Portenta X8 + Breakout Board - Serial Monitor Blank / UART0 Only Works with Serial1, Not Serial

[dhruvi_suthar]

Hi @b707,

• The Arduino Serial Monitor will not open automatically when I upload code to the Portenta X8.

• If I open it manually, it stays completely blank (I’ve attached the snapshot below).
  

  
  
  However, when I connect a CP2102C USB-to-UART converter to UART0 on the Breakout Board, I can see the logs in TeraTerm — but in that case, it will not accept any keyboard input.
  
  
  
  One more interesting thing:

• If I switch from UART0 to UART2 (or any other UART), I get an error.
  

  

• While looking into the core files (pins_arduino.h and Serial.cpp), I noticed that Serial is hardcoded to use UART1 and all other UART instances are blocked because of this line:

#define SERIAL_HOWMANY 1

This seems to limit the number of accessible hardware Serial instances. Because of that, any other UART besides UART1 isn’t usable through Serial.

Right now, I’m stuck on what’s the correct way to:

1. Map Serial to the UART I want, or
2. Increase SERIAL_HOWMANY so I can use more than one hardware UART — but those files are read-only, so I can’t just edit them directly.
   
   
   
   
   

Do you know if it’s safe to override this setting, or if there’s an official way to remap the Serial ports on the Portenta X8?

Thanks in advance!