Bank Switching Cartridges

Cartridges for the C64 provide either 8K or 16K of ROM that will replace parts of the memory visible to the CPU when plugged into the expansion port. Either 8K or 16K, that is all the Commodore can see directly on a cartridge. Then there is an auto-start mechanism implemented in the Kernal that can be triggered to execute code contained in that ROM when the machine is powered on or reset. Jani features an excellent article about how to create such simple cartridges on his site which I have linked to before.

A simple ROM cartridge: the OpenC64Cart.

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The XCPLA – Yet Another PLA Replacement

I’ve covered the PLA and the question how to replace a broken one before. First, when I repaired one of my C64 from back in the day, needed a quick replacement, and used an EEPROM on a simple adapter board. In a follow-up post I used a simple circuit suggested in a talk by Eslapion to test this PLA replacement for glitches and found plenty. Last but not least, I created a replica of the Super Zaxxon cartridge also to be used for testing the PLA. There is a lot more information online on this topic like the excellent Post on Breadbox64.

The broken PLA from a C64 mainboard.

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The NeoRAM Remix

A quick market survey on RAM expansions for the C64

The Commodore 64 features a whopping 64kB of RAM, hence its name. Most of this is actually usable at least when programming in assembler. While this used to be quite a lot when compared to competitors in the market, even back in the day there were different external RAM extensions. Some of the popular “freezer” cartridges like later versions of the Action Replay or the Super Snapshot feature some additional RAM of their own.

Commodore 1764 REU. (photo by T. Conté)

Commodore started selling their RAM Expansion Units (REU) in 1985 when the C128 came out. The REU was actually quite sophisticated, with its own controller — the MOS8726, REC — that provides fast memory-transfer by DMA.

The GeoRAM cartridge. (photo by T. Conté)

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On Kernal Switchers

The Kernal is the low-level “operating system” of the Commodore 64. The functions it provides are the basis for higher level routines in Basic and most other software running on Commodore’s 8-bit machines. In case of the C64 it comes in the form of an 8k ROM chip or as part of a 16k ROM chip in later versions. So the good news is, the Kernal is immune to corruption though any kind of malware. The bad news is, there is no easy way of updating or replacing it although Commodore’s original Kernal leaves a lot of room for improvement.

Kernal ROM from a C64.

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News Bits: Awards, Revisions, and Cases

An Award Winning Board

Today, I’d like to share some brief news and updates on multiple topics. First up is some exciting news. Last year, when I created and shared the Pi1541io layout I had those boards made by PCBWay and I entered their 2nd annual design contest on a whim with the popular revision 4 of the Pi1541io. And what do you know? Shortly before Christmas, I received an email from Eric of PCBWay who is letting me know that my board actually won first price in the category Most Popular Designs! Continue reading

Super Zaxxon Replica

A while back — following the repair of a C64 — I posted about testing the PLA replacement that I had used. In the great video on that topic shared by MindFlareRetro, Eslapion mentions two possible tests for a PLA replacement. One of these I covered in my post back then. The other test involves using a Super Zaxxon game cartridge.

Due to the unique way of bank switching implemented by that module, it seems to be particularly vulnerable to glitches produced by PLA replacements. Less-than-perfect replacements tend to produce crashes or skewed graphics when running that game. Continue reading

SD2IECplug v2.0

Last year I created my own rendition of the SD2IEC, dubbed the SD2IEC Pluggable. Version 1.0 left some room for improvement and recently I found the time to take on a new revision. Version 2.0 is even closer related to the design published by Shadowolf while maintaining the “pluggable” layout with the pass-through tape connector.

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The 32-Bit Tapecart

A few weeks ago, I built the through-hole version of the Tapecart based on an ATtiny44. The original and probably the most wide spread variant of the Tapecart is much smaller though. It is built from surface mount components and it is based on the much harder to get 32-bit AT SAM D09 controller.

I wanted some of those Tapecarts in my collection so I had “a few” boards made, ordered the components including a matching case and waited for everything to arrive. Soldering the SMD version is not hard, the smallest components have a 0805 footprint. Continue reading

TapecartFlasher Nano

In my previous post I introduced the Tapecart, a thumb drive for the Commodore 64, and built one of those. The only major issue with these great devices is the 1.5 hours it takes for the C64 to transfer the 2 MB of data to them.

Fortunately, Detlef Gerhardt came up with the idea of hooking up the Tapecart to an Arduino in order to transfer the data using a modern PC. It turns out, this speeds up the transfer considerably and it also eliminates the need for copying TCRT images using a SD2IEC or similar device. An early version of Detlef’s TapecartFlasher software is available on Github.

Tapecart and the Arduino. Ignore all the other components for now.

The original setup for the TapecartFlasher is as simple as it gets: simply hook up 5V and GND from the Arduino, then connect the 4 remaining lines of the cassette port interface to D2-D5. I tried this on a breadboard first and it worked out of the box! The most complicated part here was the lack of a proper connector, so I just soldered leads to the Tapecart module. Continue reading

The Tapecart – A Thumb Drive for the C64

The Tapecart is a relatively new piece of hardware that was devised for the Commodore 64 by Unseen and enthusi  and introduced in late 2016. The general idea is quite compelling: The small module features 2 MB of serial flash memory and plugs into the cassette port of the Commodore. By just entering LOAD or the “Shift+Run/Stop” shortcut, a small bootstrap program is run that will then very quickly load up to 64 KB from the Tapecart into the C64 for execution. No cable and no external power supply is required and important other ports remain unused. This is probably as close to a “thumb drive” for the old hardware as it gets.

Both the software and the hardware of the Tapecart are available under an open source license. The hardware is very cost optimized and can be built for only a few € or $. Continue reading