0 - The 8088

Author: sgeorge, Posted on: 27 June 2016 21:43

A new project appeared on the horizon, Sergey Kiselev created the Xi 8088 pcb, which is an 8bit ISA board that sits in a backplane.

Pretty cool homebrew board.

Yep, I snagged one.

After lots of soldering of sockets, jellybeans, we get a semi naked board.

Time to add our old school 74F series chips.. Al of them came from mouser apart from the 74F11 which came from ebay, along with the core support chips.

Running it, is the beastly 16mhz NEC-V20.

So, I didnt have a proper AT PSU on hand, so I used my fluke bench PSU's to create a +5/+12/GND, and it would post (play its 5 note tune) but I'd get not VGA output.

Turns out I needed a full AT PSU, so something is looking for -5 or -12VDC.

Once I had that sorted things looked good.

I tested 'turbo' using a 24mhz oscillator, which runs the CPU at 8mhz, that was ok. I then tesetd my 40mhz oscillator, which runs the CPU at 15mhz, that failed to post, well the card posted but the VGA card did not.

I tried changing the wait states but could not get it to post, so I need to get a 36mhz oscillator and see if it will post at 12mhz.

So whats the plan Stan? Well, a long long time ago in the fun days of MS-DOS and instant reboots, I started writing a DOS clone. I thought it would be fun to try and get that back up and running, targetting the XT class 8bit x86 hardware.

To that end I've got a build in the works for a second ISA shoebox build around the Xi8088 board.

Of course, we need a venerable 8bit network card, fortunately for us this 3COM 3c503 has both a dsub connector and an proper rj45 socket, so no adapters required.

I've also to build Sergey's XT-CF-Lite card that can run a CF card as a hard drive since this has no controller cards in it, nothing beyond the CPU board.

I will probably have to pick up a floppy controller or something. Will see.

Gonna drop in an adlib clone (also done by Sergey!) or a Sound Blaster 2 (last of the 8bitters!).

Getting video output working was a bit of an effort. The 8088 is a essentially an 8086 with an 8bit bus... that means 16bit slots dont work. One has to choose their cards carefully.

I dont have any monitors around that can handle CGA or EGA, they are 15khz, which leaves me to get a VGA card (standard 31khz) so it can work on an LCD..

After lots of searching around on the vogons and vitage compter forums I managed to track down a Triden 512kb VGA card that will work in 8bit mode and has an XT compatible BIOS (quite a few cards work in 8 bit mode but apparently have 286+ instructions.. doh!).

I had to solder a 2x3 set of jumper pins to the board, which was a bit of a pain as the Hakko 808 desolder gun wasnt havnt the best time on this old solder, the holes were small and filled in, probably wave soldered or something...

But it worked!

So the plan is another shoebox build based roughly on the following;

  • Slot 0 - Xi8088 cpu board
  • Slot 1 - Trident VGA (TVGA9000B) jumpered for 8bit
  • Slot 2 - XT-CF-Lite compact flash hard disk controller (8bit)
  • Slot 3 - 3COM 3c503 Etherlink II 8bit network card
  • Slot 4 - Adlib clone or SoundBlaster 2.0 card

tags: Sergey Kiselev, XT, Xi8088


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