I've already been working on this for about two years, but figured I might as well also give the project a profile on here.
The first physical prototype was assembled at the beginning of January 2020. It consisted of a backplane-style motherboard with cards for graphics, audio, and input. It used jumper wires to connect the selection outputs of the address decoder to each addon card, to maximize modularity. Overall the first prototype was good for proving initial design ideas and discovering the problems with my design. However, it was also quite fragile and unreliable.
Currently I am working with the second physical prototype, which trades much of the modularity for reliability and ease of inspection. The selection signals have been moved to PCB traces, while the graphics and audio board now use dedicated connectors. The boards are also arranged flat instead of at a right angle to the motherboard, for easier access with oscilloscope probes.
The primary remaining hardware issues are as folllows:
- The blitter has a glitch when the draw rectangle starts at an X coordinate ending in ****1111
- The digital potentiometers used for audio volume controls have been discontinued during the development of the project