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Homemade PC-XT clone motherboard info

N

neazoi

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Sep 2, 2009
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8
Hi,
I am looking for a motherboard to match this that I am trying to build http://microwave.gr/giannopk/computer.htm
As I say in the page the lowest count component the better.

I would dare to ask if anyone can provide a PC-XT 8088 or V20 motherboard schematic AND PCB layout?

This is tough but someone may have already scan these old magazines od done the reverse engineering job already?
 
Hi! Interesting! Please keep us posted on your progress.

Thanks and have a nice day!

Andrew Lynch

PS, I recall there used to be companies your could order PCBs for various XT ISA boards including motherboards. They included schematics, parts lists, and PCB layouts. I haven't seen any in a long time but if one could locate a cache of those it may accelerate your project.
 
They exist, but are probably not easy to find nowadays. Steve Ciarcia, I believe published the plans and board layouts for an 8088 system, but it was somewhat incompatible with the standard PC. I'll dig around and see if I can find anything. Note that a complete board is likely to be multi-layer.
 
Chuck(G) said:
Note that a complete board is likely to be multi-layer.
Click to expand...

Chuck,
That was what I was wondering about. Maybe some of the early boards were simple two sided boards, but somewhere along the way, the vendors would has gone to internal layers to increase parts density.
-Dave
 
Hi! Yes, no doubt the advanced boards would multilayer since they could get the costs down with huge quantity. Unfortunately for home brew style PCBs 2 layer is really the only cost effective option. 4 or more layer PCBs are very expensive.

My tool set supports multilayer boards but there is not much point in making them since the unit cost would be so high no one would want them.

I remember "back in the day" making several PC ISA peripherals using PCBs I ordered from Computer Shopper or the like. I'd get parts from Jameco or JDR and build them up for pretty reasonable. Normally they'd work first try although sometimes they needed some help to fix. It certainly was a lot of fun to build though.

Also used to make ham radio stuff from PCBs like a VHF two meter rig and packet modems and the like. Ham radio was a lot of fun making equipment but I never really got into the DX or talking on the "net". Making equipment is one hobby I've never outgrown I guess!

Thanks and have a nice day!

Andrew Lynch
 
Andrew,
I admire you guys that can make their own PWBs. In the early 70's at Rockwell I saw the pros with their light tables and mylar. Later of course it all went to CAD and auto-routing, but those pros could make some dense interconnects that were sophisticated. They could execute the circuit designers specifications of guard bands, minimum length and transmission line parameters, etc. better than any CAD program.

At Rockwell they tried everything from CALMA, Daisy and Mentor Graphics, etc. trying to find a sustainable vendor. They all seemed to go out of business. While I never used the interconnect tools, I did use the "front end" tools of schematic capture and logic synthesis/analysis.

Best of luck to your interesting projects.

-Dave
 
dave_m said:
I admire you guys that can make their own PWBs. In the early 70's at Rockwell I saw the pros with their light tables and mylar. Later of course it all went to CAD and auto-routing, but those pros could make some dense interconnects that were sophisticated. They could execute the circuit designers specifications of guard bands, minimum length and transmission line parameters, etc. better than any CAD program.
Click to expand...

We often forget that ICs used to be done that way too. Most of the really good board layout people tended to hail from east of Istanbul (a PC way of saying "Asian"). You could explain exactly what you wanted and they'd deliver, with their mylar sheet, X-acto knifes, tape and india ink. And more than once, they'd come back and point out an error that you'd made.
 
I have a Taiwan clone of an IBM XT which is not multi layered, I think. Seeing through the PCB using full light I cannot find any middle layer. I think if multi layered PCBs were used the whole motherboard would be populated by the internal leyer(s). I mean there is no point for the company to spend more if only a few connections are desired to be done on the middle layer...
 
Hi!

This might be a helpful book.

"The Big Blue Seed" by Ray Kosmic (ISBN 1114496979)

Thanks and have a nice day!

Andrew Lynch
 
neazoi said:
I have a Taiwan clone of an IBM XT which is not multi layered, I think. Seeing through the PCB using full light I cannot find any middle layer. I think if multi layered PCBs were used the whole motherboard would be populated by the internal leyer(s). I mean there is no point for the company to spend more if only a few connections are desired to be done on the middle layer...
Click to expand...
Yeah, I don't see why a DIY motherboard would have to be multi-layered; not much more to an XT than the N8VEM, especially with modern (S)RAM chips etc.
 
Well, the point of many multilayer PCB isn't the connections, it's the signal propogation. Having a nice ground plane can solve a lot of problems. When you get into higher speeds, it's a necessity, not an option.
 
Chuck(G) said:
We often forget that ICs used to be done that way too. Most of the really good board layout people tended to hail from east of Istanbul (a PC way of saying "Asian"). You could explain exactly what you wanted and they'd deliver, with their mylar sheet, X-acto knifes, tape and india ink. And more than once, they'd come back and point out an error that you'd made.
Click to expand...

That's pretty cool. :D
 
Chuck(G) said:
Well, the point of many multilayer PCB isn't the connections, it's the signal propogation. Having a nice ground plane can solve a lot of problems. When you get into higher speeds, it's a necessity, not an option.
Click to expand...
Well, sure, if speed is an issue, or real estate or even FCC approval, but we're talking homebrew 8088 here; some of Andrew's gang have N8VEMs that are faster. And propagation's much less of an issue when you can replace a whole field of DRAMS with one or a few SRAMs...
 
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MikeS said:
Well, sure, if speed is an issue, or real estate or even FCC approval, but we're talking homebrew 8088 here; some of Andrew's gang have N8VEMs that are faster. And propagation's much less of an issue when you can replace a whole field of DRAMS with one or a few SRAMs...
Click to expand...

...Or replace an 8088 and peripherals with a NEC V40. Or replace the whole shebang (buf for memory) iwth a VIA CX700. Or just emulate the thing in an FPGA or uC...

Depends on how much of a "purist" you want to be... :)
 
Chuck(G) said:
...Or replace an 8088 and peripherals with a NEC V40. Or replace the whole shebang (buf for memory) iwth a VIA CX700. Or just emulate the thing in an FPGA or uC...

Depends on how much of a "purist" you want to be... :)
Click to expand...
Sho 'nuff; good for many a heated 'discussion'...

I belong to the school that keeps the original CPU and peripheral chips although faster versions are OK, replaces the old low density DRAMs with high density SRAM, and gets rid of any unnecessary glue chips; 100% compatibility, easier and cheaper to build, and smaller and less power-hungry. Same idea as Andrew's projects (although those darned Propellers seem to be sneaking in everywhere ;-)
 
Personally my brand of vintage purism basically says, don't use something more powerful than the machine itself to perform some kind of peripheral function, like using a 40MHz microcontroller to build an interface on a machine that only has an 8MHz CPU... I think it defeats the purpose more than using modern RAM chips - at least the RAM still functions the same even if it is smaller.
 
I found this thread almost by accident and I think it is a cool project. I really like the idea of building a PC clone with SRAM chips. Are there any schematic of a complete PC/XT board around?
 
nestor said:
I found this thread almost by accident and I think it is a cool project. I really like the idea of building a PC clone with SRAM chips. Are there any schematic of a complete PC/XT board around?
Click to expand...

The only one I know of is the schematics for the original IBM XT, as presented in their technical reference manual. It should be noted that the only thing seperating the actual system design from the PC is the lack of the casette hardware and enhanced memory support (the Mostek 4164 [64Kx1bit], the Mostek 41256 [256Kx1bit], the Intel 2118 [16Kx1bit], and some unidentified 128Kx1bit IC with similar pinout as the 41256).
 
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