Dan’s MEGA65 Digest Podcast Dan Sanderson

The Summer of MEGA65 begins! The latest delivery batch is in progress, and many preorder holders are receiving their new favorite computer.
If you’re new to this Digest, welcome! Here you’ll find news about the MEGA65 and community projects, and interactive feature articles of things you can try for yourself. Read the Digest while next to your MEGA65 and PC for the best experience.
Also, every Digest has a read-aloud audio edition. Click the audio player at the top of the email or website, or subscribe to “Dan’s MEGA65 Digest” in your podcast player. I don’t know how many people listen to it, but I enjoy making it.
In this Digest, we’ll start taking a look at the MEGA65 KERNAL, the main operating system of the computer. We’ll build off of last month’s discussion of interrupts and the CPU memory map, and try writing a MEGA65 version of a classic KERNAL extension: a desktop time-of-day clock.
Let’s get started!
Batch #3 is arriving!
MEGA65 home computers are now arriving with their new owners! Trenz Electronic has begun sending out the third manufacturing batch, and will continue to fulfill pre-orders steadily. Congrats and welcome to everyone receiving a new bundle of joy!
Back in January, we were able to confirm with Trenz that this manufacturing batch will be large enough to cover all preorders placed up to that point. I continue to use that as a conservative estimate. New preorders placed in the last few months may need to wait a bit longer—or maybe not. For all we know, Trenz may be able to make quick work of another batch and get everyone taken care of. Rest assured that everyone involved in this project wants you to have a MEGA65 as soon as possible.
Of course, you can still order the MEGA65 if you haven’t already. Tell your friends!
MEGA65 at the Pacific Commodore Expo Northwest, June 22-23, 2024
If you’re near Seattle, Washington, USA this month, I will be presenting the MEGA65 at the Pacific Commodore Expo Northwest, June 22-23, 2024. Admission is free. The space is cozy and filled with Commodores, and this year we have access to additional space for presentations. I’ll have my MEGA65 at a table all weekend for people to try.
I gave a talk on the MEGA65 at last year’s PaCommEx NW that went reasonably well, despite being hastily planned. Here’s hoping that I’ll have this year’s talk figured out in time. 😬
MEGA65 at the Vintage Computer Festival Midwest, September 7-8, 2024
I’m working up plans to be at the Vintage Computer Festival Midwest, September 7-8, 2024, at the Schaumburg Convention Center in Schaumburg, Illinois near Chicago. This large show attracts enthusiasts from all over the USA and Canada, and is a regular pilgrimage for collectors, computer clubs, YouTubers, and makers of modern retro computers and peripherals. Admission is free.
This year, I’ll be collaborating with Jim Happel (jim_64) on a MEGA65 table. I’ve also applied for a speaking slot, though those won’t be announced until next month, so, fingers crossed. 🤞
MEGA65 at the Portland Retro Gaming Expo, September 27-29, 2024
My MEGA65 and I will be at the Portland Retro Gaming Expo, September 27-29, 2024, in Portland, Oregon, USA. PRGE is one of the largest vintage video gaming shows in the Pacific Northwest, and this year they’re doing a home computing exhibition. Come for the interactive volunteer-run computer exhibits, then stay for the weekend of talks, playable arcade games, and the vendor floor. I’m not doing a talk at this one, but I’ll have my own table in the home computing area.
PRGE is a ticketed event at the Oregon Convention Center. If you’re visiting from out of town, get your hotel rooms reserved early—and make sure to leave time to explore Portland!
Lala The Magical (preview)
Majikeyric is previewing a new game for the MEGA65! Lala the Magical (preview) is an adorable puzzle platformer, with parallax scrolling areas and tons of enemies and collectibles. It’s based on t

At least once before in this Digest I’ve said something about how there’s a way to write a program to perform precisely timed actions, but the actual technique would have to wait until a future issue. In this issue, we’ll start looking into this, with a focus on synchronizing a program with a particularly useful hardware feature: the raster beam.
To do this effectively, we’ll introduce an important programming paradigm supported directly by a feature of the CPU, called interrupts. To get that to work, we’ll also take a brief look at how to uninstall the KERNAL operating system by changing the system’s memory map.
