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tinyDiskII

Homemade floppy disk emulator for Apple II series computers

⚠️ Work in progress: read carefully the README before trying to reproduce this project!

tinyDiskII

tinyDiskII is able to simulate an Apple Disk II both in reading and writing. Disk images are stored into a FAT16 formatted SD Card. Each disk image must be a DOS 3.3 floppy image, saved as .NIC. A cross platform .NIC <-> .DSK conversion tool will be available soon on this repository. Floppy formatting is currently not supported, but it is currently under developement.

BOM

Reference(s) Description Notes
C1, C2, C3, C4, C5, C6, C8, C9, C10, C11, C12 0805 100n Capacitor
D1, D2 0805 Red LED
J1 2x3 male jumper ICSP connector
J2 SMD SD Card slot
J3 THT USB B Mini connector Mount for USB debug
J4 2x10 male connector DiskII connector
R5, R6 330
R2, R3, R4, R7, R8, R9, R10, R11, R12, R15 10k
R13, R14 0 Replaced with a bridge
SW1 RotaryEncoder with switch
U2 SN74LVC244 5V tolerant buffer
U3 CH340C Mount for USB debug
U4 ATxmega16A4U-A MCU
U5 74AHCT125 Level shifter
U7 0.96" OLED I2C 7-pin model
U10 AP1117-33 3v3 linear regulator

Do Not Place, reserved for future implementations:

Reference(s) Feature
U1 Flash/EEPROM interface
C12 "
R1 "
C13, C14 USB ESD
R13, R14 "
D3, D4 "
C7 USB self reset
J5 Debugging connector

Schematics and PCB

⚠️ Schematics and PCB layout can be found in /schematics folder. Please note that I had physically implemented only rev1.0, which requires some hardware patches. The issues were fixed in rev1.1, but I never put it into production. Build it at your own risk.

Firmware

Firmware source code is in /firmware folder. Code can be compiled on a linux/wsl machine through make command. Make sure you have make and avr-gcc toolchanin installed. Output binary will be generated as /firmware/output/tinyDiskII.hex.

In /firmware/tests there are some unit tests that can run on host system. They can be compiled and executed with:

cd firmware/tests
cmake -B build .
cd build
cmake --build .
./tinyDiskII-tests

Changelog

  • rev1.0: first version

  • rev1.1: fixes the issues present in rev1.0:

    • LV_DISK_READ connected to U4 pin 21;
    • SD_WP connected to U4 pin 22;
    • SD_DETECT connected to U4 pin 23;
    • Added 10K pull-up resistor to DISK_WRITE_EN;
    • Pin 4 and 16 of U3 are shorted together.

Contributors and references

The whole projects borns as a custom implementation of Koichi Nishida's SdiskII [1] [2], which I used as a starting point for firmware developement.