I was rather hoping that my long-winded series on fixing a 48K Spectrum had concluded with Part 8, but it turns out this Spectrum had one more surprise in store for me. Last month, I borrowed its keyboard whilst testing a new ROM image in my Harlequin. I tested it afterwards and it decided to fail with garbage on screen. This is symptomatic of lower RAM failure, so I quickly unplugged it, got my multimeter …
This mini project was a good opportunity for me to practice my soldering skills, as well as get my hands on a Spectrum 128K clone that I could use for various projects. I have enjoyed reading Chris Smith’s excellent articles on reverse engineering the ZX Spectrum ULA. The Harlequin is the physical embodiment of his work. The board comes in two variants; a 48K version (currently on revision G), and a 128K version (on revision …
The Spectrum screen handling is not the most straightforward and, with lack of hardware sprites, scrolling, and an awkward layout, can be intimidating at first. This post details how I managed to scroll a 24×24 character block of tiles on the Spectrum within one VBLANK interval. The scroll routine employs a number of tricks to achieve this by: Using the stack pointer (SP) to fetch tile data and push it to the screen. Using self-modifying …
