Jump to content

SD2IEC & IEC-2-SD Adapters

From RetroTechCollection
SD2IEC & IEC-2-SD Adapters
Caption TFW8b SD2IEC v5B – turnkey unit with OLED, buttons and IEC-passthrough
Type SD-card IEC serial mass-storage adapter (1541-compatible subset)
Designer Community project
originated as MMC2IEC by Lars Pontoppidan (2007); maintained by Ingo Korb (sd2iec firmware)
Manufacturer Unknown
First released 2008 (sd2iec v0.1)
Latest revision sd2iec firmware v1.1.1 (March 2024)
Operating voltage +5 V from IEC bus • on-board 3.3 V LDO for SD-card
Layers / PCB —
Compatibility C64 / C64C / SX-64 / C128 / VIC-20 (CR) / Plus-4 / PET (via IEEE–IEC adapter)
Features —
Model No. uIEC/SD, SD2IEC (v4–v5B), SD2IEC Slim/OLED, IEC-2-SD ARM, SaRuMan-SD, numerous DIY

The SD2IEC family—and its ARM-based off-shoots usually sold as IEC-2-SD—are open-hardware adapters that let Commodore 8-bit machines read and write FAT/FAT32-formatted SD-cards through the standard IEC serial bus. Acting as a *smart* disk-drive clone they implement the most-used 1541/1571/1581 DOS commands (LOAD, SAVE, directory, block API, ↑, ←, etc.) plus a small command channel interpreter that maps files and sub-directories to disk images on the card.

Quick facts
[edit | edit source]
  • “Loader-ready in < 1 s” – no mechanical spin-up / head-seek delays.
  • Capacity: 32 GB+ per card, thousands of ‘‘D64/D71/D81’’ images or plain PRGs.
  • Speed: ≈ 45× stock 1541 with JiffyDOS fast-loader (≈ 12 kB s-1).
  • Firmware upgradable from the C64 itself (`LOAD "FW.BIN",8,1` & `RUN`).
  • 100 % open-source: hardware KiCad / Eagle files & AVR/ARM firmware on GitHub.

📜 History

[edit | edit source]
  • 2006-07 – MMC2IEC — Lars Pontoppidan prototypes an ATmega32 board that translates IEC ↔ SPI-MMC.[1]
  • 2008 – sd2iec — Ingo Korb forks the code, adds FAT32, long filenames, D71/D81 and renames the firmware sd2iec.[2]
  • 2010-12 – Commercial kits — Jim Brain's uIEC/SD and NKC Electronics sell through-hole DIY modules.
  • 2014-15 – TFW8b v4/v5 — TheFutureWas8bit releases compact SMD units with button board & OLED.
  • 2018 – IEC-2-SD (STM32) — Petter Lundsten ports the protocol to the STM32 “Blue Pill”, bringing USB mass-storage gadget mode.[3]

🛠️ Hardware architecture

[edit | edit source]
Variant MCU Clock RAM Notes
Classic SD2IEC ATmega1284P 20 MHz crystal 16 KB SPI→SD, UART→debug, optional OLED/I²C
uIEC/SD ATmega644P 16 MHz 4 KB 2× micro-SD sockets, daughter-card form factor
IEC-2-SD STM32F103C8T6 72 MHz 20 KB SRAM USB-C, full-speed USB gadget (card seen as drive on PC)
SaRuMan-SD ATmega1284P 24 MHz (X-tal) 16 KB Sidekick64 plug-on module, exposed JTAG

Most boards power entirely from the +5 V IEC bus (≈ 100 mA). A 3 V LDO or DC/DC step-down supplies the SD slot. Level-shifting is done by resistor networks or BSS138 FETs depending on revision.

