And now, with pleasure, I present the hero of our next quest - the JUKO ST-12 TURBOXT motherboard with 640KB RAM, featuring a NEC V20 12MHz processor and an Intel 8087-2 coprocessor!

By the way, what expansion cards do I have for further start of the motherboard? Interesting cards, but does anyone see a graphics card or a bootable disk controller? I don't see one either(((

First graphics card and first modification

Modification of the Trident 9000I graphics card to work in an ISA8 slot. Cut the trace from contact B28 and add a wire to B29.

Hooray! We now have an image on the screen)))

Hi,

I'm actually reading this thread with interest, I just don't felt the need to comment on it yet as I'm not experienced with NEC V20 CPUs, so I didn't had anything useful to add yet.

However in your last post the modification of the graphics card is a really nice solution to make it work in a ISA8 slot, but from personal experience those pin modifications will become hard to notice when later visually inspecting the card, so to avoid the confusion that I suffered from forgetting one of my similar modifications I would recommend putting a sticker on the card writing down that the pins are modified somewhere for future reference, it is sometimes hard to remember those modifications after some years pass, and it is a good reminder that the card is modified in some way if it will be used in another system.

Otherwise very interesting and nice project 😀

MagefromAntares wrote on 2026-06-03, 06:32:

Hi, […]
Show full quote

Hi,

I'm actually reading this thread with interest, I just don't felt the need to comment on it yet as I'm not experienced with NEC V20 CPUs, so I didn't had anything useful to add yet.

However in your last post the modification of the graphics card is a really nice solution to make it work in a ISA8 slot, but from personal experience those pin modifications will become hard to notice when later visually inspecting the card, so to avoid the confusion that I suffered from forgetting one of my similar modifications I would recommend putting a sticker on the card writing down that the pins are modified somewhere for future reference, it is sometimes hard to remember those modifications after some years pass, and it is a good reminder that the card is modified in some way if it will be used in another system.

Otherwise very interesting and nice project 😀

Hi!
Tnx for info and interest to my topic.
Trident modification is temporal just to get something on screen as fast as possible
My target is ISA8-only configuration with ISA8 videocard 😀

Let’s take a closer look at the motherboard and examine the memory sockets, ROM chips, crystal oscillators, and jumpers!

1) The motherboard natively supports from 256 KB to 1 MB of RAM.
The exact RAM configuration is specified as a DRAM chip installation diagram in the user manual, and requires proper jumper settings on the SW-A configuration block.

2) There are two sockets on the board for installing ROM chips.
The first socket is labeled 2764 inside the socket footprint and is intended for the primary BIOS 8KB ROM chip.
The second socket is labeled 27256 inside the footprint and is designed for a supplementary 32 KB ROM chip.
(We will return to this one later and try to use it as a BIOS ROM EXTENSION to expand the primary ROM capability and ensure seamless operation with optional expansion cards).

3) The motherboard features two crystal oscillators that determine the CPU clock speed.
In my case, the first crystal operates at 14.31818 MHz, providing a 4.77 MHz clock speed for the CPU in DE-TURBO mode.
The second crystal operates at 24 MHz and gives a 12 MHz clock speed in TURBO mode.
(If your second crystal is rated at 20, 24, or 30 MHz, your TURBO mode speed will be 10, 12, or 15 MHz respectively).

4) The board features jumper J6, which configures the wait state mode: WS0 (0 wait states — a faster operation mode) or WS1 (1 wait state — a more compatible but slower mode for memory and expansion cards).
If parity chips are populated in the memory parity sockets (4 sockets labeled as 21256), the parity check feature can be enabled via the PAR switch on the SW-A block.

Solving the issue with boot devices.

I bought a beautiful multi-card (1xLPT, 2xCOM, 1xGAME, FLOPPY, RTC) in ISA8 format.

In addition to this (since my ISA8 SCSI controller is not bootable), I decided to use the ROM socket on the motherboard (labeled as 27256) as a ROM BIOS EXTENSION and flashed the FUTURE DOMAIN TMC-850/950 SCSI BIOS ver. 8.5 into it.

