Intel Wildcard 88 Motherboard

The goal of this project is to design and build an IBM PC/XT compatible motherboard utilizing the Intel Wildcard 88 module.

Intel Wildcard 88

The Intel Wildcard 88 module was announced by Intel in August 1988. In early 1990's Intel sold Wildcard 88 line to Canadian Megatel Computer Corporation (here is their Wildcard 88 page).

The specifications of Wildcard 88 module:

• • The size is about 2" x 4" (50.8mm x 101.6mm)

  • Intel 80C88A CPU - 4.77 MHz, 7.15 MHz turbo mode, and 9.54 MHz (Wildcard-88-10N only)

  • A custom ASIC implementing functionality of most 82xx ICs (8259 PIC, 8254 PIT, 8237 DMA, 8255 PPI, 8284 clock generator, 8288 bus controller) and glue logic found on an XT motherboard.

  • Half a dozen of 74ALS244 buffers, 74ALS245 transceivers, and 74ALS373 latches to buffer signals going out of the module.

  • Socket for ROM BIOS. 8 KiB (2764 type), 16 KiB (27C128 type), and 32 KiB (27C256 type) EPROMs are supported.

  • Socket for 8087 math co-processor (MPU) - On 'N' models only.

  • 68-pin SIMM edge connector to connect to the system board. The connector contains all signals found on an XT bus (8-bit ISA), signals required to interface to DRAM (CAS, RAS0 - RAS2, /DRAM, MUX), signals for XT keyboard, speaker output, external reset and video configuration inputs (on 'N' models only)

The Intel Wildcard 88 module was used in several XT compatible computers, for example in The Leading Edge Model D computers (made by Daewoo). One of more unusual applications - it was used as a control module for Nikon NASA F4 camera, one of the first digital cameras that flew on several Space Shuttle missions.

The Motherboard

Overview

Most of the XT computer functionality is implemented on the Wildcard 88 module. The motherboard adds memory, ISA slots, and AT2XT keyboard converter (so that the motherboard can be used with a more modern PS/2 keyboard). It is designed to be as small as possible (board size 4.6" x 6.5"), but yet functional enough to be used as a generic XT motherboard.

Specifications

Here are motherboard specifications and ideas behind them:

• • 5 ISA slots. Number of slots it tradeoff between board size and extensibility. 5 slots should be enough (the same number as on the original IBM PC motherboard), assuming the slots will be used for the following cards:

    1. Display card

    2. Floppy disk controller card

    3. Hard drive controller card, e.g. XT-IDE or XT-CF-Lite

    4. Audio card

    5. Available for other extension cards (e.g. network).

  • Memory is implemented using single 1 MiB (1 Mbit x 8) SIMM-30 module. The motherboard memory support circuit includes three 74*157 multiplexers (used to generate DRAM row / column addresses), 74*245 buffer for the data bus, 74*27 NOR gate used to generate a single /RAS signal from RAS0 - RAS2 signals supplied by the Wildcard 88, and to invert CAS signal. Two otherwise available multiplexers are used to buffer and delay /MEMW signal to memory.

  • Motherboard provides PS/2 compatible Mini-DIN keyboard connector. The Wildcard 88 provides an XT compatible keyboard interface. Motherboard includes an AT2XT keyboard converter, implemented using a PIC12F629 microcontroller.

  • Power supply: Motherboard is powered using a 8-pin connector, with 5V, 12V, and -12V voltages. Motherboard includes an LM7905 power regulator is used to convert -12V to -5V. Four diagnostic LEDs are included on the motherboard to indicate voltage on each power rail. An additional 5V connector on the motherboard can be used to connect power to 3.5" floppy drive.

  • Motherboard includes a 12 mm speaker, and a header for connecting an external speaker.

  • Jumpers, switches, and connectors:

• • • Reset switch (6 mm tactile button)

    • P5 - Reset header (for external reset switch)

    • P6 - Power LED

    • JP1 - VID0 - Video configuration jumper (mono / color)

    • JP2 - AT2XT keyboard converter configuration. Currently, if installed, the jumper configures firmware to pass 0xE0 scan code to the system. This is useful for international keyboards.

Bill of Materials