The RAD Expansion Unit is a cartridge/expansion for the C64 and C128 using a Raspberry Pi 3A+, 3B+ or Zero 2 to implement the actual functionality. It emulates a RAM Expansion Unit up to 16mb (compatible to CBM 1700/1750/1764 REU, CLD Super 1750 Clone, CMD 1750/1750XL) and a GeoRAM/NeoRAM memory expansion up to 4mb. It also features a menu to browse, manage and launch REU- and GeoRAM-images, NUVIEs, PRGs and Vice Snapshots (VSF).

The RAD also supports an external disk drive and printer emulator, the IECBuddy, which is the result of a great cooperation with David Hansel. The IECBuddy can be used to synchronize files with the RAD and is integrated into its menu.

The RAD is designed to not only emulate existing extensions, other things that have already been tested (but not yet included here) are, for example, MOS 6510/8500 emulation (incl. turbo mode), using the RAD as a (co-)processor (in fact the menu runs on the ARM CPU only). With the RAD you can also play Doom on your C64/C128.

RAD's functionality is entirely defined by software. The connecting circuitry is quite simple and does not include any programmable ICs and is thus easy to build. It's a sibling of my other projects: Sidekick64, SIDKick pico and SIDKick.

The RAD has been tested with various PAL-machines (C64s, C128, C128D) and NTSC-C64s/C128s, as well as with the Ultimate64 (the inner workings of the Commodore 64 Ultimate). More in-depth tests with SX64 or C64 Reloaded boards remain to be carried out (not by me, I don't own such machines/devices, but the RAD was reported to work).

Using the RAD

Assuming you have your hardware ready and set up the SD card (see below for instructions), the RAD will boot the C64/C128 into its main menu unless configured to not do so. In the menu you can browse and select files:

Main menu

| key | command | |----------|:-------------| | H | display help | | cursor keys, F1/F3, HOME / DEL | navigate files / directories go to first entry, directory up | | RETURN | start PRG or select image, press 2x to autostart NUVIE or GeoRAM images | | S | mark or unmark a file for syncing (transfer to and from) the IECBuddy () | | U / N | unmount the image of the memory expansion, or name & save it to SD | | D / R | delete or rename a file on the SD card | | I | go to IECBuddy submenu () | | K | launch SIDKick (pico) configuration (only if detected) | | £ | timings configuration submenu |

(*) (only if IECBuddy detected)

IECBuddy submenu

The IECBuddy submenu is only accessible if an IECBuddy (image shows one of the variants) has been connected to the RAD before booting. You can synchronize files on the SD card with the internal flash storage of the IECBuddy, and newly created files on the IECBuddy are transfered to the subdirectory 'IECBuddy' in the RAD's 'PRG' folder.

| IECBuddy menu | command | |----------|:-------------| | T | transfer/sync files from and to IECBuddy (pending transfers are shown at the bottom) (**) | | 1..0, Q | select favorite disk-images for quick swap (button on the IECBuddy) remove from favorite list, note: imagescan also be mounted using DOS commands (as with SD2IEC) | | W | wipe all: remove all synced files from IECBuddy | | I | initialize the IECBuddy (= 'factory reset'), removes all files | | + / - | change drive number of the IECBuddy | | ← | back to main menu |

(**) if you transfer disk images (D64, D71, etc.) you can provide a .gif-image (240x160 resolution) which is displayed on the IECBuddy-TFT-screen once the image is mounted.

Printer emulation with the IECBuddy

The IECBuddy emulates a printer (device #4). When you print on the C64/C128 and go back to the RAD menu you can preview and save the print by pressing 'I' (go to IECBuddy submenu) in the main menu.

| print submenu | command | |----------|:-------------| | F7 | see a preview of the print | | RETURN | save the print (type in name before). The print will be save as PDF and series of BMPs on the SD-card in the sub-folder 'RAD_PRINT'. | | ← | back to main menu |

In the print preview you can scroll and zoom through the entire (multipage) document:

| print preview | command | |----------|:-------------| | cursor keys, or WASD | scroll over printout | | + / - | zoom | | SPACE | reset scaling | | F1 / F3 | go one page up / down | | F2 / F4 | go to first / last page | | HOME / DEL | go to begin / end of current page | | F7 or ← | close preview |

How to build a RAD Expansion Unit:

This sections summarize building and setting up the hardware.

