This was a project I worked on in the winter of 1999 because
I had never designed and built a computer from the ground up.
The Motorola MC68k was chosen because I
think that processor's architecture is interesting.
(It also wasn't an Intel chip.)
The basic design has the low memory (vector table) and a simple monitor program in ROM.
Two megabytes of RAM are available.
Hardware is mapped to the upper megabyte block of the address space.
A couple of PLDs decode the addresses and generate varying bus cycle lengths for
different memory areas and hardware types.
The asynchronous I/O bus of the MC68k is quite different from the synchronous bus of
the Intel processors (8085, 8088, 8086).
One of the PLDs generates the signals necessary to interface with the 8272 FDC (an Intel chip).
The other reason that I chose the 68k was the there were good software development tools (GCC et al.)
and a monitor (VUBUG) available for free.
The monitor was from Vanderbuilt University.
I converted it to compile under GAS (GNU's assembler) and modified it to function in a memory
space greater than 64 kilobytes.
I used a Linux as a development environment and then download code through the board's second
serial port.
The first serial port was connected to a terminal emulator running on the Linux box also.
The board is constructed on a single sided perf board with a single pad per hole.
All the connections were made with wire-wrap wire stripped and soldered at each end.
The pile of wire in the middle is about 3/4 of an inch thick.
I have the floppy drive reading and writing sectors.
I began to port XINU.
An IDE interface was sketched out, but never implemented.
