Nucleof446 UART

[harry123]

• Im trying to communicate between nucleof446re board with other processor board using UART.
• Communication works fine when I connect my nucleo board with USB power supply but when I connect nucleo with external 3.3V or 5V supply the communication does not happen.
• Can I know what might be the reason. I have connect Tx Rx and GND of both the boards. 

Thank You

[KnarfB]

Is the MCU running at all, eg blinking a LED? If the ST-LINK is not powered up, it may keep the MCU in reset.

If you are using Tx, Rx, and GND pins directly from the MCU pins (Nucleo board connectors), there is not much else what could fail. Electrical levels? Clock generation? A scope would come in handy here.

Guess you already found the board schematics NUCLEO-F446RE - STM32 Nucleo-64 development board with STM32F446RE MCU, supports Arduino and ST morpho connectivity - STMicroelectronics 

hth

KnarfB

[Peter BENSCH]

@harry123 this NUCLEO gets its clock for HSE from MCO of the onboard debugger (ST-LINK/V2-1). However, if you are not supplying the NUCLEO from USB, but separately, you would have to provide an alternative clock. To do this, you can either use an internal clock or solder a crystal to X3 plus the associated R, C and solder bridges SB (see UM1724, section 6.7).

Hope that helps?

Good luck
/Peter