antforth

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Ant Skelton

22 Apr 2026 — 1 min read

It's all been a bit "jazz improv" recently as we fought to get ourselves to 100% coverage of z80 opcodes. Hopefully we are now back on track as we queue up /bmad-bmm-create-story 5.1 - finally, the elusive comments!

We kick off development with /bmad-bmm-dev-story 5.1 - this should be short and sweet. Astonishingly code review finds a register clobbering issue, but it is quickly fixed.

strings.asm

/ is pretty basic:

It just sets the current Text Input Buffer pointer to the end, so there's nothing left to parse.

( is slightly more elaborate, as it has to scan forwards to find a matching ')' -- here's the relevant part:

Testing

Continue reading: MARKER snapshot and restore

Adventures with Cowgol

I've written two languages so far for the MicroBeast: AntForth, which I use heavily every day for experimentation, and another Lua-like language which is part of a super-secret future project that is still under wraps. But I'm always on the lookout for new projects, and fancied

Testing the Kempston compatible joystick interface

In part 2 we built our interface hardware, now it's time to try to read it from the MicroBeast! To do that, we'll have to actually connect it to a MicroBeast, so we'd better clear up the support circuitry we've been using

Making a Kempston compatible joystick interface

In this post, we'll make our own version of the Kempston joystick interface that I described in part 1. We'll make a slight modification: full address decoding, to avoid any future resource conflicts. We'll keep the 74HC138N (3-to-8 decoder) for decoding the control signals,

The Kempston joystick interface

In the 80s, everyone who was a serious ZX Spectrum nerd had the Kempston joystick interface. If you were unfortunate enough that your parents bought you some Protek, DK'Tronix or (horrors!) Interface II nonsense, you kept quiet about it: that kind of gear would get you laughed off