Alternative flashing methods

With Raspberry Pi (~3min)

  1. Install wiringPiopen in new window, if not already installed.

  2. Install flash_cc2531open in new window :

git clone
  1. Connect the following pins of the debug port to the GPIO port :
  • pin 1 (GND) --> pin 39 (GND)
  • pin 7 (reset) --> pin 35 (GPIO24, BCM19)
  • pin 3 (DC) --> pin 36 (GPIO27, BCM16)
  • pin 4 (DD) --> pin 38 (GPIO28, BCM20)

Optionally, connecting Target Voltage Sense to a 3.3v source (Red wire) eliminates the need to plug the device into a usb port, so optionally connect the following too:

  • pin 2 (Target Voltage Sense) --> pin 1 or pin 17 (3.3v) on Raspi

See above for the dispositions of pins on CC2531, and at in new window for pins on Raspberry.

A downloader cable CC2531 and 4 Dupont line Female to Female are perfect for this purpose. If you don't want to buy a downloader cable, you need to bend the debug pins outwards to be able to connect your Dupont cables since the pins are too close together to connect the Dupont cables directly.

Now insert the usb dongle in an USB port :

  1. Test by running :
cd flash_cc2531

it should return :

  ID = b524.

If you see 0000 or ffff, something is wrong and you should probably check your wiring.

  1. Download and extract the latest firmware CC2531_DEFAULT_20211115.zipopen in new window.
cd ~/flash_cc2531       #assuming you git-cloned the program to your home directory
  1. Erase and flash the CC2531 :
./cc_write CC2531ZNP-Prod.hex

It takes around 3 minutes.

Via Arduino Uno/ESP8266 with CCLoader (~3min)

This has been tested with a Genuine Arduino Uno, an Arduino Pro Micro - China clone, and a NodeMCU ESP8266 and is significantly faster than CCLib

Prepare the firmware

  1. Download the correct firmware (in this example we'll be using the CC2531 firmwareopen in new window)

  2. Unpack firmware and convert the hex file to binary using objcopy (do not use the included binary file!)

    Windows: download objcopy.exe as per thisopen in new window answer from StackOverflow.

    objcopy.exe --gap-fill 0xFF --pad-to 0x040000 -I ihex CC2531ZNP-Prod.hex -O binary CC2531ZNP-Prod.bin

    Linux or Bash on Ubuntu on Windows: install the binutils package using your package manager

    objcopy --gap-fill 0xFF --pad-to 0x040000 -I ihex CC2531ZNP-Prod.hex -O binary /tmp/CC2531ZNP-Prod.bin

Prepare CCLoader

  1. Download and unpack CCLoaderopen in new window
  2. On Windows you can use the precompiled CCloader.exe
  3. On Linux you have to compile CCLoader yourself so change directory to CCLoader/SourceCode/Linux, and run
    gcc main.c -o CCLoader

Flashing the Arduino or ESP8266 and the CC2531 device

  1. For Arduino, leave the pins set as default in 'Arduino\CCLoader\CCLoader.ino' (lines 86-90):
// Debug control pins & the indicate LED
int DD = 6;
int DC = 5;
int RESET = 4;
int LED = 13;

For ESP8266 (NodeMCU or WeMos D1 Mini) edit those pins in 'Arduino\CCLoader\CCLoader.ino' (lines 86-90) to usable pins for the ESP8266, these worked for me (note that the number is the GPIO number, not the label on the NodeMCU):

// Debug control pins & the indicate LED
int DD = 14; //GPIO14=D5 on NodeMCU/WeMos D1 Mini
int DC = 4; //GPIO4=D2 on NodeMCU/WeMos D1 Mini
int RESET = 5; //GPIO5=D1 on NodeMCU/WeMos D1 Mini
int LED = 2; //GPIO2=D4 and the Blue LED on the WeMos D1 Mini and the ESP-12E module on the NodeMCU, or can use GPIO16=D0 for the other Blue LED on NodeMCU
  1. Flash Arduino Uno or ESP8266 board with Arduino\CCLoader\CCLoader.ino (For NodeMCU on Windows: install the Arduino IDEopen in new window, then in Preferences, add the following URL to the Additional Boards Manager URL field: , then go to the Boards Manager and install the esp8266 package, then set the board to "NodeMCU 1.0 (ESP-12E module)" or if you are using a WeMos D1 Mini set it to "LOLIN(WEMOS) D1 R2 & Mini", then set Port to the correct COM port (it was COM3 for me with a NodeMCU), then Upload the sketch.)

  2. Note the COM port number or device name as this will be used later

  3. Connect Arduino pins as described below to the debug header of the CC device

    ArduinoCC PinCC Name
    D53DC (Debug Clock)
    D64DD (Debug Data)

    If you have a 3.3V Arduino you can optionaly connect 3.3V -> Target Voltage Sense (Pin 2) and program the CC2531 without connecting the CC2531 to USB (in the next step).