I am very interested in this project, and I will keep an eye on the progress of this thread.
I have several JUKO motherboards, and I've been struggling with how to utilize them. I use a Realtek 3105 graphics card for display output, which can be used directly without modification.

Meanwhile, I flashed the 8KB Super PC/Turbo XT BIOS 3.1 into a W27E257 EEPROM, and it successfully booted in the 2764 ROM socket!
Furthermore, I inserted another W27E257 (configured as OTP) containing the FUTURE DOMAIN TMC-850/950 SCSI BIOS ver. 8.5 into the second 27256 socket, and it worked as well!

The motherboard is indeed (for now) compatible with 8KB BIOS images in the ROM socket labeled "2764". The following configurations have been tested and verified to work (albeit with some quirks specific to my hardware setup):

1) Native Juko TurboXT BIOS 2.32: It works, but the system fails to POST/boot if any version of the FUTURE DOMAIN SCSI BIOS is inserted into the second 27256 socket.

2) The sleek and modern GlaBIOS (latest version): It works. Upon powering on, the video card BIOS initializes first, followed by the motherboard BIOS. At a certain point, the SCSI controller BIOS initializes and detects the hard drive, but the system fails to boot from the HDD.

3) The equally sleek Super PC/Turbo XT BIOS 3.1: This is currently the optimal choice. It functions exactly as shown on screenshot: on power-up, the video card BIOS executes, followed immediately by the successful initialization of the SCSI controller BIOS, and only then do the motherboard BIOS messages appear. Booting from the HDD works flawlessly.

Expanding RAM to 1024KB

The 44256 dynamic memory chips have arrived (I ordered 10 pcs. as a spare, since many currently sold are refurbished and relabeled). I got lucky and all the chips turned out to be working. Soon we will find out how to use the additional 384KB of memory on this motherboard.

Videocard change and final configuration for today

1) 1MB RAM installed on the motherboard

2) MSDOS boots with 1GB SCSI HDD and Future Domain TMC-850 SCSI controller

3) Soundcard is late Adlib clone

4) Multi-card ISA8 with 2COM, 1LPT, 1GAME, 360/720KB floppy drive interface and RTC

5) Video card Oak OTI-037 ISA8

BIOS Difficulties (Part 1).

For most of the time, my rig ran with PCXTBIOS 3.1 from 2017. I made minor cosmetic adjustments, and mostly I was satisfied, except that this firmware did not test (and did not count) the 384KB of expanded memory on my motherboard.

As an alternative, I tried to launch the latest version of GlaBIOS (which exists in a variant for my chipset). Here I encountered the following unpleasant issues: the computer refused to boot from HDD, while booting from FDD was stable only in de-turbo mode at a processor frequency of 4.7MHz (in turbo mode at 12MHz, there were random hangs, errors, or simply a refusal to boot).

I contacted the GlaBIOS author, and quite quickly we found a solution that allowed achieving boot from HDD. It was sufficient to recompile the BIOS by activating the INT_19_BOOT_HD flag in the BIOS source code.

However, solving the issue with booting from FDD took a bit more time. The first working option was to leave the GlaBIOS microchip in the main ROM socket, and insert a 27256 microchip with three BIOS ROM EXTENSIONS flashed into it into the additional socket:

1. FD TMC SCSI BIOS v. 8.5 (for the ability to boot from HDD)

2. Floppy BIOS for this card - https://theretroweb.com/expansioncards/s/ast-ck-7260 (this firmware worked stably and allowed booting from FDD in turbo mode)

3. GlaTICK (support for real-time clock on my multicard. A very useful addition from the author of GlaBIOS).

BIOS Difficulties (Part 2).

So, I obtained a fairly stable system, but with a mix of all possible BIOS extensions and a small patch during system boot (setting parameters of my 3.5' floppy drive to 720KB with the DRIVPARM command in the config.sys file).

