Skip to content


Switch branches/tags

Latest commit


Git stats


Failed to load latest commit information.
Latest commit message
Commit time


This is a combination of an Arduino sketch, a Python script and a C# GUI application to read and write the firmware of the Realtek RTD266x flat panel display controller. The Arduino code is based on ladyada's project.

There are special features included for a 3.5" HDMI display manufactured by KeDei, which is equipped with an RTD2660: you can replace the boot logo with a custom logo, change the background and foreground colors and modify the "HDMI" pop-up. The custom logo needs to be 204x72 pixels and may only contain black and white pixels.

Custom logo


In order to modify the RTD266x's firmware, you need to establish a connection to the chip. There are two ways to do that:

  1. You can connect the display via HDMI to a Raspberry Pi, enable the I²C HDMI driver and read/write the firmware using the Python script without any additional hardware. The firmware will be stored in a file which you can open and modify with the C# GUI tool. The modified file is then written back to the display with the Python script.

  2. You connect an Arduino to the display's I²C pins using a modified HDMI cable. The Arduino is connected to a PC/laptop and controlled with the C# GUI tool.

If you don't have Microsoft Visual Studio to compile the C# GUI tool, you can download the EXE file from the releases.

Method 1: Arduino

Compile the RTD266xArduino sketch with the Arduino IDE and download it onto your Arduino. You can close the Arduino IDE afterwards.


The communication between display and Arduino is done via I²C which is accessible on the VGA and HDMI ports of RTD266x. Connect SCL, SDA and GND with the corresponding Arduino pins.

For an Arduino Uno and an HDMI connector type A, this would be:

Pin name Arduino Uno HDMI type A
SCL A5 15
SDA A4 16

There are no additional pull-ups required, they are already on the RTD266x PCB.

Connect the display and Arduino as mentioned above. Power on the display first, then the Arduino.

A flashing user LED on the Arduino indicates a problem with the connection. Reset the Arduino to try again and use the GUI tool to read the error info.

Setup example

GUI tool

Start RTD266xFlash.exe and select Connect directly with an Arduino. Select the COM port your Arduino is connected to and click Connect. If there was an error it will tell you what went wrong. You can click Read status to check the connection and read some info about the flash chip. It should return values different from 0x00 and 0xFF. If it doesn't, try again or reset the Arduino.

If you get an error about an unknown JEDEC id, uncomment or add the correct JEDEC id in rtd266x.cpp. Compile and download the sketch again to your Arduino and try again.

Screenshot of GUI tool

Ruby tool

Instead of the GUI tool written in C#, you can use a Ruby tool on the command line written by kivikakk.

To read the flash into the file flash-contents.bin, call it like this:

ruby flash.rb SERIAL dump

Replace SERIAL with your serial port (for example COM1 on Windows, /dev/ttyACM0 on Linux or /dev/cu.usbmodem3201 on a Mac).

To write back the firmware, use this command:

ruby flash.rb SERIAL write FILE [OFFSET LENGTH]

Call the tool without parameters to get a detailled description of its parameters.

Method 2: Firmware images with Python script

For this method you need a Raspberry Pi running a current version of Raspbian or any derivative. Use a standard HDMI cable to connect the display to the Raspberry Pi. In your /boot/config.txt file you need to add the following line to enable the I²C on HDMI interface:


For the Raspberry Pi 4 and modern firmware you need to change the line




You will also need to install the I²C Python library with this command:

sudo apt-get install python-smbus

After a reboot, enable the I²C driver by executing:

sudo raspi-config

Navigate to Interfacing Options, I2C and select Yes. Use Back and Finish to leave the configuration tool.

Get a list of available I²C busses:

i2cdetect -l

You can then scan for I²C devices with this command on a specific bus:

sudo i2cdetect -y I2CBUS

where I2CBUS is the bus number you got from the previous command, i.e. sudo i2cdetect -y 2.

It should find a device at address 4a.

To download the Python scripts, run the following commands:

  1. cd ~
  2. git clone
  3. cd RTD266xFlash/RTD266xPy

You are now ready to read the display's firmware with this command:

python -i I2CBUS -r 524288 out.bin

Replace I2CBUS with your bus number. The number after parameter -r is the firmware's size in bytes (512 x 1024 = 512 KB). This will take about 2 minutes. Transfer the file out.bin to your PC/laptop where you have the GUI tool RTD266xFlash.exe. Start it and select Firmware images. Select out.bin as the input file and configure the modifications you want to perform. Click Modify firmware and save the modified firmware file.

