Floppy Disk IF
Interface 5.25" single-sided Shugart floppy drives (and Gotek emulators) to any 6502 computer. Based on the Elektor Junior FDC.
Floppy Disk IF
What is it?
A Printed Circuit Board for a floppy disk controller. It interfaces 5.25-inch single-sided Shugart-type floppy disk drives to generic 6502 computers. Also fully compatible with Gotek floppy emulators running FlashFloppy firmware and .HFE disk images.
Why did I make it?
I have a love of 6502-based systems from around 1979 when I built my first kit computer (UK101) and expanded it with a floppy disk drive. I still had my original 5.25" disks and wanted to recover the software I had written 40 years ago. This interface is not available elsewhere, so I had to research and design the PCB myself.
After completing the build I connected my old Teac 504 drive and attempted to boot from a 40-year-old master diskette. After a few tick-ticks from the drive, OS65D3.0 booted perfectly!
What makes it special?
Based on the Elektor Junior FDC, designed for OSI-65D and Shugart 5.25" floppy disks. The PIA and ACIA are memory-mapped as per the OSI standard:
| Device | Address |
|---|---|
| PIA (6821 or 6521) | $C000 |
| ACIA (6850) | $C010 |
Bill of Materials
| Component | Quantity | Value / Part |
|---|---|---|
| ACIA | 1 | 6850 |
| PIA | 1 | 6821 or 6521 |
| Bus Transceiver | 1 | 74LS245 |
| Decoder | 2 | 74LS138 |
| Monostable | 1 | 74LS123 |
| Flip-flops | 1 | 74LS74 |
| Logic gates | Various | 74LS series |
| Capacitors | 13 | 0.1µF |
| Capacitors | 2 | 1nF |
| Capacitors | 2 | 47µF |
| Resistors | 5 | 150Ω |
| Resistors | 1 | 1KΩ |
| Resistors | 3 | 4.7KΩ |
| Resistors | 1 | 6.8KΩ |
| Variable resistors | 2 | 10KΩ |
| Diode | 1 | 1N4148 |
| Headers | 4 | 16-pin |
| Headers | 2 | 17-pin |
| Headers | 1 | 36-pin right-angle |
36-Pin Bus Connector
D7 D6 D5 D4 D3 D2 D1 D0 A15 A14 A13 A12 A11 A10 A9 A8 A7 A6 A5 A4 A3 A2 A1 A0 NC PHI2 R/W NC NC NC NC NC GND NC NC +5V
Hardware Versions
Version 2.3A note: If you have an early v2.3A board, a strap is required between D1 cathode and pin 16 of the 74LS123. Later boards have this resolved.
OSI Superboard / UK101 users: If connecting to an original Superboard or UK101 that already has expansion boards, you may need to bypass the 8T88-buffered connections.
Downloads
Original OS Disk Images (5.25" Shugart format):
Gotek / HFE Format Images:
Schematics & Images
