How 80s BASIC actually knows what you're typing (visually explained)

In this video, a visual guide to exactly how the TRS-80 Color Computer and Dragon Computer read their keyboards. Using a routine in their ROM that today we'd probably call a "driver", they directly control hardware that sends signals through columns of the keyboard's matrix, and reads resulting signals that exit the rows. They employ clever tricks to deal with human reaction times, unstable switch connections under the keys, and an odd hardware choice to reuse keyboard signal paths for the joystick buttons. Also, a detailed accounting of all the ways Dragon's routine improved on the CoCo's, including a new optimization, and a new feature: auto-repeat! Keyboard matrix & assmebly code deep-dive:    • Deep dive into keyboard access (and joysti...   CoCo's flood-fill algorithm:    • Retro graphics GENIUS revealed!  Inside 19...   Other materials used in this video: Unraveled disassembly of CoCo's ROM: https://colorcomputerarchive.com/sear... Dragon ROM source: https://github.com/davidlinsley/Drago... Footage of CoCo keyboard disassembly:    / @canadianretrothings   Bouncy Switch voltage graph: https://commons.wikimedia.org/wiki/Fi... Stylistic deboucing pic: https://typetest.io/blog/posts/2026-0... Dragon 64 picture: https://commons.wikimedia.org/wiki/Fi... XRoar emulator: https://www.6809.org.uk/xroar/ 00:00 Intro 01:47 Hardware strobes 02:59 Dedupe 04:45 ASCII Conversion 05:48 Debounce & joystick buttons 10:53 Caps lock 11:18 Dragon