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WSAL20655 – 2-CH UART TO ETH/en

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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 Waveshare 2-CH UART TO ETH module links two serial TTL interfaces to a 10/100 Mbps Ethernet port via the CH9121 chip. It supports four operating modes — TCP client, TCP server, UDP client and UDP server — as well as bidirectional transparent transmission between UART and Ethernet.

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Technical overview

  • Operating voltage 3.3 V or 5 V; typical current draw about 140 mA.
  • Two independent UART channels: channel 1 is enabled by default, channel 2 is disabled by default.
  • Ethernet: 10/100 Mbps full/half-duplex with auto-negotiation, 802.3-compliant, automatic MDI/MDIX detection.
  • Four network operating modes: TCP CLIENT, TCP SERVER, UDP CLIENT, UDP SERVER.
  • Default values: IP 192.168.1.200, subnet mask 255.255.255.0, gateway 192.168.1.1, device port 2000, target IP 192.168.1.100, target port 1000.
  • UART1 defaults: 9600 baud, 8 data bits, 1 stop bit, no parity, timeout 0, buffer never cleared.
  • Pins: 5V/3V3, GND, RST1 (external reset, low active), RESET (factory settings on power-on, low active), TXD1/RXD1 (enabled), TXD2/RXD2 (disabled), CFG0 (low enters configuration mode), RUN (status indicator), DIR1/DIR2 (RS485 RX/TX switching).
  • Configuration is done via the PC software NetModuleConfig.exe or through serial commands; stored parameters are restored after a reboot.
  • The CH9121 stores its configuration in internal memory; after a reset the chip operates according to the saved values.
  • Demo projects for microcontrollers such as Raspberry Pi Pico, Arduino or STM32 are provided in C and Python; connections use the respective GPIO pins.

Commands and examples – verify before use:  

sudo apt-get install p7zip-full
sudo wget https://files.waveshare.com/upload/3/37/2-CH_UART_TO_ETH_CODE.7z
7z x Pico_ETH_CH9121_CODE.7z -o./2-CH UART TO ETH_CODE
cmake ..
make -j9
cp main.uf2 /media/pi/RPI-RP2/

Notes and version constraints

  • The listed default IP values are factory presets; before deployment in your own network, the IP configuration must be adapted to the local subnet.
  • The demo files must be downloaded and extracted; the exact Pico firmware version (rp2-pico-20210418-v1.15.uf2) is version-sensitive.
  • When flashing the Pico over USB, the BOOTSET button must be held until the drive is recognized — otherwise the firmware will not be written.
  • When using RS485, the DIR1/DIR2 pins must be connected to an external RS485 control circuit; without it, the automatic switching remains unused.
  • The Thonny version must be up to date, because older versions may lack the Pico support package.
  • Before production operation, packet loss at higher baud rates should be tested.

Source and revision record

  • 2-CH UART TO ETH - Waveshare Wiki
  • Source revision: 102648
  • Captured: 2026-09-02T04:08:37+00:00
  • SHA-256: 0590b7c8e72e86009bb912160691ccb362ab76f109664387400464f027ba38e0
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