Any news?
Trenz Electronic is busily assembling new MEGA65s, still on track for delivering the next batch in the next few weeks. The Discord and Forum64 board have been quieter than usual, with everyone starting new projects or resting up from previous ones. I can’t wait for the rush of new people joining and asking questions!
If you have a project in progress that you’d like to see featured in the Digest, let me know! You can also announce your project in the #announcements channel on the Discord, and upload your work in progress to Filehost for others to try. Beginners welcome! Some of the coolest stuff we’ve seen for the MEGA65 has been written in BASIC by people like you just trying things out.
The time keepers
Every computer contains a component that generates a clock signal, a fast and precisely timed electronic pulse that drives the digital devices in the computer. Like turning the crank of a music box, these pulses advance the internal mechanisms of each device through their various stages to perform computations, and to generate signals of their own. The clock signal also synchronizes the devices with each other, so they can communicate with one another over their electronic connections.
MEGA65 programs can take advantage of three specific devices driven by the system clock to execute code with precise timing: the CPU, the VIC video chip, and the CIA chip.
The CPU
The CPU uses the clock signal to perform the machine code instructions of a program. Each instruction requires a certain number of cycles to perform, where each cycle takes a fixed amount of time based on the clock. For example, the lda #$ff instruction, which loads the byte value $ff from the program code into the accumulator register, takes two CPU cycles to complete. The cycle cost of an instruction depends on the instruction and addressing mode, but it’s typically between 1 and 6 cycles, and as many as 14 cycles for fancier operations like the 45GS02 Q-register instructions.
In its default MEGA65 mode, the MEGA65 CPU performs instructions at 40.5 million cycles per second, or 40.5 megahertz (MHz). The MEGA65 can also underclock its cycle rate to emulate a Commodore 64 (1 MHz), Commodore 128 (2 MHz), or Commodore 65 (3.5 MHz).
In theory, you can analyze the duration of a section of machine code by looking up the cycle costs of each instruction and adding them together. Commodore 64 programmers sometimes do this to optimize small sections of code, especially for advanced video effects that require precise coordination between the 1 MHz CPU and the VIC video chip. This is less necessary with the MEGA65’s 40.5 MHz CPU, which outpaces most of the signal frequencies that a program might care about.
A program can pause for a period of time by executing instructions and ignoring the results, simply to burn through cycles. This could be a series of instructions in memory, a loop with a counter, or a loop that exits when a hardware register changes. This technique is known as busy-waiting because the CPU can’t stop executing instructions: it has to twiddle its thumbs to keep busy—and also to figure out when to stop waiting and continue the program.
Try these examples of busy-waiting in BASIC:
5 REM -- PAUSE BRIEFLY BY DOING NOTHING IN A LOOP
10 BORDER 0
20 FOR A=1 TO 20000
30 NEXT A
40 BORDER 1

5 REM -- WAIT FOR JOYSTICK FIRE

[Did you know: All issues of the Digest have an audio version! Search for “Dan’s MEGA65 Digest” in your favorite podcast app, or check out the audio player at the top of each issue. — Dan]
There are two methods for making sound and music with the MEGA65, as it is currently implemented. The first method is the four SID chips, programmable devices that generate waveforms with requested parameters using analog electronic components. We took a dive into the SID chips back in—November 2022?? How long have I been doing this?? …
The MEGA65 can produce sound another way. Pulse-Code Modulation (PCM) describes a waveform as a sequence of values over time, literally the shape of the desired waveform as a series of high and low numbers, as if drawn on a graph. The computer feeds these numbers into a device called a Digital-Analog Converter (DAC) that produces the waveform in that shape, as if rapidly changing the position of a speaker membrane according to each value. The MEGA65 has four DACs, and these waveforms are mixed with the rest of the audio system to produce the stereo audio output of the computer.
