IBM PC XT homemade?

[neazoi]

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

 

[per]

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

It's possible, but I think you need a little more than just a bus and a CPU. In fact, you need a lot more; what I'm talking about is the following:

(CPU)
(8-bit ISA bus)
Memory (RAM/ROM)
Interrupts (8 levels)
DMA (4 channels)
Timer/Counter (3 of them)
Low level System controll (a parallel I/O chip does this job just fine)
Keyboard-input interface
PC-Speaker interface
Clock generator
Wait-States (In cause you're using DRAM)
Interfaces between all of the above

 

[Chuck(G)]

There were a few kits out in the day.

One of the computer mags had a PC-like serialization of a construction project. ISTR that it used serial I/O for communications rather than direct video display. And there was always the Heath/Zenith H/Z-150.

But I don't know where you'd get an unassembled kit from that time.

If you wanted to roll your own without using a lot of parts, you could probably come very close to a PC XT if you used a chip like the NEC V40 (has UART, DMA, CTC and memory refresh on-chip). You could use a single 4Mb ( 512Kx8 ) SRAM and avoid the issues of correct DRAM design altogether.

 

[neazoi]

I have found some technical manuals for ibm pc-xt on ftp.oldskool.org. these are very fine and even give the bios code. but there are no pcb patterns (

I wonder if anyone has ever done a complete pc-xt project for the others fo be able to reproduct it if having fair good electronic skills.

I know there are some issues from old magazines but I have not got any

 

[wrljet]

There were a few kits out in the day.

One of the computer mags had a PC-like serialization of a construction project. ISTR that it used serial I/O for communications rather than direct video display. And there was always the Heath/Zenith H/Z-150.

But I don't know where you'd get an unassembled kit from that time.

If you wanted to roll your own without using a lot of parts, you could probably come very close to a PC XT if you used a chip like the NEC V40 (has UART, DMA, CTC and memory refresh on-chip). You could use a single 4Mb ( 512Kx8 ) SRAM and avoid the issues of correct DRAM design altogether.

If you want a "PC" that'll run DOS programs, you'll want true hardware compatibility including I/O addresses. The built-in peripheral chips in, say the 80188, are not addressable that way. I built a machine with a V40 twenty years ago, but it wasn't PC compatible, (fuel injection controller) and I don't remember if those I/O address were configurable or not. (pic of that attached for the heck of it)

Bill

 

[TandyMan100]

If you want a "PC" that'll run DOS programs, you'll want true hardware compatibility including I/O addresses. The built-in peripheral chips in, say the 80188, are not addressable that way. I built a machine with a V40 twenty years ago, but it wasn't PC compatible, (fuel injection controller) and I don't remember if those I/O address were configurable or not. (pic of that attached for the heck of it)

Bill

Woah. I. Want. To. Build. That.

What OS does it run? Could you PM me with details to how it was maide? Perhaps schematics?

 

[Chuck(G)]

If you want a "PC" that'll run DOS programs, you'll want true hardware compatibility including I/O addresses. The built-in peripheral chips in, say the 80188, are not addressable that way. I built a machine with a V40 twenty years ago, but it wasn't PC compatible, (fuel injection controller) and I don't remember if those I/O address were configurable or not. (pic of that attached for the heck of it)

There are laptops that used the V40 that ran MS-DOS programs just fine (e.g. Sharp PC 4641). The V40 is a lot closer to a "real" PC than, say, an 80186. You can configure the onboard peripheral addresses to conform to the PCs. For most MS-DOS programs, all you need is BIOS compatibility.

The interrupt controller on the V40 looks a lot like an 8259; the counter-timer looks like an 8253. The UARTs look like 8251s, not 8250s, but don't have sync capability. And the port addresses are configurable.

 

[NobodyIsHere]

Hi Chuck! There is an N8VEM builder who is interested in making an 8088 style Eurocard SBC as an alternate to the current Z80 SBC. I think this is a great idea.

Do you have any suggestions for an 8088/80C188/V40 circuit that uses through hole parts that is compact enough to fit on a Eurocard and still have enough room for the logic to drive an ECB (Z80 pin out clone bus)? I am trying to avoid programmable logic but this would be a stretch for sure.

That's a pretty tall order when you are limited to less than 30 ICs max.

Thanks and have a nice day!

Andrew Lynch

 

[wrljet]

There are laptops that used the V40 that ran MS-DOS programs just fine (e.g. Sharp PC 4641). The V40 is a lot closer to a "real" PC than, say, an 80186. You can configure the onboard peripheral addresses to conform to the PCs. For most MS-DOS programs, all you need is BIOS compatibility.

The interrupt controller on the V40 looks a lot like an 8259; the counter-timer looks like an 8253. The UARTs look like 8251s, not 8250s, but don't have sync capability. And the port addresses are configurable.

Yeah, my memory is worn out, but I did select that chip 20 years ago, I don't remember why. They are nearly unobtanium now, though, I would imagine.

Bill

 

[wrljet]

Woah. I. Want. To. Build. That.

What OS does it run? Could you PM me with details to how it was maide? Perhaps schematics?

You don't want to build one of those. It's an embedded controller to run a car engine. Doesn't run an "OS" proper. The app is written in assembler.
Construction is wire-wrap on a PC prototyping card (which I had loads of at the time 20 years ago). I used the V40 because I happened to be employed at the time laying 386 code so it was easy to use that x86 chip for my hobby.

Bill

 

[Chuck(G)]

Hi Chuck! There is an N8VEM builder who is interested in making an 8088 style Eurocard SBC as an alternate to the current Z80 SBC. I think this is a great idea.

Well, the 8088 is out for certain--too many support chips required. The V40 (NEC 70208)comes in PLCC and is closest in architecture to a PC, but may be hard to find in quantity. The Intel 80C188 has a couple of variants in PLCC. The -EA is the basic chip; the -EB has two serial ports, but leaves out the DMA controller.

Both the NEC and Intel chips multiplex the data and address bus, but that shouldn't be too hard to unravel. I think you could do it in less than 30 glue chips.

There are single chip PCs (STM, Vadem), but they're QFP packaging, and use keypad and LCD interfaces and are intended mostly for handheld applications.

 

[wrljet]

Another chip is the NEC V25. I built a small embedded system with one of those many years ago. I don't know if those chips were ever popular or not.

Bill

 

[Chuck(G)]

The NEC V25 family (V25, V25 plus, V35, V35 plus, V25 Software Guard...) are a little too different internally to make good candidates for XT-type systems. The on-chip peripherals are memory-mapped and very different from commodity x86 support chips, interrupt processing is done through switching register sets, rather than stack operations. The Vx5 series was intended for embedded applications; some members have on-chip program ROM.

On the other hand the V53 (uPD70236) would be a perfect candidate; it seems to have been made just for the XT-compatible market--but for two considerations that would make it unsuitable for Andrew's needs. The first is that it comes in only two package styles--QFP and PGA. The second is that it's got a 16-bit bus--there exists no 8-bit version (V43?). But for someone wanting to "roll their own" it would be ideal, if they didn't mind working with the packaging.

The NEC V-series was fairly large and not well known here. Some may know them from some Sega consoles using the V60 and V70 chips.