Thursday, October 20, 2016

Considerations on the Apple-1 system

Originally the Apple-1 computer was planned to have a Motorola 6800 CPU, cheaper than a more popular Intel 8080 (400$ in those ages). So the project has never been developed, and remained on paper. It was modified to have a cheaper and better configurable 6502 ($25), just released in those ages.

So the Apple-1 was designed around this processor, equipped with RAM; a ROM containing the little operating system that Wozniak developed on purpose; a ROM containing the information on the character set for the video section; the hardware video terminal section; and a programmable input output interface chip.

Actually the computer is very simple compared to what we are used nowadays, but Mr. Wozniak was really smart in putting everything together. Especially the video terminal section is really clever because it is an assembly of logic ports and electronic components that are able to generate an NTSC composite video signal without a specific IC like modern video cards.

For my project the design is "easier" because I have to program everything software side, the tricky part is to emulate as best as possible timings and behaviour of the virtual hardware (CPU, I/O, Video signal etc.).