After winning a cheap bid on a Commodore 64 off eBay the other day I’ve looked into building a SD2IEC.
The SD2IEC is a storage device using an SD card and interfacing with the IEC bus using a ATMega644 microcontroller.
I already had a SD Card with a built in 3.3 voltage regulator so did’t need to add this into the build. Also used the ATMega1284
First step is to program the microcontroller with a bootloader. Having already built a USB Tiny ISP it was a simple step to program it. Schematic for this I got from AdaFruit
Bootloader files are available from sd2iec.de
Download /bootloader/newboot-0.4.1-binaries.zip, extract the files and write
newboot-0.4.1-larsp-m644p.hex to the microcontroller. I used avrdude:
avrdude -c usbtiny -p m1284 -e -V -U flash:w:newboot-0.4.1-larsp-m1284p.hex
avrdude -c usbtiny -p m1284 -U lfuse:w:0xd7:m -U hfuse:w:0xd2:m -U efuse:w:0xfc:m
Next comes building the circuit. I used a veroboard and there were not that many components to add. Didn’t have to use R1-R6 as they were already on the SD Card.
Data cable pinouts
Not as pretty as the bought ones but it didn’t cost me anything to build and was a fun project.
After assembling copy the S2IEC firmware to the root of the SD Card. Power on and the red LED will flash for two seconds while it looks for a valid firmware. The green LED should then flash while it accesses the card. When it starts to flash the firmware the green LED will flash rapidly.
To test if the computer is successfully connecting to the SD2IEC device you can use the following simple program:
30 PRINT A$,B$,C$,D$
This will print the current SD2IEC firmware to the screen.