Compute Module 4 POE Board

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Compute Module PoE Board
Compute Module PoE Board
Compute Module Acce D

Compute Module IO Board with PoE Feature, Composite Breakout Board for Developing with Raspberry Pi CM4 / CM4L





This is an IO board for evaluating the Raspberry Pi CM4 or being integrated into end products. the board feature PoE function, it can be used for all variants of CM4.Support POE power supply and 7~36V DC DC power supply, onboard 4 x USB3.2 Gen1.


1: Do not plug and unplug any device except USB and HDMI while the baseboard is working.
2: This model only supports a 5V fan and cannot work with the 12V fan. Please confirm the fan voltage before connecting.
3: Micro USB is used as the USB SLAVE interface to burn the image, and cannot be used as the OTG interface.
4: In normal use, it is necessary to provide at least 5V 1.5A power supply for CM4. Otherwise, there may be problems such as automatic shutdown, frequency reduction, and so on.
5: Onboard default 4 x USB 3.2 Gen1 interface.
6: When using the POE function, pay attention to check whether the switch supports PoE of the 802.3af network standard.
7: When you need to use POE, connect the POE jumper cap to the EN.
8: Two DISP interfaces cannot be used together by default.


Compute_Module 4 POE Board
Compute_Module 4
Compute Module 4 IO Board 5.png

What's on board


No. Component Description
1 CM4 connector Suitable for all variants of Compute Module 4
2 DC power port 7~36V DC wide range power supply, recommend 24W power adpater at least.
3 Gigabit Ethernet RJ45 with PoE support 10/100M auto-negotiation, for connecting router or switch with PoE function
4 USB SLAVE Interface Writing emmc for Compute Module 4
5 USB3.2 Interface 4 x USB 3.2 Gen1 interface for USB devices.
6 HDMI Interface Dual HDMI ports for dual 4K 30fps output.
7 RTC RTC battery holder. The real-time clock can be used to wake up, shutdown or reboot Compute Module 4.
8 CAM 2x MIPI CSI camera connectors.
9 DISP 2x MIPI DSI display connectors.
10 FAN Fan header, support PWM Fan.
11 FAN Power Select 5V or 12V voltage to drive the fan
12 IO-VREF/PoE selection IO-VREF:CM4 IO logic level: 3.3V or 1.8V
PoE: enable (EN) or disable (DIS)
13 40PIN GPIO header For connecting Raspberry Pi HATs
14 CAM0 and DISP0 I2C bus fit the jumpers when using CAM0 or DISP0
15 Misc configurations
16 Dual LED indicators red: Raspberry Pi power indicator
green: Raspberry Pi operating statusindicator
17 TF card slot (bottom side) insert a Micro SD card with pre-burnt system, to start up Compute Module 4 Lite

Special function pin description


No. PIN Description
1 PI BOOT The pin is low when booting. This pin is connected to USB SLAVE interface.
2 EEPROM WP Set it to LOW to avoid writing EEPROM
3 IP1/0 MXL7704 AN1/0 Pin of CM4 board
4 VADC COMP Video output
5 ETH IN ETH synchronize signal
6 PI_EN Synchronize with PI_RUN signal
7 PI_GLOBAL_EN MXL7704 power enable pin of CM4, Low to disable.
8 PI_RUN CM4 status pin, high for On. Pull-down it to foruce reset the CM4
9 WIFI_EN WIFI enable pin, Low to disbale, and NC to enable.
11 BT_EN Bluetooth enable pin, Low to disable and NC to enable.


Do not plug or unplug any device while the base board is powered on.

Writing Image


  • Note: Please connect the fan before turning on the power of the base board and then complete the test. Please do not connect the fan after the base board is powered on, because the fan control chip has been powered on, otherwise the chip will be burned!
  • Note: Before connecting, please confirm whether the rated voltage of the fan is consistent with the voltage actually connected to the fan.

Please note that DSI and CSI are prohibited when using RTC.
I2C-10 is used by default

RTC (PCF85063a) on i2c-10, address is 0x51 (7-bit address)
FAN ( EMC2301 ) on i2c-10, address is 0x2f (7-bit address)

If you need to add it to your program instead of the kernel, you can refer to the C and Python demo reference click here


sudo nano /boot/config.txt
 #Add the following lines at the end
 #Add # in front of dtparam=audio=on
 #Save and exit, restart
 sudo reboot

How to use Hwclock

Synchronize system clock to hardware clock

sudo hwclock -w

Synchronize hardware clock to system clock

sudo hwclock -s
 #The network or the NTP needs to be closed, otherwise it will be changed back.