With PCM, a computer can reproduce real-world sounds captured by a microphone, such as human speech or musical instruments. Today, we take this extremely for granted: modern computers generate pretty much all sound using PCM waveforms. We used to call this “digitized sound,” in contrast with “synthesized sound.” Now we just call it “sound.” While PCM gives a computer program much more control over the generated sound, the trade-off is memory: relative to the memory sizes of 1980’s computers, PCM sound data takes a huge amount of space, depending on the length and quality of the sounds.
In this issue, we’ll look at how to control the MEGA65’s DACs to play digitized sound, as well as techniques for wrangling sound data for use in your programs. As usual, we’ll spend a bit too much time nerding out on theory and file formats.
Are you ready? Here we go.
Featured Files
Bomb’em All by btoschi, an explosive action game for two to four players. Drop bombs, pick up items, and break through walls while trying to trap your opponents in the blast zone. The game supports the Four Fun joystick adapter for four joysticks, or can be played with a mix of joystick and keyboard controls.
BASIC Star Galactica by jim_64, a space battle adventure. Destroy the Cylons and protect the fleet—and the future of humanity. Don’t miss the downloadable, printable disk label and manual.
fredrikr has prepared the fourth in his series of text adventure game bundles for the MEGA65, featuring modern classics from the interactive fiction community. This pack includes a variety of games released from 1995 to 2023, all playable on the MEGA65 thanks to the Ozmoo Z-machine player. (See the Digest from October 2022 for more on Ozmoo and MEGA65 adventure gaming.)
Another arcade core from muse! In Ghosts’n Goblins (1985), you are brave knight Sir Arthur, on a quest to save the Princess Prin-Prin. Don your armor—and take care not to lose it—while fighting waves of zombies, giants, demons, and other monsters. This classic from Capcom is considered one of the best video games of all time—and one of the most difficult. As with the other arcade cores, you will need to find the game ROM online, and follow the instructions to install it.
In Stranded, a graphical adventure game by Magnus Heidenborn, your boat has crashed and washed ashore a deserted island. Magnus wrote Stranded for the Commodore 64, specifically the modern TheC64 clone. Gurce ported it to the MEGA65, and added original music. I especially appreciate the novel keyboard-based linear travel and exploration mechanic, which works around common issues with point-and-click adventure games. Check it out!
Expansion board progress
Paul is making progress on the MEGA65 expansion board project. As we reviewed in a previous issue, this project intends to produce an internal hardware e

Spaceships. Aliens. Marios. Goombas. Bullets. Fireballs. Mouse pointers, text cursors. Any of these could be a sprite, a feature of a computer graphics system dedicated to things that move. The sprite capabilities of the Commodore 64’s VIC-II chip super-charged video games and user interfaces beyond a single screenful of character text or a bitmap image. The MEGA65 includes support for VIC-II hardware sprites, and has sprite-related BASIC commands that make them easy to use in your programs.
In this Digest, we’ll review the VIC-II sprite system’s capabilities, try out the sprite features added to Commodore BASIC for the C128, C65, and MEGA65, and step through a development workflow for using sprites in BASIC games. And we’ll try putting these pieces together to make a simple arcade game.
But first…
The User’s Guide, 2nd edition, now available
You can now buy a spiral-bound printed copy of the MEGA65 User’s Guide, 2nd edition!
This new edition has been updated substantially from the 1st edition printing from two years ago. It covers the upcoming v0.96 release, with instructions for new features like Ethernet file transfer, and revised information on important topics like upgrading the firmware and using disks. The BASIC reference has been updated with corrections, polish, and material on new features. And there are handy new appendices on screen codes and system colors.
Whether you have the 1st edition and want to upgrade, or don’t yet have a MEGA65 and just want a useful book to go with Xemu, getting the 2nd edition in print is a great way to enhance your MEGA65 experience.
I wrote a FAQ with more information, including what’s happening with the manuals bundled with new MEGA65s. Let me know if you have any questions.
Release testing update
The v0.96 release package has been in public testing for a month, and we’ve been chasing down issues and polishing it up for factory installation on all of the new MEGA65s. This process should be complete a week or so after you read this. Many thanks to everyone who has contributed to the testing effort!
