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Homebrew PC XT (Was: PC XT homebrown?

N

neazoi

New Member
Joined
Sep 2, 2009
Messages
8
hello all this may be a bit crazy but I would like to build my own PC XT motherboard. Is there anyone else that has done so or do you know of any kits sold in the internet?

Specs:
CPU 8088 or V20
Bus 8-bit ISA

I have build elector magazine solid state floppy and run my ms-dos from this one! but a motherboard kit or complete project (schematic, bios code, pcb pattern) would be very interesting.

Thanks
 
Steve Ciarcia did one back in 1983 called the MPX-16. It was a DIY clone board that had some interesting features, but I don't think was completely compatible with the IBM. The entire project was featured in early 1983 BYTE magazine.
 
Securix said:
Steve Ciarcia did one back in 1983 called the MPX-16. It was a DIY clone board that had some interesting features, but I don't think was completely compatible with the IBM. The entire project was featured in early 1983 BYTE magazine.
Click to expand...

There were a couple of Heathkit-style "solider-it-in" kits early on. I've got a board from J&L labs that's the memory and async (uses an 8274) parts of one. I've also got the schematics for another (not-quite-PC-compatible, but close) kit, but the name escapes me at the moment.

I recall that Ciarcia's series didn't have a video card per se, but used serial output to a terminal (which made sense back then).
 
I think building an 8086 board with 16 bit ISA would be spiffy :p
Maybe throw on a paged MMU with remapping support so you could remap the memory layout for other OSes or such...
Perhaps use a V30 instead, as it has the 286's non-protected mode instructions.
the 186 would be nice except for the non-compatible integrated controllers and periphery.

I wonder how much you could really do with a 10Mhz 8086 if you glued it to as much modern hardware as you could. Is 10Mhz as fast as they made 8086s?
 
Hi Andrew,

I was thinking 80188EB and you beat me to it!

Even better, if you can find a NEC V40, the peripherals are much closer to the PC.

The problem is that the PC-era chips are getting harder to find...
 
Hi Chuck! Thanks! Occasionally there have been some discussions of an 8088or 80C188 style SBC on the N8VEM project but nothing has come to the prototype phase yet that I know about. Hopefully it will happen eventually.

Whether it is PC compatible or not isn't so important to me at least. There are many 8088 style OSs that will run and PC compatibility is probably more hassle than it is worth. CP/M-86 is nice as is FreeDOS and they can be ported to most any x86 style system and provide a lot of functionality.

Thanks and have a nice day!

Andrew Lynch
 
Hi Andrew,

For me the tipping point is applications, not OS. The further you get away from plain old PC-type MS-DOS, the thinner the offerings become--and rapidly.

This isn't like the 8-bit situation, where there were many incompatible manufacturers.

As a developer of an early 80186 sort-of-compatible, I recall with much pain how difficult life became when support for PC applications could not be provided.
 
I had thought this would be a cool project too, but I keep hitting the stumbling block, "why?" I know you don't necessarily need a good reason to do this. ;)

I had thought a couple good projects for XT machines would be an EMS memory expansion card, and/or an 8-bit 10baseT adapter.
 
geoffm3 said:
I had thought a couple good projects for XT machines would be an EMS memory expansion card, and/or an 8-bit 10baseT adapter.
Click to expand...

I've love these! Maybe after XT-IDE?
I really don't have any design experience, but would love to help test.
I think it would be sweet to make our own 8bit super-expansion card with ram, storage, video, ethernet, maybe upgraded serial ports with 16550 compatible uarts etc. Put as many functions on one card as we could work... would be awesome for certain 8bit machines with only one isa slot (I'm looking at you Tandy 1000RL!!!)

I've been dreaming about that since I was a teenager... Really don't know why I love my 1000RL so much, but it has plenty of draw, and I love how quiet it is without any fan.
 
geoffm3 said:
I had thought a couple good projects for XT machines would be an EMS memory expansion card, and/or an 8-bit 10baseT adapter.
Click to expand...

According to 3Com, the 3C509B works in 8-bit mode if you plug it into an 8-bit slot. This only works with the 3C509B, not the regular 3C509.
 
If it's ethernet you're wanting, don't forget the ethernet-enabled microcontrollers and their support chips, such as the Microchip ENC28J60. There are a fair number of uCs with WiFi support also.

They might be easier to work with.
 
FishFinger said:
According to 3Com, the 3C509B works in 8-bit mode if you plug it into an 8-bit slot. This only works with the 3C509B, not the regular 3C509.
Click to expand...

Interesting...I didn't know that! Not surprised that someone would have support for 8-bit mode.

Seems like a modern memory expander that uses at least SIMMs might be good.

Another thing that would be good for an XT motherboard project (or standalone...probably someone doing this now) would be a USB keyboard controller instead of the standard XT style.
 
geoffm3 said:
Interesting...I didn't know that! Not surprised that someone would have support for 8-bit mode.
Click to expand...

I've just double checked, and this was the quote:

3COM said:
Question: Will the 3C509B work in an 8-bit slot in an IBM PS/2 model 30?

Answer: Yes. The 3C509B family needs at least a 286 processor to function, but will work in an 8-bit slot. An original 3C509 will not.
Click to expand...

So no luck with 8088/86 systems. I'm not sure what the issue is though, whether the driver software uses 286 instuctions, or the hardware needs the extra IRQ/DMA lines of the 286+ systems.
 
FishFinger said:
I've just double checked, and this was the quote:



So no luck with 8088/86 systems. I'm not sure what the issue is though, whether the driver software uses 286 instuctions, or the hardware needs the extra IRQ/DMA lines of the 286+ systems.
Click to expand...

Couldn't be that I wouldn't think... since there's no additional 286+ specific DMA/IRQ lines on the 8-bit slot.

I wonder if maybe a V20 equipped system would work if it's a code compatibility issue? Doesn't that have some of the 80286 instructions in it?
 
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