Set the hardware clock time:

sudo hwclock --set --date="9/8/2021 16:45:05"

View hardware clock

sudo hwclock -r

Display version information

sudo hwclock --verbose


When powered on, the fan will spin for 1 second, then stop for 2 seconds, and then spin again, this is a normal phenomenon
There is no official configuration method for the fan currently , there is a third-party configuration method:
This method is published by a third party, and we are not responsible for any problems!

mkdir -p ~/src
 cd ~/src
 git clone
 cd cm4io-fan
 sudo chmod 777
 sudo ./
 #The following is a description of config.txt
 Name: cm4io-fan
 Info: Raspberry Pi Compute Module 4 IO Board fan controller
 Load: dtoverlay=cm4io-fan,<param>[=<val>]
 Params: minrpm RPM target for the fan when the SoC is below
                            mintemp (default 3500)
        maxrpm RPM target for the fan when the SoC is above
                            maxtemp (default 5500)
        midtemp Temperature (in millicelcius) at which the fan
                            begins to speed up (default 50000)
        midtemp_hyst Temperature delta (in millicelcius) below mintemp
                            at which the fan will drop to minrpm (default 2000)
        maxtemp Temperature (in millicelcius) at which the fan
                            will be held at maxrpm (default 70000)
        maxtemp_hyst Temperature delta (in millicelcius) below maxtemp
                            at which the fan begins to slow down (default 2000)

Or directly refer to the following:


The fan will start to accelerate when temperature is higher than 45 degrees Celsius, and will up to the highest speed when higher than 50 degrees Celsius.


CSI and DSI are disabled by default. When using the camera and DSI, it will occupy three I2C devices: I2C-10, I2C-11, and I2C-0.

  • Open a terminal and run the following commands:
 unzip -o -d ./CM4_dt_blob_Source
 sudo chmod 777 -R CM4_dt_blob_Source
 cd CM4_dt_blob_Source/
 #If you want to use both cameras and DSI0
 sudo  dtc -I dts -O dtb -o /boot/dt-blob.bin dt-blob-disp0-double_cam.dts
 #If you want to ue both cameras and DSI1
 sudo  dtc -I dts -O dtb -o /boot/dt-blob.bin dt-blob-disp1-double_cam.dts
 #When using any DSI interface, HDMI1 will have no image output, even if you do not connect the DSI screen, as long as you compile the corresponding file, then HDMI1 will not output
  #If you need to restore, please delete the corresponding dt-blob.bin: sudo rm -rf /boot/dt-blob.bin
  #After execution, turn off the power and restart the CM4

Recording test

And then connect the cameras and DSI display
1: Please power off the IO Board first before your connection.
2: Connect the power adapter after connecting the cameras and DSI display
3: Wait a few seconds before the screen boot up.
4: If the DSI LCD cannot display, please check if you have added /boot/dt-blob.bin. If there already has the dt-blob.bin, just try to reboot.
5: The camera needs to be enabled by raspi-config, enter sudo raspi-config on the terminal, choose Interfacing Options->Camera->Yes->Finish-Yes and reboot the system

Old Version (Buster)

  • Test the Cameras:

Test camera0:

sudo raspivid -t 0 -cs 0

Test camera1:

sudo raspivid -t 0 -cs 1

New Version (Bullseye)

If you are using the latest Raspberry Pi OS (Bullseye):

libcamera-hello -t 0

#The new system uses dual cameras
#Remove or comment out the line camera_auto_detect=1 in config.txt

#Add the following lines:

#Add the corresponding line according to the camera you use, where imx219 is the camera sensor model, and there are other sensors

#then restart

#Other parts of the commands:
#Check if the camera is detected
libcamera-hello --list-cameras

#Open the corresponding camera
libcamera-hello --camera 1
libcamera-hello --camera 0

#Taking Pictures
libcamera-jpeg -o test.jpg
#You can add --camera to specify the camera

More instructions click me

  • HDMI1 is disabled if you use DSI interfaces for displaying, even if you just compile the corresponding files without connecting to the DSI screen, please note it
  • Any connection of two HDMI ports can output images, not limited to which HDMI port, if two HDMI screens are connected, only HDMI0 has image output
  • If you want to enable both HDMI, please delete the dt-blob.bin file with the following command:
sudo rm -rf /boot/dt-blob.bin
  • Then reboot

Reference Raspberry Pi Manual



3D Drawing

Demo codes




a) Check whether dtparam -audio - on is blocked in /boot/config.txt

b) Check whether the /boot/dt-blob.bin file exists, if it cannot be used, delete it;


If you require technical support, please go to the Support page and open a ticket.