Screenshot of GUI tool

Screenshot of GUI tool

Transfer the modified firmware file to the Raspberry Pi and run

python -i I2CBUS -d out.bin out_modified.bin

where I2CBUS is the bus number and out_modified.bin is the modified firmware file. This will write all modified sectors of file out_modified.bin to the display, skipping the unmodified sectors to speed things up. Enjoy your modified firmware!

Expert knowledge: details of firmware modifications

Attention: Before you modify your firmware, create a backup of the original firmware!

An Intel 8051 MCU is integrated in the RTD266x which runs the firmware. If you compile the source code (Source 1 and source 2) and set the compiler to output the assembler listings, you can easily find matching code areas within the binary firmware. By manipulating the instructions, we can modify the firmware's behaviour.

Here are some examples for the KeDei 3.5" display. There are different firmware versions for different PCB revisions and panel types. All firmwares are 512 KB. They are assigned numbers to refer to them:

# Hardware MD5 Hash SHA1 Hash
1 PCB V 1.0 C501EB83693372E1089B096B024F2E9F 08B253C9B757BC700AFC057F3836878BE866C05C
2 PCB V 1.1, panel type 1 (SKY035S13B00-14439) 83B41D1682E7CB7DED3A0241518A3D96 1C675660BF478E687CD09912EF77D2A86E93525E
3 PCB V 1.1, panel type 2 (SKY035S13D-199) v1 0FA74E1AF51B56A84AA4D4DD4D97383E 09E16041E390F9804EA6F734DCB1AACC4A0DC97B
4 PCB V 1.1, panel type 2 (SKY035S13D-199) v2 22AF4BE65892FA772D8699DD030837DC 3E80A0B3C1DA0E726A1FCF6D31DED497C0B65429
5 PCB V 1.1, panel type 3 (SKY035S13E-180) v1 906A447A4E0D182669228EC75E581E78 9DAC069E130FC7638D90E031C2E36819344703AD
6 PCB V 1.1, panel type 3 (SKY035S13E-180) v2 B55F67DA7A609C954EBB75FCDF877F7D DEC9911C8C1D150D069BAB1D1E42792665E62AD8

Change background color to black

The background color is set by calling function CAdjustBackgroundColor. For firmware #1 this function is located at 0xD237 - 0xD27A, for firmware #2 at 0xD432 - 0xD475, for firmware #3 at 0xD2A5 - 0xD2E8 and at 0xD2C9 - 0xD30C for firmware #5. At function offsets 0x2C (#1: 0xD263, #2: 0xD45E, #3: 0xD2D1, #5: 0xD2F5) and 0x3C (#1: 0xD273, #2: 0xD46E, #3: 0xD2E1, #5: 0xD305) the instruction is 0xE0 (MOVX A,@DPTR). By changing this to 0xE4 (CLR A) the background color is always set to 0x000000, which corresponds to black.

Change logo colors

The boot logo uses two colors, which are picked from a color palette consisting of 16 3-byte (red, green, blue) entries. The palette is located at 0x13A31 (firmware #1, #2, #3 and #5). The foreground color is 0xFFFFFF (white) at 0x13A3A. The background color is 0x0000FF (blue) at 0x13A5B. By changing 0x13A5D to 0x00 we can change the background to black.

Change "HDMI" pop-up text

After the display is powered on and has shown it's logo, a small pop-up shows the input source. The text "HDMI" can be changed easily. You won't find the ASCII characters in the firmware, but you can refer to tGlobalCharWidth in OSD/OSD003/OsdRes003.c to decode and encode a string. Some wide characters like A, G, M, W etc. are composed of two font entries. You can find the "HDMI" string by searching for 19 14 1E 1F 1A 00 (offset 0x12346 for firmware #1, #2, #3 and #5). It can be replaced by a custom string but shouldn't be much longer.

Disable "HDMI" pop-up

The "HDMI" pop-up is shown by the function CShowNote. It is located at 0x14733 (firmware #1, #2, #3 and #5). By changing it's first instruction at 0x14733 to 0x22 (RET), we force an immediate return from this function and no pop-up is shown.