Articles

The Videx VideoTerm was the 80-column card that turned the Apple II into a business machine. Emulating it on an FPGA means reverse-engineering a 1981 MC6845 CRTC design and understanding why slot 3 is unlike every other slot in the machine.

Getting 80 columns of text from VRAM to pixels on a modern HDMI display: the Videx VideoTerm rendering pipeline in SystemVerilog, C8-space ownership, and the Pascal boot hang that required reading a 1983 firmware disassembly to fix.

The ThunderClock Plus is the only Apple II clock card with a built-in ProDOS driver. Emulating it means implementing a NEC uPD1990AC serial calendar clock in SystemVerilog — and exploiting a USB-C power trick to give the FPGA battery-like time persistence.

Adding a second expansion-ROM-capable card to the A2FPGA exposed five latent bugs in the upstream codebase — bugs that had been present for approximately two years and went undetected because only one emulated card had ever used C8-space at the same time.

Smalltalk-80's object model is the most consistent in computing history. Understanding it — metaclasses, live images, and all — is the first step toward building one from scratch.

To build a Smalltalk-80 VM you need a compiler. But Smalltalk bytecode is useless without a running Smalltalk. The escape: a JSON intermediate representation and an empirically-discovered grammar.

The cold-start loader reads a JSON description of every Smalltalk class and builds a complete, correctly-linked heap from scratch. The garbage collector tells you when you got it wrong.

The Smalltalk-80 bytecode interpreter: execution contexts, method lookup through the metaclass chain, non-local block returns, and the BlockClosure bug that took weeks to find.

The Smalltalk-80 file-out is not a complete description of a running system. Some globals only ever existed interactively — they're not in any source file, but the code that uses them was written assuming they exist.

Getting a Smalltalk-80 system to display something requires implementing BitBlt, the 1980 graphics primitive at the foundation of everything visible. Then saving the live heap so you never have to do cold start again.

The decision to replace Smalltalk-80's 1980 display model with GPU-accelerated rendering: deleting Form, BitBlt, and Pen from the codebase and building Wise Owl Smalltalk on SDL2 and SkiaSharp.

How the Disk II's radical hardware design made Apple II copy protection possible — and what a flux-level disk image reveals about a 1981 floppy that defeated nearly every copy tool of its era.

Disassembling the Apple Panic boot loader reveals self-modifying code, a mathematically elegant GCR table corruption, a custom post-decode permutation, and a per-track marker scheme that makes the disk illegible unless you already know the key.

Sector 1 fails its checksum every time. Three theories, each plausible, each wrong. The real cause turns out to be a fundamental property of how WOZ files represent circular disk tracks — and it was in our own bit-stream reader the whole time.

What a recursive-descent disassembler finds in 27KB of 1981 Apple II game code: an XOR sprite engine, speaker timing loops, enemy AI state machines with three behavioral trees, BCD scoring, 104 subroutines, and a memory layout where every byte has a reason.

Every nibbler command demonstrated against Apple Panic — actual outputs, what each line means, and how to read the results. The reference guide for analysing a copy-protected Apple II WOZ disk image from first scan to disassembled source.