Here a small 8-bit computer shall be presented.
It has been realized so far on these FPGA boards:
Spartan-3A/3AN Starter Kit from Xilinx
Spartan-3E Starter Board from Digilent
Nexys2 Board from Digilent
Terasic/Altera DE1 board
Terasic/Altera DE0 board
Terasic/Altera DE0-nano board
Waveshare OpenEP4CE10 Board
The CPU has a complete instruction set with 256 opcodes.
It can address an indefinite number of 64K-pages and is
optimized for biggest simplicity. So it has no interrupts.
Calculating the duration of instruction-sequences ist easy.
The total system consists of the four 64K-pages
ROM/video-RAM, main-RAM, addition-RAM, selected slot.
There are 8 slots for expansion-cards. In the realization on
FPGA boards the slots exist only from view of the software,
indeed the expansions are part of the mainboard.
The software includes a text editor, an assembler and a high
level language. Parts of programs, even in high level language,
can be written so, that the duration can be calculated exactly.
The character set includes a hexadecimal set of digits,
where the digits A to F are represented by modified
versions of the letters A to F.