And then the epiphany! I remembered that in the mid-90s on my 386DX40/4MB/420MB IDE, I experienced random hangs when working with the floppy drive together with the OAK OTI-037 videocard.
I immediately returned the Trident 9000i to the build and confirmed that with it, at a processor frequency of 12MHz, hangs when working with the floppy drive do not occur.
Well, let's examine the jumper on the OAK videocard! In my case, there are only two (the first switches the monitor to B/W mode), there is no information about the second one (following the analogy of similar video cards on TRW, it most likely controls IRQ operation). By default, the jumper was in the CLOSED position - I switched it to the OPEN position and my system successfully boots at 12MHz with the OAK OTI-037 video card!

After this, I changed the firmwares of the 27256 microchip to the following set of BIOS extensions:

1) GlaTICK (RTC support)
2) GlaDISK (floppy BIOS extension from GlaBIOS author with correct support of my 720KB floppy drive)
3) FD TMC SCSI BIOS v. 8.5 (for the ability to boot from HDD)

PS. RTC clock on my multicard can be set to port 240h or port 340h. It is better to set it to 340h because games and applications with Soundblaster support on port 240h can disrupt the time/date values of the RTC clock.

Looks good so far! Well done! 😎👍

Let's do something with 384KB!

Since there is an additional 384 KB of RAM on the mother's memory (with a very unusual organization, reminiscent of "mappers" in game console cartridges) - let's try to use them somehow.
As a standard, this motherboard only has a proprietary RAM-disk driver, which allows them to be used as a virtual disk with a capacity of 384KB. This is already good and you can place there, for example, a part of the operating system (command.com) and some small file manager like Volcov Commnader. This solution is especially useful on authentic builds that use floppy drives and/or vintage hard drives to boot and run, significantly reducing the load on them and extending their lifespan.
As an alternative - there is an EMS memory driver from 1991 (author George Lefterov, he is definitely on VCFED and I don't know if it is on this forum). There are a number of nuances with this driver. The main question in my case is since the driver checks that the full amount of RAM before booting the system is 640KB and does not boot in other cases, and I have the amount of RAM due to the presence of SCSI BIOS the amount of RAM was 639KB. Unfortunately, The source code of the driver has not been preserved and the driver itself is partially encoded.
With the help of a friend, we managed to fully decode and disassemble this driver, while eliminating a couple of minor bugs that ended up inside (hopefully not to the detriment of its functionality). Now the source code (with the addition of the ability to use less than 640KB of free RAM is uploaded to GITHUB, and those who wish can either build it themselves or make edits or use a binary driver)!
The stable operation of this driver apparently requires further improvements, but it is already functioning, tested by working with CHECKIT, some other tests, the EMSDSK driver for creating a RAM disk of arbitrary size in EMS memory.

https://github.com/indrekis/JukoST_EMS

Weird chipset choice to map this ram to a window at 2000:0 (128KB) instead somewhere at the top. Makes EMS emulation very slow (copying data around).

Love indrekis blog, had to resort to google translate to read but it was worth it https://indrekis-github-io.translate.goog/ret … &_x_tr_pto=wapp
all blog posts https://indrekis-github-io.translate.goog/pos … &_x_tr_pto=wapp

rasz_pl wrote on Today, 10:35:

Weird chipset choice to map this ram to a window at 2000:0 (128KB) instead somewhere at the top. Makes EMS emulation very slow (copying data around).

Love indrekis blog, had to resort to google translate to read but it was worth it https://indrekis-github-io.translate.goog/ret … &_x_tr_pto=wapp
all blog posts https://indrekis-github-io.translate.goog/pos … &_x_tr_pto=wapp

Speed is not my interest with this XT
I want functionality and investigate dark-zones of motherboard and chipset)))

One more thing!

I had planned to use a SCSI CDROM in this rig, but suddenly I got a wonderful and working 2x SONY CDROM with SONY 34pin interface, complete with a universal ISA8 SONY/PANASONIC/MITSUMI controller