Optimizing a simple counting loop on the 6502, progressing from slow BASIC to increasingly faster assembly implementations. A practical guide to 6502 optimization.

Understanding two’s complement: how computers represent negative numbers, why it simplifies hardware design, and how to work with signed integers in assembly and high-level languages.

Implementing the Rail Fence Cipher on the Commodore 64 and TI 99/4A. A fun transposition cipher for secret messages with kids.

Modern and retro mix

One of my favorite peices of retro clone hardware is Bob Corsham’s KIM-1 Clone. I’ve featured it many places like the 6502 speed series.

I have the latest model of this board, and he made an interesting design choice. It actually has an FTDI chip on board and you use that via USB to connect via a modern computer with an FTDI driver. This is very convenient for working with a modern computer, but then eliminates the ability to use a real serial port.