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Freigegebene technische Dokumentation veröffentlicht; Text-only und noindex

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'''Documentation notice:''' This technical documentation was independently rewritten from an archived supplier source. Check technical details and commands against the product version and manufacturer documentation before use.

== Summary ==
The CM4-ETH-RS485-BASE-B is an expansion board for the Raspberry Pi Compute Module 4. It provides two Ethernet ports (one Gigabit RJ45 and one USB-based 100M Ethernet), four isolated RS485 interfaces, two CSI camera ports, HDMI output, and various configuration options via jumpers and config.txt.

== Related products at JW Tech ==
* [https://shop.jw-tech.eu/p/WSAL21666 WSAL21666 – Dual ETH Quad RS485 Base Board (B) for Raspberry Pi Compute Module 4, Gigabit Ethernet, 4CH Isolated RS485]
* [https://shop.jw-tech.eu/p/WSAL22239 WSAL22239 – Dual ETH Mini-Computer For Raspberry Pi Compute Module 4(NOT Included), Gigabit Ethernet, 4CH Isolated RS485]
* [https://shop.jw-tech.eu/p/WSAL22555 WSAL22555 – Dual ETH Mini-Computer For Raspberry Pi Compute Module 4(NOT Included), Gigabit Ethernet, 4CH Isolated RS485]

== Technical overview ==
* Expansion board for Raspberry Pi Compute Module 4; supports 7–36 V DC power or 5 V via Type-C
* Four isolated RS485 interfaces with 5.08 mm pitch; mode switching via 0R resistors (full-auto/semi-auto)
* Two Ethernet ports: ETHERNET0 (Gigabit RJ45) and ETHERNET1 (USB-based 100M Ethernet)
* Two MIPI CSI camera ports (CAM0/CAM1); single cameras work only on CAM0
* HDMI0 output supports 4K@30fps
* RTC connection via I2C (address 0x51, bus i2c-10); requires dtparam=i2c_vc=on in config.txt
* Fan connector: 4-wire, 5V fans only, PWM control via GPIO18 without speed sensing
* Encryption chip ATSHA204 present, disabled by default
* USB2.0 disabled by default; enable via dtoverlay=dwc2,dr_mode=host in config.txt
* Boot switch: ON = boot over USB Type-C (programming), OFF = boot from eMMC/Micro-SD

'''Commands and examples – verify before use:'''
<syntaxhighlight lang="text">
sudo nano /boot/config.txt
dtoverlay=dwc2,dr_mode=host
sudo nano /boot/config.txt
dtoverlay=uart3
dtoverlay=uart4
dtoverlay=uart5
sudo raspi-config
# Interface Options -> Serial Port -> Yes
dtparam=i2c_vc=on
#dtparam=audio=on
sudo wget https://files.waveshare.com/upload/4/42/PCF85063_code.7z
7z x PCF85063_code.7z -O./
cd PCF85063_code/c
sudo make clean && sudo make -j 8 && sudo ./main
cd python/example
sudo python3 main.py
wget https://files.waveshare.com/upload/d/d1/CM4-ETH-RS485-BASE-B-Example.zip
unzip CM4-ETH-RS485-BASE-B-Example.zip -d ./CM4-ETH-RS485-BASE-B-Example
cd CM4-ETH-RS485-BASE-B-Example/FAN/python
sudo python3 FAN.py
sudo raspivid -t 0 -cs 0
sudo rpi-update
</syntaxhighlight>

== Notes and version constraints ==
* Do not plug or unplug devices while powered on, except USB and HDMI
* Verify fan voltage before connecting – only 5V fans are supported
* When flashing the image via Type-C, do not connect other devices to ensure stable power
* CM4 requires 5V/2A during normal operation; otherwise automatic shutdowns or clock throttling may occur
* Switching RS485 modes requires physically changing the 0R resistors on the back side
* DSI displays are not available on this board – only HDMI0
* Single cameras work only on the CAM0 port
* RTC I2C detection can fail if dtparam=audio=on is blocking it or if dt-blob.bin is faulty

== Source and revision record ==
* [https://www.waveshare.com/wiki/CM4-ETH-RS485-BASE-B CM4-ETH-RS485-BASE-B - Waveshare Wiki]
* Source revision: 104318
* Captured: 2026-09-03T03:14:13+00:00
* SHA-256: <code>5861dd8657dcb6eb0762a2875f5a282ffa99ca20dd34e6b0b820ef26eb12e737</code>

WSAL21666 – CM4-ETH-RS485-BASE-B/en - Versionsgeschichte

JWTechPublisher: Freigegebene technische Dokumentation veröffentlicht; Text-only und noindex