Building the Tynemouth Mini PET
Ultimate Commodore Charset / PETSCII / Keyboard Reference
Another addition to the The Ultimate C64 Reference: We’re adding character sets, PETSCII codes and keyboard layouts – supporting eight different Commodore computers.
Ultimate C64 KERNAL API Reference
The Ultimate C64 Reference is growing again: This time, we’re adding the KERNAL API reference – as always, in eleven different versions side-by-side.
Ultimate C64 Memory Map
The system software of the Commodore 64 has been extensively reverse-engineered. Next to disassemblies of the ROM, several “memory maps” have been published: tables that document system variables in the first kilobyte of RAM, and how to tweak the system software with PEEK and POKE. Now, I’m presenting the Ultimate C64 Memory Map: A C64 memory reference that shows eight sources side-by-side.
Typos in the C64 Programmer’s Reference Guide: C3PO or C3P0?
The Commodore 64 Programmer’s Reference Guide contains a memory map with a complete description of the zeropage and system variables used by KERNAL and BASIC, but now that we have the original source, we know there are three typos in this table.
Commander X16: Philosophy and Specification
I recently got involved in the Commander X16 project. I would like to give an overview of the project and the vision behind it from my perspective.
NES and SNES Controllers on a 6502 (like the C64)
NES and SNES controllers support 8 to 12 buttons with only three data pins (plus VCC/GND). Let’s attach them to a C64 – or any 6502-based system!
More Original Commodore Source Code
There have been a few new interesting additions to the Commodore Source Code repository, including:
Boxed MOS 6502 CPU
Back in 1975, you could order a boxed 6502 CPU directly from MOS in Norristown, PA. Here are some high-res photos of such a box and its contents.
Illegal Opcode Support for the Final Cartridge III Monitor
The monitor built into the Final Cartridge III is one of the best ones for the C64. Some of its unique features are:
Das Maschinensprache-Buch zum Commodore 64 [PDF]
Building and Hacking on the C64 KERNAL & BASIC with Modern Tools
The original Commodore 64 KERNAL and BASIC source code has been available for a while. It used to be built using Commodore’s assembler of a PET.
Reading the Raw Bits of a C64/1541 Disk without a Parallel Cable
An unmodified Commodore 1541 disk drive cannot transfer the raw bits of a whole track to the computer it is attached to: The Commodore Serial Bus is too slow to transmit the data in real time as it arrives from the read head, and the drive only has 2 KB of RAM, which is not enough to buffer the 8 KB of a whole track.
Ultimate Commodore 64 BASIC & KERNAL ROM Disassembly
My side-by-side C64 ROM disassembly/commentary page has been completely redone!
Building the Commodore TED Kernal with Modern Tools
The original Commodore TED (C16, C116, Plus/4) source code has recently appeared on zimmers.net. It is also available in my Commodore Source Code git repository.
Building the Original Commodore 1541 DOS Source
You might think the DOS ROM of the Commodore 1541 disk drive has been analyzed to death. But here are two new resources:
Analyzing the ROMs of Third Party Disk Drives for the C64
Most Commodore 64 users had a 1541 disk drives, but there were always also third part options. Most of them claimed full 1541 compatibility, which sounds impossible without using the same ROM. Let’s analyze the ROMs of some third party drives!
Original Commodore Source Code Collection
Over the years, the ROM source code of many Commodore computers and peripherals has appeared. I have been collecting them in a git repository here:
A Minimal C64 Datasette Program Loader
The Commodore Datasette recording format is heavily optimized for data safety and can compensate for many typical issues of cassette tape, like incorrect speed, inconsistent speed (wow/flutter), and small as well as longer dropouts. This makes the format more complex and way less efficient than, for example, “Turbo Tape” or all other custom formats used by commercial games. Let’s explore the format by writing a minimal tape loader for the C64, optimized for size, which can decode correct tapes, but does not support error correction.
Commodore 64 BASIC inside your USB Connector
Tomu is a super cheap Open Source Hardware 24 MHz ARM computer with 8 KB of RAM and 64 KB of ROM that fits into your USB connector! Of course I had to put Commodore 64 BASIC on it, which can be accessed through the USB-Serial port exposed by the device.