Just DM me if you want the Kicad files and you can modify it however you wish

Paar wrote on 2022-03-28, 15:36:

How high is it? Will it interfere with an ISA card?

Some ISA cards have a cut-out in the PCB between the slot opening and the ISA connector. If possible, position all cards with the cut-out under the KBC. A month ago I produced two more of my version of this adapter (no PCB required). I'll see if they fit under the ISA card for the case that the ISA card does not have the cut-out.

maxtherabbit wrote on 2020-11-15, 19:57:

I sold some boards to a friend of mine who is using a Belkin Omniview and he is reporting that it will work only briefly and then stop

Did the 7406 variant of this adaptor solve your friend's issue when using a KVM?

feipoa wrote on 2022-03-28, 18:37:

Did the 7406 variant of this adaptor solve your friend's issue when using a KVM?

Dunno yet. Just sent him the gerbers last week. I'll report back if and when he builds one

feipoa wrote on 2022-03-28, 18:37:

Some ISA cards have a cut-out in the PCB between the slot opening and the ISA connector. If possible, position all cards with the cut-out under the KBC. A month ago I produced two more of my version of this adapter (no PCB required). I'll see if they fit under the ISA card for the case that the ISA card does not have the cut-out.

I'm very limited with ISA cards on my VLB board so small height of the adapter is crucial for me. Would be nice to know what you came up with.

I pulled out a motherboard with the KBC between the ISA slot and the board's slot edge and tried to fit ISA cards with and without the KBC mod.

Here I am showing a slotted ISA card (Mach64 graphics card). You will notice that there is ample space between the ISA card and the KBC mod's top surface,

However, with a non-slotted ISA card (Magic S23 sound card), I could not even begin to insert the card into the ISA slot,

Even without the KBC mod, the non-slotted sound card barely fits. If you look closely, you'll notice that the KBC chip prevents full insertion - there's a slight angle to it still,

So if you are unable to position your ISA cards out of the way of the KBC, and you are unable to use slotted ISA cards, then your only option is to perform the mod on the motherboard itself. Many motherboards contain a 7406 inverter IC for the keyboard controller and usually have two unused inverters on the 7406. You would use these unused inverter in/out pins on the 7406 for your PS/2 mouse modification. In the first few pages of this thread, I show an example of doing the mod on the motherboard directly.

If you are able to find slotted ISA cards, you will still need to confirm that maxtherabbit's PS/2 unit is short enough to fit. My first thought after viewing the rendering is that it is too tall still.

How many ISA card slots does your motherboard have and how many ISA cards do you want to install? Worst case is that the KBC socket covers 3 slots. Best case is it covers only 2. If you have six 16-bit ISA slots and one or two 8-bit slots, you should be able to work around this limitation. For the most part, you can use 16-bit sound cards in the 8-bit slots. You can also use 8-bit serial, parallel, and IDE cards. It may be that you don't need any slotted ISA cards, or you can get away with using just 1 slotted ISA card.

My board was never really intended for the motherboards that place the KBC on the rear edge tbh. I tried to make it as small as possible on general principles but I don't even own a motherboard with the KBC there to design around.

To be clear what I was proposing was to solder the KBC directly to the interposer board and solder the interposer board directly to the motherboard using the shortest available pin headers, no sockets anywhere in the stack. Paar's idea to relocate the 7406 and passives to the underside would probably make this more effective.

What is the seated height of your fully assembled unit? The seated height of my assembly is 7.5 mm.

The allowable distance, when using a non-slotted ISA card, from motherboard PCB to top of KBC is about 7.5 mm. This is the height of one DIP socket+one seated KBC. Assuming Paar's motherboard's KBC socket doesn't have any DIP components hiding under it, my PS/2 adapter assembly should work if he desolders his KBC DIP-40 socket.

KBC on my board (Chicony CH-471B) sits next to 3 of my ISA slots. It's even a little cramped in there, surrounded by other components, but I think it can be done with some custom solution. I like the PCB solution more as I don't want to have a wire mess on my board. I like it tidy 😀.

I'll probably put all components on the bottom side of the PCB, solder the board directly to the mainboard and then solder the KBC to the board if necessary. Maybe use right angle pins for the mouse cable.

the ticket to making it as thin as possible would probably be to move the resistors, caps, and inverter to the underside and place the inductors next to the mouse header

then you could make it as thin as the PCB itself (1.6mm) + the insulation height on the shortest pin headers available (~1.5mm) + the KBC itself

I've been struggling to get and optical mouse working on my 286 without an externally powered dongle, and with Rio's situation, I can't just buy another ISA PS2 card, so I'm wondering if this would with with my 286?
It's a DTK motherboard (PTM-1636c) with the PC Chips F82C235 chipset.
I found the interposer on oshpark and then found this thread.

Does the BIOS need to support PS2 mice, or can I just swap the keyboard controller?
If it does need BIOS support, is there a generic bios that supports that chipset for this, like AMI or Mr.BIOS?

