Editing SD2IEC & IEC-2-SD Adapters

{{Infobox hardware
| name           = SD2IEC & IEC-2-SD Adapters
| image          = [[File:SD2IEC-TFW8b-v5B.jpg|250px]]
| caption        = TFW8b SD2IEC v5B – turnkey unit with OLED, buttons and IEC-passthrough
| developer      = Community project<br />originated as '''MMC2IEC''' by Lars Pontoppidan (2007); maintained by Ingo Korb (''sd2iec'' firmware)
| type           = SD-card IEC serial mass-storage adapter (1541-compatible subset)
| first_released = 2008 (''sd2iec'' v0.1)
| latest_release = ''sd2iec'' firmware '''v1.1.1''' <small>(March 2024)</small>
| operating_voltage = +5&nbsp;V from IEC bus • on-board 3.3 V LDO for SD-card
| application    = C64 / C64C / SX-64 / C128 / VIC-20 (CR) / Plus-4 / PET (via IEEE–IEC adapter)
| model          = 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 =====
* '''“Loader-ready in &lt; 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<sup>-1</sup>).  
* '''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 ==
* '''2006-07 – MMC2IEC''' — Lars Pontoppidan prototypes an ATmega32 board that translates IEC ↔ SPI-MMC.<ref name="pontoppidan">Pontoppidan, L. “MMC2IEC project log”, Usenet comp.sys.cbm, 2007-02-19.</ref>
* '''2008 – sd2iec''' — Ingo Korb forks the code, adds FAT32, long filenames, D71/D81 and renames the firmware '''sd2iec'''.<ref name="sd2iec_wiki">''sd2iec'' official wiki, “Development timeline”.</ref>
* '''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.<ref name="iec2sd">Lundsten, P. “IEC-2-SD readme”, GitHub, 2019-05-03.</ref>

== 🛠️ Hardware architecture ==
{| class="wikitable sortable" style="text-align:center"
! 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 ==
* '''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 ===
* '''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 ==
{| class="wikitable"
! 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 ==
<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 ==
{| class="wikitable"
! 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 || ✗ || ✗ || ✔
|}

== 🛒 Popular ready-made units ==
{| class="wikitable sortable"
! 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 ==
* '''PCB & schematic:''' <https://github.com/IngmarK/sd2iec-hardware>  
* '''Firmware source:''' <https://github.com/sd2iec/sd2iec>  
* '''IEC-2-SD repo:''' <https://github.com/plundstr/IEC-2-SD>  
* '''Forum support:''' Lemon64 “sd2iec user thread”, retro-computing Stack Exchange tag ‘‘sd2iec’’.

== 📚 See also ==
* [[Pi1541 Full-Drive Emulator]]
* [[1541 Ultimate-II+ Cartridge]]
* [[Commodore IEC Serial Bus]]

== 📝 References ==
<references />

== 🌐 External links ==
* [https://sd2iec.de Official ''sd2iec'' wiki] – documentation, binaries, parts list.
* [https://www.thefuturewas8bit.com/ The Future Was 8-bit] – commercial SD2IEC hardware.
* [https://blog.retroleum.co.uk/ Retroleum blog] – tutorial “Compiling sd2iec on macOS”.