My board uses a simple LC filter with the 470uH/47pF giving a ~1MHz cutoff. This isn't a part of the design that a ton of thought went into admittedly, but it seems to work well so I stuck with it

deltapi wrote on 2024-02-08, 03:57:

maxtherabbit wrote on 2024-02-05, 17:33:

If you're in the USA I'd be happy to give you a board, if not I would just want shipping reimbursement.

I'm in Canada, but I'd gladly pay shipping expenses, thank you!

Are you able to send and receive DMs? Send me your shipping address for a quote please

maxtherabbit wrote on 2024-02-08, 18:38:

My board uses a simple LC filter with the 470uH/47pF giving a ~1MHz cutoff. This isn't a part of the design that a ton of thought went into admittedly, but it seems to work well so I stuck with it

It works for me too 😀 I used your project and can report success with Soyo SY-025N2 (after modifying BIOS with Modbin).
Thank you very much!
I was just curious because I never found any values for these ferrite beads.

feipoa wrote on 2024-02-08, 08:35:

I noticed that the Lucky Star LS-486E rev.D upgrade guide uses 470 uH, which I assume maxtherabbit adopted. It was not clear to me why this value was selected. Is there any benefit in using the higher inductance?

If you take a look at datasheet on VT82C42N/HT6542B you'll see the keyboard and mouse schematics are identical and both don't include inductors.
Both Zida 4DPS and LuckyStar LS-486e have 470uH inductors in series with KBD_CLK and KBD_DATA. But only LS-486e has footprints for inductors in series with MS_CLK and MS_DATA. So I decided to peek values from keyboard circuit 'cause they share the same protocol.

froller wrote on 2024-02-09, 13:50:

feipoa wrote on 2024-02-08, 08:35:

I noticed that the Lucky Star LS-486E rev.D upgrade guide uses 470 uH, which I assume maxtherabbit adopted. It was not clear to me why this value was selected. Is there any benefit in using the higher inductance?

If you take a look at datasheet on VT82C42N/HT6542B you'll see the keyboard and mouse schematics are identical and both don't include inductors.
Both Zida 4DPS and LuckyStar LS-486e have 470uH inductors in series with KBD_CLK and KBD_DATA. But only LS-486e has footprints for inductors in series with MS_CLK and MS_DATA. So I decided to peek values from keyboard circuit 'cause they share the same protocol.

Interesting. For the boards I measured the 2-10 uH values for mouse clock and data, it would be interesting to see what these boards are using for keyboard clock and data. I think they were of the same range. Nonetheless, it doesn't seem like the value here matters all that much. When I produce the first prototype of this adaptor, I didn't even use the inductors, so 0 uH (not including trace inductance).

Those parts only exist there for EMC regulations, they don't serve a functional purpose so to speak.

feipoa wrote on 2024-02-09, 15:30:

Interesting. For the boards I measured the 2-10 uH values for mouse clock and data, it would be interesting to see what these boards are using for keyboard clock and data. I think they were of the same range. Nonetheless, it doesn't seem like the value here matters all that much. When I produce the first prototype of this adaptor, I didn't even use the inductors, so 0 uH (not including trace inductance).

VT82C42N datasheet says the clock is generated by the device (kbd or mouse) and lower limit is 250kHz (max 2ms pulse on clock line). No upper limit mentioned.
470uH with 4.7kOhm pull-up resistors gonna be ok up to 1.5MHz.
I use 470uH and optical mouse from mid 2000's works perfectly for at least a year. However lowering this inductance seems do no harm as some motherboards don't use them at all.

Tiido wrote on 2024-02-09, 15:52:

Those parts only exist there for EMC regulations, they don't serve a functional purpose so to speak.

seems true

maxtherabbit wrote on 2024-02-08, 20:01:

Are you able to send and receive DMs? Send me your shipping address for a quote please

I can't yet, but I will do so once I can.

I've started a different thread about this, but has anyone here been able to enable PS2 support on motherboards with UMC UM8498F/UM8496F chipset? I'm trying to reverse engineer this on my Octek Hippo 10. This board is interesting as it has solder points for PS2 connectors (KB and mouse), but it appears they're wired for external keyboard controller only. The UM8498F has a keyboard controller integrated (not UM8496F interestingly) and it has to be disabled before PS2 connectors can be used. Unfortunately as there's no datasheet for this chipset it's somewhat hard guess what to do exactly.

I've been using the HOT-433 PS2 mod as a guide but for the UM8498F chipset it's not entirely the same. For starters, it seems that the multifunction pin which functions as CS enable for KB/BIOS ROM and for enabling/disabling internal keyboard controller on UM8881 works only as a CS enable signal on UM8498F. I may be wrong it it seems that way on my board as that pin is not connected to anything else.

I have been able to locate two zero ohm resistors which change the routing from UM8498F to pins of external controller.

