Might be of interest in this thread--

http://66.113.161.23/~mR_Slug/chipset/c ... =8735#8735

1**HT11          Single 286 AT Chip [no datasheet]               <Aug90...
2**HT12/+/A      Single 286 AT Chip with EMS support            c:Aug90...
3**HT18          80386SX Single Chip                            c:Sep91...
4**HT21          386SX/286 Single Chip (20 MHz)                 c:Aug91...
5**HT22          386SX/286 Single Chip (25 MHz)                 c:Sep91

I did'n t know about the HT21/HT22. How's overclockability with the HT22?

feipoa wrote on 2024-12-18, 22:00:

I did'n t know about the HT21/HT22. How's overclockability with the HT22?

Still looking for a board with that chip. 🙁

https://www.dosdays.co.uk/topics/Manufacturers/headland.php

HT22

A 286 and 386SX chipset launched in September 1991. For 286-class motherboards, the HT22 supports the Harris 80C286-25 MHz CPU.

It is likely the HT22 was a mildly upgraded HT21 that was able to cope with 25 MHz CPUs over the HT21's 20 MHz.

Could it be that it was rebranded for PCChips and thus have another name?
TRW yields nothing.

Nexxen wrote on 2024-12-19, 14:22:

Could it be that it was rebranded for PCChips and thus have another name?
TRW yields nothing.

I think TRW & Dosdays list of Headland chipsets are both based on the data in MR_Slugs list.
When you go that far back before the web, sometimes the oral tradition preserved in BBS's like MR_Slugs list are all you got.

I can search through some old PC mags and Computer shoppers later to see if they have anything.

douglar wrote on 2024-12-19, 15:26:

I think TRW & Dosdays list of Headland chipsets are both based on the data in MR_Slugs list. When you go that far back before […]
Show full quote

Nexxen wrote on 2024-12-19, 14:22:

Could it be that it was rebranded for PCChips and thus have another name?
TRW yields nothing.

I think TRW & Dosdays list of Headland chipsets are both based on the data in MR_Slugs list.
When you go that far back before the web, sometimes the oral tradition preserved in BBS's like MR_Slugs list are all you got.

I can search through some old PC mags and Computer shoppers later to see if they have anything.

This is a huge side quest for a fistful of XP points.
Thank you for your commitment.

Nexxen wrote on 2024-12-19, 16:49:

This is a huge side quest for a fistful of XP points.
Thank you for your commitment.

Looks HT-22 & HT18 use the same BIOS, but it is a different than the HT12
https://www.google.com/books/edition/The_Bios … nd+ht22&pg=PA28

Looks like HT-22 does 25Mhz FSB with 12.5 Mhz ISA
https://theretroweb.com/chip/documentation/ht … 0f014663141.pdf

So if I had to guess:
HT-12 = 20 Mhz and 4MB Ram
HT-18 = 20 Mhz and 16MB Ram
HT-21 = 25 Mhz and 16MB Ram but needed a re-spin for some reason and was rare
HT-22 = 25 Mhz and 16MB Ram

Interesting read so far.

are the 18/21/22 pin compatible to be used with this PCB design or is this all academic?

maxtherabbit wrote on 2024-12-20, 15:19:

are the 18/21/22 pin compatible to be used with this PCB design or is this all academic?

18 and 22 look like they are 100% compatible, at a first glance at the datasheets.

18 https://theretroweb.com/chip/documentation/ht … 98435658181.pdf

Nexxen wrote on 2024-12-20, 16:37:

maxtherabbit wrote on 2024-12-20, 15:19:

are the 18/21/22 pin compatible to be used with this PCB design or is this all academic?

18 and 22 look like they are 100% compatible, at a first glance at the datasheets.

...but HT12 has 160 pins, while HT18 has 208 pins. Thus, a PCB redesign would be required on this motherboard to accommodate HT18+

feipoa wrote on 2024-12-20, 21:52:

Nexxen wrote on 2024-12-20, 16:37:

maxtherabbit wrote on 2024-12-20, 15:19:

are the 18/21/22 pin compatible to be used with this PCB design or is this all academic?

18 and 22 look like they are 100% compatible, at a first glance at the datasheets.

...but HT12 has 160 pins, while HT18 has 208 pins. Thus, a PCB redesign would be required on this motherboard to accommodate HT18+

Yes. He asked 18 to 22.
They have more internal circuitry, probably if you limited to 4MB of ram... IDK, an expert is needed to tell.

I'd like to find a seller for the HT12 though.

I have an HT18/B. It has 160 pins like the HT12. With a datasheet i could check if it is pin compatible.

Hi.
Great Project Nelson. Are the schematics available as open source?
I got my hands on an HT18 386SX Board. Now i´m playing with the idea of using the Chip for a 286 replica board.

Nelson68k wrote on 2024-12-20, 23:30:

I have an HT18/B. It has 160 pins like the HT12. With a datasheet i could check if it is pin compatible.

We discussed this in another thread, hoping for the same.
HT12 is 160 pin, HT18 is 208.

HT18 a,d 21/22 are pin compatible.

I wish we had a HT12 boardview...

ecuProg7 wrote on 2025-01-24, 14:49:

Are the schematics available as open source?

Not now. Later, when the beta testers no longer find any bugs.

Nexxen wrote on 2025-01-24, 17:08:

I wish we had a HT12 boardview...

This?

Nelson68k wrote on 2025-01-24, 20:36:

Not now. Later, when the beta testers no longer find any bugs. […]
Show full quote

ecuProg7 wrote on 2025-01-24, 14:49:

Are the schematics available as open source?

Not now. Later, when the beta testers no longer find any bugs.

Nexxen wrote on 2025-01-24, 17:08:

I wish we had a HT12 boardview...

This?

The attachment Bildschirmfoto 2025-01-24 um 21.44.18.png is no longer available

Nelson, this is great.

Nelson68k wrote on 2025-01-24, 20:36:

Not now. Later, when the beta testers no longer find any bugs. […]
Show full quote

ecuProg7 wrote on 2025-01-24, 14:49:

Are the schematics available as open source?

Not now. Later, when the beta testers no longer find any bugs.

Nexxen wrote on 2025-01-24, 17:08:

I wish we had a HT12 boardview...

This?

The attachment Bildschirmfoto 2025-01-24 um 21.44.18.png is no longer available

Having the pin connection scheme, you can have the board made, and then you have to solder all the necessary components, maybe 🤔 who has a too damaged board, could make it work again with a new PCB.
For example, I kept an old 386DX from the late 80s, maybe 🤔 it could be repaired with a lot of (a lot of) work, but having a new PCB made, ultimately could be the easiest solution, because you don't have to go in search of traces interrupted by corrosion.

Test the maximum speed. At the moment it is running stable at 24.58 MHz.