Damien Guard • 5/31/2026

VTX5000: Part 5 - Rendering

This article, part 5 of the VTX5000 series, explains the rendering process for Viewdata 40x24 frames on a ZX Spectrum's 32x40 display. It covers control codes (e.g., cursor movement, clear screen), the ESC mechanism for color/attribute changes, cursor bounds-checking with wrapping, and the display buffer storage (960 bytes). It also describes the CALC_BUF_ADDR routine for converting row/column to buffer address using Z80 assembly, and mentions the font derived from the Mullard SAA5050. Targeted at retro computing and Z80 programming enthusiasts.

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#rendering #assembly #Viewdata