    Connect the ESP8266 pins as described below to the debug header of the CC device

    ESP8266CC PinCC Name
    D2/GPIO43DC (Debug Clock)
    D5/GPIO144DD (Debug Data)

    C2531 debug pinsCC2531 stick and NodeMCU

  4. Connect Arduino/ESP8266 first, then within a couple seconds connect the CC2531 to USB power

  5. Place the prepared CC2531ZNP-Prod.bin next to the executable file

  6. Start the flashing process


    CCLoader_x86_64.exe [Number of the COM port] CC2531ZNP-Prod.bin 0

    Example: Arduino UNO on COM7

    CCLoader_x86_64.exe 7 CC2531ZNP-Prod.bin 0


    ./CCLoader [Name of the USB device] CC2531ZNP-Prod.bin 0

    Example: Arduino Uno on /dev/ttyACM0

    ./CCLoader /dev/ttyACM0 CC2531ZNP-Prod.bin 0

It should be done in a few minutes.

If burning fails/gets stuck at Request sent already! Waiting for respond... - try again, check your wiring, try using 1 instead of 0 as the last parameter. Or try run command with sudo.

Via Arduino/ESP8266 with CCLib (~3hrs)

Flashing firmware via Arduino is implemented using the project But with minor improvements!!!

AndrewLindenopen in new window described that he was able to flash CC2531 using CCLib with commentsopen in new window.

As described I made a fork of the CCLib library with minor changesopen in new window for flashing firmware via Arduino:

  • Timeouts of operations
  • After opening the port (I have in Windows 7) Arduino reboots and, accordingly, does not respond to requests - made a 3 seconds pause (found somewhere in internet).
  • The port speed is reduced to 9600, because at another speed leaving communication errors: ERROR: Could not read from the serial port!

Flashing process:

  1. Download and unpack the archive with the library

  2. Flashing Arduino sketch via Arduino IDE CCLib\Arduino\CCLib\Examples\CCLib_proxy\CCLib_proxy.ino

If flashing via esp8266 (wemos d1 mini), you need change connection (p. 5) and Pinout configuration in Arduino/CCLib/Examples/CCLib_proxy/CCLib_proxy.ino:

int CC_RST   = 5;
int CC_DC    = 4;
int CC_DD_I  = 14;
int CC_DD_O  = 12;
  1. Install Python 2.7 or later (tested with python 2.7.13), if not installed

  2. Install pyserial 3.0.1, if not installed pip install -r CCLib\Python\requirements.txt or pip install pyserial==3.0.1

  3. Connect the contacts as described But in my case, I connected completely without resistors, combined the contacts CC_DD_I and CC_DD_O together and connected to the DD pin of the DEBUG connector!

I connected only 3 specified contacts and GND. During the firmware, the stick and Arduino must be connected to the USB.

  1. After that, try to get information about the chip - if it works, then the connection is correct (example for COM9 port - Arduino port):
C:\Projects\CCLib\Python>python -p COM9
INFO: Found a CC2531 chip on COM9

Chip information:
      Chip ID : 0xb524
   Flash size : 256 Kb
    Page size : 2 Kb
    SRAM size : 8 Kb
          USB : Yes

Device information:
 IEEE Address : 00124b0014aa
           PC : 0000

Debug status:

Debug config:

Another example of connection on MacOSopen in new window

  1. If everything is successful, download the firmwareopen in new window. Before we flash the firmware we need to make a modification to it. Open the .hex file in a text editor and remove the second last line. Now save the file.

  2. Start the flashing firmware (it takes a long time, about 2-3 hours):

C:\Projects\ZigBee>python -e -p COM9 --in=CC2531ZNP-Pro-Secure_LinkKeyJoin_mod.hex
INFO: Found a CC2531 chip on COM9

Chip information:
      Chip ID : 0xb524
   Flash size : 256 Kb
    Page size : 2 Kb
    SRAM size : 8 Kb
          USB : Yes
Sections in CC2531ZNP-Pro-Secure_LinkKeyJoin_mod.hex:

 Addr.    Size
-------- -------------
 0x0000   8176 B
 0x1ff6   10 B
 0x3fff0   1 B
 0x2000   239616 B

This is going to ERASE and REPROGRAM the chip. Are you sure? <y/N>:  y

 - Chip erase...
 - Flashing 4 memory blocks...
 -> 0x0000 : 8176 bytes
    Progress 100%... OK
 -> 0x1ff6 : 10 bytes
    Progress 100%... OK
 -> 0x3fff0 : 1 bytes
    Progress 100%... OK
 -> 0x2000 : 239616 bytes
    Progress 100%... OK