ROL 00000000 – READY

Like many people my age, my first exposure to a personal computer was a 6502-based system. In my case, it was an Atari 400, paired with a BASIC cartridge. There are a few people on the internet with series about building a retro computer using a 6502 and a handful of other chips. I’ve decided to jump onto the nostalgia bandwagon myself. I’m a software engineer by profession and wanted a hobby that wasn’t also software engineering! So, at the ripe old age of 50-something, I decided to take up electronics.

My goal for this particular project is pretty simple: A straightforward 6502-based computer. I am going to have 32K of RAM, 8K of system ROM, 8K of “application” ROM, a “good number” of GPIOs and serial I/O for communication with the user. So, initially, no keyboard or graphics or character output. Nothing fancy, just serial. The two 8K ROMS will be setup such that the first ROM will be permanent and contain system interface routines—essentially a BIOS like in an old 8086. The second ROM will contain the application to run: it could be a game, a monitor, a simple O/S, a BASIC interpreter or an Assembler and will be removable, like the cartridges for the old 8-bit Ataris. Later, I may get more adventurous and implement some sort of graphics system, keyboard (or general USB) interface.

I decided on the name, “ROL”, which comes from the 6502 instruction set: ROL rotates a byte one bit to the left. This is the same as multiplying by 2. I also like the way it rolls off the tongue!

As the project progresses, I will document it here. Since it’s a relatively simple project, it should be a short series. I will update this post with links to each segment as I complete it:

Check out as a good starting point for 6502 hardware design. It has good forums and links to several 6502 projects around the internet.