You can also use a Protocol Translater.
https://www.serdashop.com/PS2TOSERIAL
If you want you can also build it yourself, files are on my github.

Yes the BIOS and the Keyboard Controller need to support it.
Maybe a Driver could also work without BIOS Support.

matze79 wrote on 2022-06-20, 22:28:

You can also use a Protocol Translater. https://www.serdashop.com/PS2TOSERIAL If you want you can also build it yourself, files […]
Show full quote

You can also use a Protocol Translater.
https://www.serdashop.com/PS2TOSERIAL
If you want you can also build it yourself, files are on my github.

Yes the BIOS and the Keyboard Controller need to support it.
Maybe a Driver could also work without BIOS Support.

yes, I bought one, it requires external power, which I can't provide easily due to having too many things plugged in and not enough plugs, and rather than implement an internal solution that is much more complicated, an interposer seems much easier and more elegant solution for my setup for me because the keyboard controller is already socketed and away from the ISA slots.

DNSDies wrote on 2022-06-20, 22:25:

I've been struggling to get and optical mouse working on my 286 without an externally powered dongle, and with Rio's situation, […]
Show full quote

I've been struggling to get and optical mouse working on my 286 without an externally powered dongle, and with Rio's situation, I can't just buy another ISA PS2 card, so I'm wondering if this would with with my 286?
It's a DTK motherboard (PTM-1636c) with the PC Chips F82C235 chipset.
I found the interposer on oshpark and then found this thread.

Does the BIOS need to support PS2 mice, or can I just swap the keyboard controller?
If it does need BIOS support, is there a generic bios that supports that chipset for this, like AMI or Mr.BIOS?

I'll let maxtherabbit, feipoa, etc. speak but I don't believe the hardware side is as simple as a drop-in replacement for the KBC. There are wires you need to run to connect the KBC to IRQ 12, and so forth.

BIOS support is required. For AMI Color BIOS in particular, the PS/2 mouse support is already there, just disabled when the BIOS image was built. As no one has AMIBCP, it's possible to use a hex editor to flip the PS/2 mouse support on and then bypass the checksum verification (or guess which byte is the checksum and recalculate it). I don't have an easy HOWTO of this process written up yet. And on a 286, it's likely your BIOS is too old anyway.

If you know assembly, you can determine whether your BIOS might have PS/2 mouse support by using DEBUG to generate an INT 15 with AX=0C200h (http://www.ctyme.com/intr/rb-1596.htm) and trace through the BIOS code and see if it ever checks whether AH=0C2h. If so, that's PS/2 mouse support. If it's like the AMI Color I mentioned above, the PS/2 mouse functionality is also gated by a TEST CS:[....],xxh instruction which blocks the PS/2 mouse support if a bit in the BIOS is not set.

matze79 wrote on 2022-06-20, 22:28:

Yes the BIOS and the Keyboard Controller need to support it.
Maybe a Driver could also work without BIOS Support.

Ah yes, this is true. In particular without the AMIBIOS modification I believe feipoa had a modified NTDETECT.COM and such to detect a PS/2 mouse even though the BIOS claims there isn't one. But you would have to have this hack for each platform (DOS, Windows, etc.) where you want to use a PS/2 mouse despite the lacking BIOS support.

The generic MR BIOS for 286 supports PS/2. Rio444 already posted a DOS TSR that adds PS/2 support to DOS even without BIOS support in this very thread

Thanks, the osh park PCB I ordered is the older one with discreet transistors, and the only external wiring to it seems to be for IRQ 12 and of course to a PS2 female plug. I should be able to handle that no problem, I can just grab it from the first ISA slot.
I'm going to try the MR BIOS for this, as the bios that comes with this motherboard is horrible to use. If it doesn't work, I can try the TSR.

Still wondering how to create the adapter so it would fit next to ISA slots (without blocking any cards). Did some research if there are some keyboard controllers in SMD form factor and there are.

The first is VIA VT82C42V in PLCC44 form factor (datasheet)
Still too big/high for my use case.

The second is VIA VT82C416 in QFP-128 form factor (online shop). This would probably be the best bet but unfortunately I cannot find any pinout for this chip, only information that it has VT82C42 controller integrated.

Maybe there are other chips but haven't found any yet. Ideally some in SOP form factor.

EDIT: Found datasheet for the VT82C416, has been buried in a larger document. It looks incompatible though with the older keyboard controllers.

VT82C416 contains internals of 82c206 (rtc/dma/irq) and more (Clock Generator, isa buffers)

you could design modern replacement using RP2040 (with resistor ladder instead of translating buffers o make it super cheap)

Could be nice project, but out of my league. Let's hope it will happen sometime in the future. It's probably the only way how to do it properly while not looking messy.

the cross section of boards that cannot be used with my existing design and that do not have ps/2 support already is pretty small, so I decided to ignore them

I'd suggest you do the same 😀

"block any ISA cards" is also relative, if you use an ISA card without the stupid lip at the rear of the edge connector there is generally no problem