What happens next: the v0.96 release package will be made official and sent to Trenz for the factory installation on new machines. It will be declared the new stable release for R3A and R6 mainboards, and made available on Filehost. Everyone with the “retail” MEGA65 will be encouraged to upgrade.
DevKit and Nexys board owners will need to wait, just a bit. In order to meet the assembly schedule, we have had to defer preparing new cores for these boards until after this release. The plan is to immediately start work on these deferred tasks, and issue a v0.97 update within a couple of months that includes support for these boards. You’re always welcome to help test along the way, just be aware of known issues with slot 0 flashing on the older boards.
Upgrade party at lydon’s place! 🎉
New Intro Disks!
Gurce has put a ton of work into preparing the new software bundle for the SD card that will ship with the new MEGAs. Current owners are familiar with the “Intro Disk” menu that starts when you first switch on the computer, as well as other bonus goodies that come on the pre-installed memory card. The new bundle includes all of that and much more, a total of 191 (one hundred and ninety one!) menu entries. And that’s not even counting the disk menus themselves, with useful information and musical accompaniment. This compilation starts all new MEGA65 owners off with plenty to do on their first day. Huge thanks to Gurce for his meticulous work on this project, and of course to everyone who has written software for the MEGA65.
You can download the new software bundle on Filehost. (There’s a separate download for registered owners with a more complete version of GEOS.) If you don’t yet have a MEGA65, you can try it out in Xemu—or save it as a surprise for when your MEGA65 arrives!
New on Filehost
Don’t miss these new titles on Filehost:
Rocket Delivery

It’s time! We have a shipping schedule for the next batch of MEGA65 computers, and a candidate for the next platform release. Everyone is invited to help with testing, so let’s get to it!
Shipping update!
Trenz Electronic has announced that the next batch of MEGA65 computers will ship on June 1st, 2024.
We currently expect that all preorders up to this point will be included in this batch. If you need to make adjustments to your preorder before then, contact sales@trenz-electronic.de.
Once we clear the preorders, remaining stock will become available for purchase in the Trenz Electronic store, while supplies last.
Please bear with us while we work through any last minute issues that might change these estimates. And thank you so much for your patience! I can’t wait for you to receive your MEGA65!
v0.96 release candidate now available to test!
To make the new delivery schedule, we need to hand over the gold masters of the next release of the MEGA65 firmware and system software, as well as the updated User’s Guide, to Trenz Electronic by January 31st. Release v0.96 of the firmware, ROM, and system software will be installed at the factory on all MEGA65s about to ship. Of course, it will also be available as a free upgrade for all existing MEGA65s. This next release has a ton of new features and bug fixes—and we need testers!
If you have a MEGA65, you can install the release candidate on your machine to help test. If you don’t have a MEGA65 yet, you can still help by testing the new version of the ROM with an updated version of the Xemu emulator.
Testing the release candidate on a MEGA65
To begin, be sure to back up your SD card, or use an alternate SD card, before proceeding with testing. I usually just move the SD card to my PC, then copy all of the files from the SD card into a folder on my desktop. This doesn’t back up the configuration or Freeze states, but personally I don't keep important freeze states around long term. Alternatively, you could also use a disk imaging utility to back up both the hidden configuration partition and the files partition.
If you’re using a fresh SD card for testing, remember to prepare the card first using the MEGA65’s SD Card Utility. Insert the card in your MEGA65, hold the Alt key while switching on the computer, then select the utility from the menu and follow the prompts. This erases all data on the card.
Here’s how to get the files for the release candidate:
* Release v0.96 RC core and system software. Select the latest build that begins with mega65r3-r-0.96, such as mega65r3-r-0.96-build-5.7z. The “r3” refers to all MEGA65s delivered up to this point. The MEGA65s shipping in June will be known as “r6.” Yes, we’re skipping R5 after all: we found one small non-electrical change needed for the board during R5 testing.
* Release v0.96 RC ROM. Sign in with your Filehost account with your owner code redeemed to access this. Download the most recent version: 920391.bin.
* MEGA65 command line tools: Windows, Mac, or Linux. These will be bundled with, and be the basis for, an upcoming version of the M65Connect app, and are generally useful on their own for the new Ethernet file transfer feature.
