Just a small update on the status of the DIY CPU:
The circuit design of the main CPU components is completed. The layout was split up in six parts :
- ALU and Shifter
- Index Registers
- General Purpose Registers and Program Counter
- Clock and External Bus I/O
- Microcode Sequencer
Each part occupies an 160x100mm circuit board. The boards are interconnected with pin headers to provide access to the internal data and address bus and to distribute the clock signal.
Parallel to the layout the circuit was constructed in a simulation tool to test correct function. To fill the microcode storage with meaningful code, a Delphi program was written to generate the microcode sequences for the opcodes.
This program was used to implement the microcode for a few basic opcodes which were then used to write a small assembler program that calculates the fifth fibonacci number (see screenshot).
I’m currently working on some other projects to get some distance from the CPU. This helps to spot errors when looking over it a few weeks later. Then a few additional circuit boards for data I/O and storage/RAM will have to be designed.