Hi @RobertCNelson 
My BAD !!! I should not based on the file name under /dev ! 
I should use dmseg | grep tty…that will show the available TTY ! Now both UART_1 & 3 work perfectly!
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Hi @RobertCNelson My BAD !!! I should not based on the file name under /dev ! I should use dmseg | grep tty…that will show the available TTY ! Now both UART_1 & 3 work perfectly!