In this episode of our tour through the 8086 assembly language, we learn a few new opcodes and concepts CBW makes an appearance, as does the powerful XLAT for looking up values in … look-up tables! We use this to make a text mode plasma like effect. It is a bit simpler compared to what we did in another episode on the VGA card, but this time the executable is tiny, coming in at less than 170 bytes. We talk a bit about how to access screen memory in text mode and how to query the real time clock in the PC.
There are many diagnostic cartridges for the C64 which can help troubleshoot problems with broken or dead C64s. This new cartridge comes with three special features: it measures the 5V rail, which can cause problems with the machine, it shows the CPU clock, which can be the cause for black screens, if absent, and it can run three different diagnostic ROMs. The C64 Deadtest, C64 Diag and C128 Diag are selectable via a small switch. Let’s assemble this new troubleshooting tool and test it out!