USB-TTL console logic level voltage

Hi @theJoker8814,

I understand you're encountering a boot issue with your GS1920-24HPv2 switch, where the SYS LED blinks green, and you're looking to use the 4-pin console connector for troubleshooting. You're specifically asking about the logic level voltage for the RX/TX pins on this connector.

For Zyxel devices, including switches, the USB-to-TTL serial adapters generally operate at a 3.3V logic level.

Here's a guide to help you establish a console connection and gather more information:

• Console Cable Pinout:

  • The 4-pin console connector on Zyxel switches typically has the following pin configuration: Pin 1 (with a circle mark) is usually Not Available (NA), Pin 2 is White (RX), Pin 3 is Green (TX), and Pin 4 is Black (GND).
  • Important: Do not connect the red power pin from your USB-TTL cable to any Zyxel console pin.
  • When connecting your USB-TTL adapter, ensure you connect the Transmit (TX) of the USB adapter to the Receive (RX) of the switch's console, and the Receive (RX) of the USB adapter to the Transmit (TX) of the switch's console. Connect Ground (GND) to Ground.

• USB-TTL Adapter Voltage:

  • The USB-TTL device needs to be set to 3.3V. This is often done with a jumper on the adapter.

• Terminal Emulator Settings:

  • Once connected, use a terminal emulator program (like PuTTY or Tera Term).
  • Configure the serial connection with the following settings:
    • Speed (Baud Rate): 115200 bps
    • Data Bits: 8
    • Parity: None
    • Stop Bits: 1
    • Flow Control: None (or Off)

• Troubleshooting Steps:

  • Connect the console cable, open your terminal emulator, and then power on the switch. You should see boot messages scrolling in the terminal.
  • If you see repeated PoE errors in the console log, it might indicate a hardware issue with the switch's PoE modules, potentially requiring an RMA.
  • If the switch eventually boots to a state where you can access the GUI, collect the tech-support files from Management > Maintenance > Tech-Support > All.

To further assist you, please provide the following information:

• Detailed Network Topology: A diagram showing how your GS1920-24HPv2 is connected to other devices in your network.
• Screenshots: If possible, please provide screenshots of the output you receive in the terminal emulator once you establish the console connection.
• Firmware Version: If you can eventually access the GUI or retrieve it from the console logs, please provide the firmware version currently on the switch.