2600 programming is an exercise in crazy. - The parallel port chip has direction bits that control whether a line is an input or an output. This register is re

2600 programming is an exercise in crazy. - The parallel port chip has direction bits that control whether a line is an input or an output. This register is read/write, so you can use it as temporary memory when you don't care about reading or writing I/O (which is most of the time). - Lots of code doesn't need a stack; it doesn't call anything, and it can just jump to where it needs to be at the end. Now we can use the S register for something else. Many, many other tricks. I used some of them a few years ago on an embedded system that needed to fit into 1920 bytes. I enlisted a cow-orker into the effort and we were both cackling away. [Later, the hardware guys offered us a different chip with twice the memory, but at that point we were too close to shipping to make any changes, and besides, it wouldn't have been as fun... :-) ]