1UM8498 pin	resistor no.				purpose
2167			R71/R72						KBC pin 39 (KB data input)/CPU RESET pin output (in the CPU socket)
3166			R61/R62						KBC pin 1 (KB clock input)/KBC pin 3 (KB controller clock output)
4165			fixed (no resistor)			KBC pin 6 (CS enable) and BIOS ROM (CS enable)
5115			R120/R121					pull-up for enabling internal KBC, pull-down for disabling it

Keylock is wired both to a southbridge and pin 34 on KBC. Connection between keylock pin and sountbridge can be severed with jumper JP4.

That is as far as I could get so far, for more progress I have to get my hands on a motherboard with this chipset which has a jumper for enabling/disabling internal keyboard controller. There are several models I know of:

ECS UM4980
ECS UA4982
Pine Technology PT-430
Aquarius Systems/BCOM MB-4DUVC

Paar wrote on 2024-02-29, 17:45:

Aquarius Systems/BCOM MB-4DUVC

There was a batch of "Techmedia" motherboards on eBay last year that I think are the same as that one. Onboard everything (VLB IDE, VLB VGA, IO, etc.)

I have it put away now but there are likely a bunch here or on the retro web discord who got one. I do remember it has the position on it for a PS/2 mouse, but I haven't made any attempt to add one.

Offtopic:

But I recently learned, from reading the datsheet, that VIA's keyboard controller is 100% implemented with logic gates and is not a programmed microcontroller like the other Intel 8042 clones. VIA claims it's faster because of this, but I'm a bit dubious if that really matters or not.

jakethompson1 wrote on 2024-03-01, 03:25:

There was a batch of "Techmedia" motherboards on eBay last year that I think are the same as that one. Onboard everything (VLB IDE, VLB VGA, IO, etc.)

I have it put away now but there are likely a bunch here or on the retro web discord who got one. I do remember it has the position on it for a PS/2 mouse, but I haven't made any attempt to add one.

Thanks for the tip, I'll try to find help on the RetroWeb Discord channel too.

I've noticed something weird going on. Most (if not all) motherboards with this chipset don't have any 7406 inverted between the external KBC and connectors. I have read that internal keyboard controller in the UMC chipset can drive keyboard/mouse cable no problem but when using external one you have to buff the signal through an inverter. Even the motherboards that I mentioned with the ability to disable the internal controller don't have one, not even an unpopulated place where one can be soldered. What is going on here?

Paar wrote on 2024-03-01, 08:06:

Even the motherboards that I mentioned with the ability to disable the internal controller don't have one, not even an unpopulated place where one can be soldered. What is going on here?

Are you saying that they DO have a unpopulated DIP-40 footprint for a KBC but DO NOT have a footprint for the 7406?

Alright, some of them have 74LS244 footprint prepared, but a lot of them don't have anything, as for example my Octek Hippo 10. Even ECS UM4981 AIO which has external keyboard controller from the factory, doesn't have any inverter soldered in. Perhaps they were counting with peripherals which have these buffers integrated?

Shouldn't be problem though, I can create an adapter board which includes such inverter, similar to the adapter board with PS2 mouse support.

Paar wrote on 2024-02-29, 17:45:

I've started a different thread about this, but has anyone here been able to enable PS2 support on motherboards with UMC UM8498F/UM8496F chipset?

No! - I have the same issue. I also replied in your thread... I do really want to get it working with that board. I like it since it has an external VRM.

Paar wrote on 2024-03-01, 15:54:

Shouldn't be problem though, I can create an adapter board which includes such inverter, similar to the adapter board with PS2 mouse support.

I'd be very happy to test with your adapter on my board.

Well I want to define what pin does what and what needs to be connected where. It's quite possible different motherboard will need different approach but when I have all figured out I can assist you with making a functional adapter for your board.

I think I have it mostly figured out, with that I have updated the pinout table in the earlier post. I'm touch with a user from retro web Discord channel which will measure UMC pins on his board. When it's confirmed, I'll do the mod and we'll see what happens.

I have some news about my project. With a help of member of retro web Discord channel, I've been able to disable internal keyboard controller and enable external one. So the keyboard works great with external KBC, unfortunately once I connect PS2 mouse, the keyboard stops responding right after POST screen (it works OK before that). As Octek Hippo 10 has solder footprints for PS2 connectors for keyboard and mouse, and keyboard works great when mouse is not connected, I assume I have something wired wrong. More research is to be done.

Paar wrote on 2024-03-06, 17:43:

I have some news about my project. With a help of member of retro web Discord channel, I've been able to disable internal keyboard controller and enable external one. So the keyboard works great with external KBC, unfortunately once I connect PS2 mouse, the keyboard stops responding right after POST screen (it works OK before that). As Octek Hippo 10 has solder footprints for PS2 connectors for keyboard and mouse, and keyboard works great when mouse is not connected, I assume I have something wired wrong. More research is to be done.

Try not to touch/move mouse while system is booting.
If system freezes (or KB stops working) at the moment you move the mouse it indicates you have some issues with mouse interrupt (IRQ12).
Similar problem I had with transplanted VT82C42 KBC while IRQ12 routing jumper was incorrectly set.

UPD make sure no device other than KBC uses IRQ12