UPDATES

10/12/09: Moved the common area of RAM to a separate pair of 8KB chips, instead of the top 16KB of the main 128KB RAM. This gives us a little extra memory, prevents programs from accidentally overwriting things in the common area by setting the banking register too high, and (more importantly) simplifies the memory-mapper logic.

10/02/09: I've been considering how to accomplish baud-rate generation for the serial ports almost since the beginning of the project. It looked like it was going to require a binary counter and a clock speed that was a power-of-two multiple of a common baud rate. Today I realized that I've actually had the answer all along with the Z80 ACTC timer chip, since the timers generate an external pulse when they finish their count and reset, which I can use as the baud clock for the DART. I checked the datasheet, and sure enough, this was actually one of the suggested applications. ...maybe I should read manuals more often.

10/01/09: Put together a basic list of BIOS calls.

09/30/09: I think I've got most of the address decoding/memory mapping circuitry designed, as detailed on the Design page. Now I need to figure out either how to use xfig or how to draw decent symbols in TinyCAD...

Funny story! The 65C02 I bought? Turned out to be a Motorola audio part with the same number. Oh well, I did find a site where I can get a real 65C02, as well as a number of other parts I need.

09/21/09: Site goes up! Hopefully this should both keep me motivated and help me get in touch with people who know the answers to the things I can't figure out on my own. We'll see!

09/18/09: Added a secondary bank-selector for the zero page and stack, to make it easier to have programs larger than 32KB.

09/15/09: I finally bit the bullet and bought a 65C02. I'd been hoping to use my original 6502, but the combined allure of a 5MHz-rated CPU and those handy extra instructions was just too much to resist. This also meant I had to ditch the 6526 CIA, which is only rated for 1MHz; I suppose I could've used a clock-divider or somesuch, but that kind of thing is a little beyond the scope of this project. Instead, I'm going to use a Z80 ACTC for timer purposes, which is rated for 4MHz. It doesn't have the 6526's I/O ports or shift register, but I didn't have any plans for those anyway. Plenty good enough.