PCBs, BOM and assembly information

There are two variants of the PCB: a larger one that fits the dimensions of the Raspberry Pi 3A+/3B+ and a smaller one which is tailored for the Raspberry Pi Zero 2. All is interchangeable, i.e. you can use either PCB with any of the supported RPis.

Here you can find the BOM and assembly information for RAD v0.1; both PCBs have exactly the same location of components, except for the buttons. Sourcing components: you can use LVC and LVX types for the 245, 257, and 573 ICs, you can use a 74LS30 or 74HCT30, make sure that you get the correct CBTD3861. The tactile switches, socket and ICs cost about 4 to 6 EUR/USD/CAD from reknown vendors such as Mouser, Digikey, TME if you buy components to 10 RADs (add about 20% if you only buy for one). Including the PCB the costs easily stay below 7 to 9 EUR/USD/CAD. (everything without shipping.)

PCB ordering

If you want to support my projects, feel free to order the PCBs from PCBWay:

RAD for RPi 3A+/3B+
RAD for RPi Zero 2
If you don't have an account at PCBWay yet: register via this link and get "$5 of New User Free Credit".

The Gerber files for PCB-production are also available in this repository if you want to order from another PCB manufacturer.

Build instructions

The first step when building the RAD is soldering the surface-mount components (bottom side only). Next solder the socket for the Raspberry Pi (2x20 female pin header), the pin header and push buttons. That's it!

3D printed cases

bigby has designed a case for 3D printing for both the RPi 3A+ RAD-PCB (see image above, courtesy of bigby) and the Zero2 PCB. The files can be downloaded on Thingiverse and Printables. As the PCBs have the some format as the Sidekick64 PCBs, other cases might be easy to adapt.

Quick start

Simply copy the release files onto an SD card (FAT32 formatted). You might want to have a look at the configuration file SD:RAD/rad.cfg, where you can setup the preferred startup mode (menu, as REU, or as GeoRAM). Also copy your REU/GeoRAM-images and .PRGs to the respective subdirectories.

From the menu you can select/browse using the keyboard. Press 'H' for help.

If you want to change the menu music, you can replace SD:RAD/music.wav. The format is a standard .WAV-file (preferred: mono, 15.6kHz, 8-bit PCM) of max. 8mb.

Powering the RAD Expansion Unit

Please use an external power supply for the RPi. Although the circuitry has pull-ups/pull-downs to not mess with the bus at boot time, the safest way is to boot the RAD first and then turn on the C64/C128.

Alternatively you can power the RAD from the C64/C128 using the "close to power..."-jumper. The current of the RPi has been measured and stays within the specifications of the expansion port, but (for some still unknown reason) it requires a quite strong and very stable power supply and often does not work at all. If it does and you experience any instabilities when powering from the expansion port (e.g. crashes during NUVIE-playing) it's most likely because of that. This is why I strongly recommend to use a good external power supply.

Important: NEVER power the RAD from the computer and externally at the same time. NEVER!

Overclocking

The Raspberry Pi configuration (SD:config.txt) overclocks the RPi (moderately for the RPi 3A+/B+, pretty significant for the Zero 2). Although I never experienced any problems with it, please be aware that overclocking may void warranty. In case you feel that RAD is not running stable, feel free to experiment with the values (some hints given in the configuration file), and let me know which settings work best for your configuration!

Configuration Details, Trouble Shooting

The bus timings and cache paramet

RAD

Install / Use

README