Template:2-CH UART TO ETH Spec

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  • Embedded Ethernet MAC and PHY layers
  • Bi-direction transparent data transmission between UART and Ethernet
  • 10/100M, full-duplex/half-duplex auto-negotiation Ethernet interface, 802.3-compliant
  • Auto-MDI/MDIX, detect and switch cable type automatically
  • Supports DHCP auto-obtained IP and DNS domain access
  • Network parameter configuration like chip operating mode, port, IP, via host computer software or UART command
  • 2-CH UART concurrent operation, standalone transparent transmission for each channel
  • Full-duplex or half-duplex UART communication supports RS485 RX/TX auto switch
  • Supports virtual serial port software (provided)
  • KEEPALIVE mechanism support


  • Operating voltage:3.3V/5V
  • Operating current: 140mA
  • Operating mode: TCP/UDP
  • UART baud rate: 300bps !921.6Kbps
  • UART TTL level: 3.3V/5V compatible
  • Storage temperature: -55°C ~ 125°C
  • Operating temperature: -40°C ~ 85°C
  • Dimensions: 53.00 x 22.00mm


5V/3V3 power positive, use any pin of 5V/3.3V pins for power supply
GND ground
RST1 external reset input, low active
RESET restore to factory setting, detected when chip power on, low active
TXD1 asynchronous UART 1 data output (enabled by default)
TXD2 asynchronous UART 2 data output (disabled by default)
RXD1 asynchronous UART 1 data input (enabled by default)
RXD2 asynchronous UART 2 data input (disabled by default)
CFG0 UART config mode, low level to enter configuration, high level to exit configuration
RUN Operating status indicating pin
DIR1 UART 1 RS485 RX/TX switch (connects to external RS485 controller)
DIR2 UART 2 RS485 RX/TX switch (connects to external RS485 controller)


CH9121 is a network serial port transparent transmission chip, which can realize the two-way transparent transmission of serial data and network data. It supports 4 working modes of TCP CLIENT/SERVER, UDP CLIENT/SERVER, and the serial port baud rate support range is 300bps~921600bps, which needs to be configured before use. The host computer software NetModuleConfig.exe or serial command configures the network parameters and serial parameters of the chip. After the configuration is completed, CH9121 will saves the configuration parameters to the internal storage space. After the chip is reset, CH9121 will work according to the saved configuration values.

Default configuration

The UART2 is disabled, UART1 works in TCP CLIENT mode by default. The default setting of ETH is as below:

  • Device IP:
  • Subnet Mask:
  • Gateway:
  • Device Port: 2000
  • Target IP:
  • Target port: 1000

The default setting of the UART1 is as below:

  • Baud rate: 9600
  • Timeout: 0
  • data bit: 8
  • Stop bit: 1
  • Parity: None
  • Clearing buffer: Never