The GR-CITRUS tiny board enables easier programming with the Ruby language. You can create Ruby programs with Visual Studio Code. See VSCode Extension "Rubic". You can also develop with Rubic on the chrome app.


You can program similar to Arduino Sketch using the Renesas web compiler and IDE for GR.

By connecting with the WA-MIKAN board that has an ESP8266 module for Wi-Fi, you can prototype a system using Wi-Fi and a Micro SD card.



  • Renesas' 32-bit RX63N Group MCU is on board
  • Compatible pin array with Arduino Pro Mini
  • -FULL product attached long pin socket for WA-MIKAN (The image describes normal type)


  • Wi-Fi module "ESP8266" and Micro SD socket
  • -FULL has a pin socket for GR-CITRUS connection (The image describes full type)

GR-CITRUS Board Pin Map


Detailed Specifications

RX631(R5F5631FDDFP 100-pin QFP)
Data Flash
Main Clock
96MHz (internal)
Sub Clock
Operating Voltage
Board Function
Reset Switch, 20 expanding pin, User LED 1


Ruby Firmware

Download GR-CITRUS' latest firmware for Ruby. To write the firmware, please press the reset button of GR-CITRUS and recognize it as USB memory, then copy the bin file. Refer to GitHub for more about the latest firmware.

GR-CITRUS Ruby Firmware v2.35 (ZIP)

Project File for e2 studio

Project file for sketching in the Eclipse-based development environment e2 studio. For downloading and installing e2 studio, please refer to the e2 studio product page.

  • Click to download. Import the archive file (zip) as an existing workspace from the menu 'File' -> 'Import' in e2 studio.
    Citrus Sketch v223 Project File (ZIP)

Note: This is a project exported in e2 studio version 7.6.

USB Mass Storage Firmware

Download GR-CITRUS' USB mass storage firmware. To write the firmware, it's necessary to use Renesas Flash Programmer and close the MD jumper on the GR-CITRUS board to change to a programming mode with a USB direct connection.

At Version b, the volume label becomes "GR-CITRUS_b". Version b expands the bin write area from 528KB to 960KB. Depending on the OS of the PC, hidden files may be written to the storage, and the actual writing area may be reduced.

GR-CITRUS USB Mass Storage Firmware (ZIP)
(Version b, November 7, 2017)

Technical Support

Technical Information

Related Websites

GR-CITRUS Board Distributor



Gadget Renesas provides boards that make it possible to prototype ideas quickly, a community where users can interact, and events to help users build their projects to make their ideas a reality. Below are some projects that utilized the GR-CITRUS board.