM8886BF pin 197 (no pull-up)
ISA C6/LA18/Address 19 -----> UM8886BF pin 169 and 10K pull-up to 5V via RP6
ISA C7/LA17/Address 18 -----> UM8886BF pin 172 and 10K pull-up to 5V via RP6
UM8886BF pin 198 goes to an unpopulated via at RN17, hence, also goes nowhere.

I assume the path forward would be to de-solder RA15 on the M919 to break the pull-up connection at LA19.

I copied the UUD's traces for ISA LA19 onto the M919. To do this, I de-soldered RA15, bent up the appropriate pin on RA15, added some kapton tape to the via, then re-soldered RA15 (slightly elevated). This disconnects ISA pin LA19 from the pull-up. Unfortunately, I am still unable to use the PS/2 mouse on the M919 with the PS/2-edited 05/05/1996 WINBIOS.

Next, I tried the UUD BIOS on the M919. The PS/2 mouse worked fine. Next I tried the 2A4X5000 AWARD BIOS for the M919. It didn't have PS/2 support, but when loading PS2SUPPC, I am able to use the PS/2 mouse. I then edited the 2A4X5000 BIOS in modbin to enable PS/2 mouse support. PS/2 works now works fine on the 2A4X5000 w/out PS2SUPPC. I don't know the origin of the 2A4X5000 BIOS, or if it was even written specifically for the M919. I have attached it herein, along with the PS/2 mod.

Ideally, we'd want to use the PC CHIPS WINBIOS; I recall it being best with fast timings and overclocking. Do I need to disconnect LA17 & LA18 from the pull-up to get the original PC Chips WINBIOS working? Any idea on what to alter within the WINBIOS code?

pc2005's 8881/8886 datasheet suggests two bits on the 8886 are set if there is a PS/2 mouse and cleared if there is not.
I don't know if he means, always set if the board has the PS/2 port wired up even if no mouse is connected, or only set when a mouse is connected.
It's known that the 8886B does not always pass detection routines (such as that in the Linux kernel) checking whether the system has a PS/2 mouse port. So it's possible that is an issue too.

Are you familiar with how to use DEBUG to determine if IBC registers 40.10 and 45.01 are enabled? These are the registers noted in PC2005's datasheet.

I played around some with the UUD and the alternate M919 AWARD BIOS to see if I could get VLB working. Some VLB cards will boot to DOS, but there are artefacts on the screen. This negates the usefulness of these AWARD BIOSes if you want to run VLB. Part of the attraction to the M919 is the VLB slot.

I cleared the CMOS and put the original non-PS2 M919 BIOS back onto the motherboard. I booted into the BIOS to set the appropriate settings, then restarted. Keyboard works, but PS/2 mouse does not, even with PS2SUPPC. I then insert the PS/2 modified 919 BIOS. Now that I don't get the CMOS error, I am able to boot with a DOS floppy. Once at the command prompt, keyboard won't work. Next I boot to from a CF card on the IDE port, and am presented with an error:

1Internal Error in empty_8042: 8042 input buffer full. PAGE FAULT...

I'm not sure if this helps any, but the screenshot is attached below.

feipoa wrote on 2026-08-23, 02:52:

Are you familiar with how to use DEBUG to determine if IBC registers 40.10 and 45.01 are enabled? These are the registers noted in PC2005's datasheet.

You can use the pci.exe utility from mkarcher. I believe it would be pci 1060:886a 40 and pci 1060:886a 45