The 80386EX Chip
The Intel® 80386EX™ microprocessor is an advancement on the 32-bit, 24-address-bit 80386SX™, which in turn is a cut-down version of the 32-address-bit 80386DX™.
It is fully compatible with the ‘386SX, but has 26 address bits, so can access up to 64 MiB of address space. Its main advantage, though, is that it has many on-chip peripherals that would normally be needed on the computer; so the chip is ideal for Embedded computers (which is where the “EX” designation comes from).
The on-chip peripherals are designed to be compatible with the IBM® PC™, and include:
- Power management (including SMM)
- DRAM Refresh Control Unit
- Chip Select Unit
- DMA Unit (2×8237)
- Interrupt Control Unit (2x8259A)
- Timer Unit (8254)
- Asynchronous Serial (2×16450)
- Synchronous Serial
- GPIO
The SBC 386EX Board
John R Coffman designed a board based on the 80386EX, and added a number of other peripherals and connectors too. The board is designed to work into the whole RetroBrew Computers EuroCard Bus family of single-board computers and expansion cards.
The SBC 386EX board includes the following peripherals:
- Socket for the 80387SX maths coprocessor
- 32-pin DIP socket for up to 512 kiB of ROM
- 20-pin DIP socket for up to 32 kiB of SRAM
- 72-pin SIMM socket for up to 32 MiB of DRAM
- 96-pin EuroCard Bus connector
- Real-Time Clock with SuperCap power retention
- 10-pin RS-232 serial connector
- 1.8432 MHz crystal for precise RS-232 bit timings
- 40-pin IDE connector
- Micro SD card connector
- 4x debug LEDs
Coding and Electronics 