⚙️ Firmware features

[edit | edit source]
  • DOS Commands: `LOAD, SAVE, OPEN, B-A (block execute), VALIDATE`, etc.
  • Disk image hot-swap using buttons (NEXT / PREV) or via `OPEN 15,"CD:somedir"`.
  • Long-file-name to C64 PETSCII mapping (configurable).
  • GEOS support (`U0>M0`) and native fast-loader patches for JiffyDOS, Final Cartridge III, Epyx FastLoad, SJLoad, etc.
  • Config file `sd2iec.cfg` – set default device #, Jiffy mode, drive # mapping, LED polarity.
  • IEC passthrough so real 1541s can daisy-chain behind the adapter.

Known limitations

[edit | edit source]
  • No true 6502-cycle-exact 1541 CPU emulation ⇒ copy-protected titles that rely on drive-side code or nibble-level flux patterns fail.
  • Relative files not supported.
  • Burst-mode fast-loaders designed for the 1571/1581 may require a parallel-IEC mod or fail altogether.
  • Command channel buffers are 254 bytes – very long `@` commands can overflow.

🚀 Fast-loader compatibility matrix

[edit | edit source]
Loader Stock C64 JiffyDOS SD2IEC (AVR) IEC-2-SD (STM32)
JiffyDOS (KERNAL) ✗ ✔ ✔ 45× ✔ 45×
Epyx FastLoad (cart) ✔ 5× ✔ 5× ✔ 30× ✔ 35×
Final Cartridge III ✔ 6× ✗ ✔ 32× ✔ 34×
Dolphin DOS ✗ ✗ — —
Fast Load V5 PAL ✔ ✔ ⚠ (needs ``OPEN15,"UX"` patch) ✔

🔌 Using SD2IEC

[edit | edit source]

<plainlist>

  • Device number – shipped as *8*; change with `OPEN15,8,15,"U0>"+CHR$(10+new#):CLOSE15`.
  • Browse directories – `LOAD"$",8` or use FB64 file-browser PRG on the card root.
  • Mount D64 image – `OPEN1,8,15,"CD:DEMOS/DISK1.D64":CLOSE1`.
  • Swap image – front buttons (NEXT/PREV) or `OPEN15,"XS:next":CLOSE15`.
  • Firmware update – copy `firmware.bin` to card root → reset while holding “NEXT”.

</plainlist>

🆚 Pi1541 / 1541 Ultimate

[edit | edit source]
Feature SD2IEC / IEC-2-SD Pi1541 1541 Ultimate-II+
MCU / SoC 8-bit AVR / STM32 Raspberry Pi (ARM) FPGA (Cyclone III)
Cycle-exact 6502 emulation ✗ ✔ ✔
Copy-protected G64 / TAP ✗ ✔ ✔
Price (2024) US$25-60 US$60-90 US$200+
Plug-and-play (no Pi setup) ✔ ⚠ SD card image & config needed ✔
Real-time clock, Ethernet, RAM-expansion ✗ ✗ ✔
[edit | edit source]
Brand / Model Notes Approx. price (2024)
TheFutureWas8bit SD2IEC v5B OLED, 3 buttons, IEC thru, 3-D printed shell £34 GB
Retro-Port uIEC/SD Daughter-card w. 6-pin header, fits internal C64 installs US$44
Pi1541 Zero (not SD2IEC) Cycle-exact but needs Pi Zero – see separate page €49
IEC-2-SD “BluePill edition” STM32, USB-C, optional OLED, DIY kit €29 kit / €45 built

🔧 DIY resources

[edit | edit source]

📚 See also

[edit | edit source]

📝 References

[edit | edit source]
  1. ↑ Pontoppidan, L. “MMC2IEC project log”, Usenet comp.sys.cbm, 2007-02-19.
  2. ↑ sd2iec official wiki, “Development timeline”.
  3. ↑ Lundsten, P. “IEC-2-SD readme”, GitHub, 2019-05-03.
[edit | edit source]
Retrieved from "https://wiki.retrotechcollection.com/index.php?title=SD2IEC_%26_IEC-2-SD_Adapters&oldid=2826"