* The MEGA65 User’s Guide, 2nd edition (PDF).
Unpack the mega65r3-r-0.96-build-5.7z archive. Transfer the .cor file to the root of your SD card. Open the sdcard-files folder, and copy its contents (.M65 files) to the root of the SD card as well.
Rename 920391.bin to mega65.rom, and transfer it to the root of your SD card.
Install the SD card in your MEGA65. With the power switched off, hold No Scroll then switch on the computer. This opens the core selection menu. Hold the Ctrl key and press a number to select an appropriate core slot for the new core, then follow the prompts to select the .cor file and flash the core. See the User’s Guide for more information about upgrading cores.
Using both the release candidate and the previous stable release with one MEGA65
I re

Our robotfindskitten adventure continues! In part 1, we introduced the robotfindskitten experience, and described tools and techniques for building an rfk game in BASIC 65. In part 2, we started building a similar toolkit in assembly language, starting with KERNAL routines, memory access techniques, and screen memory registers. This month, we complete the toolkit, and I present my own attempt at an assembly language version of the game.
But first, a whole bunch of new stuff!
R5 main board in testing!
The new R5 main board test units have arrived and Paul has started the “bring-up” process, adapting the FPGA core to the design changes. With some minor corrections to the assembly, this should resemble the main boards that will ship with new MEGA65s going forward, including all pending pre-orders. Many thanks to Paul, Trenz Electronic, and the hardware testing team for the work they are doing.
Unicone, by deathy
deathy has another new game release! In Unicone, you are chasing a unicorn that poops ice cream. Move your ice cream cone left and right to catch falling ice cream scoops dropped by the unicorn. A fun game in the tradition of Kaboom! (or its lesser known ancestor, Avalanche), Unicone features high resolution graphics, sampled sounds, a wide variety of control schemes, and a unique ice cream balancing mechanic for extra challenge in later levels. Download Unicode from Filehost.
Want to see how it works? deathy has generously released the C source code to Unicone using an open source license, and the assets using a Creative Commons license. The code builds with the Calypsi C cross-compiler, a modern retro development suite by hth313 that recently added support for the MEGA65’s 45GS02 CPU. Check it out!
The Ghosts of Blackwood Manor, by Stefan Vogt
Stefan Vogt, the author of the adventure games Hibernated and The Curse of Rabenstein, has a new adventure out for multiple platforms including the MEGA65. The Ghosts of Blackwood Manor is an interactive horror game with three possible outcomes, and each outcome fills out the story.
And of course, Ghosts is getting another gorgeous boxed release from poly.play! Pre-order the boxed release, and get it digitally right now for a donation of your choice.
Gurce’s BASIC 65 Dev Vlogs
Gurce has been doing a series of live stream development vlogs coding a game from scratch in BASIC 65, using the Eleven programming environment. The game, currently titled “Way of the Imploding Foot” (or just “MegaFoot” for short), is a side-view fighting game, featuring low resolution block character graphics, animated fighting characters, and parallax scrolling.
You can start with episode 1, and subscribe to find out about new live streams. Also check out the Github repository for the game, or just try the latest D81 disk image. When browsing the repo, be sure to locate the .ELPC files (such as FOOT.ELPC), which contain the code in Eleven syntax viewable as a text file on a PC.
Gurce is welcoming contributions on this project! If you’d like to try implementing a feature in BASIC using Eleven, let Gurce know on the Discord.
Discord upgrade!
The MEGA65 Discord is the MEGA65 community’s real-time meeting spot, a great place to ask questions, show off your projects, and meet other MEGA65 enthusiasts. Thanks to MEGA65 Discord moderator KiDra, the Discord now has a fresh new structure and some really cool new features! Here are just a few highlights:
* New section layout. Channels and resources are now organized in sections based on how you engage with the project, such as regular use, programming, and platform development. Click or tap a section title to collapse sections you use less often.
* Discord forums. Sections now include Discord forums in addition to text chat channels. Forums are especially useful for asking technical questions: each question stays visible in a list, and answers and discussions stay organized by topic. Once you have the answer you need, you can close the discuss