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Compare chip minutiae
Spent some time this evening playing with the compare chip (315-5250) on my E-Swat board. This chip is present on several System 16B boards as well as on the X-board systems, and is used for doing simple 16-bit compares between values. Well, at least it looks simple at the start. For the most part, the implementation I currently have works fine, but it's not good enough to get the remaining few protected Golden Axe sets working. The symptom is that your player is stuck near the top of the screen.
Fiddling tonight revealed a few small details were wrong, but nothing to solve the overall problem. I'll next need to modify my "trojan" program to let you edit the input parameters more flexibly, so that I can try some real values from the PCB.
I also began writing some test code for System 18 that will verify the off-by-one column scroll bug that I am deducing is present on the real hardware. If it's not, then I'm completely at a loss to explain why D.D. Crew leaves a pixel of garbage behind during the scrolling on the attract mode.