The Raspberry Pi UARTs
RPi Serial Connection
STICKY: Pi3 UART stopped working? Read this.
PL011 UART => wireless/Bluetooth module mini UART => Linux console output PL011 UART => /dev/ttyAMA0 mini UART => /dev/ttyS0 Linux console => /dev/serial0 => primary UART mini UART => core frequency of the VPU on the VC4 GPU VPU frequency change => baud rate of the UART also changes config.txt => enable_uart=1 /boot/cmdline.txt => console=serial0,115200
BCM2835 ARM Peripherals (PDF)
cmdline.txt dwc_otg.lpm_enable=0 console=serial0,115200 console=tty1 root=PARTUUID=20586949-02 rootfstype=ext4 elevator=deadline fsck.repair=yes rootwait config.txt enable_uart=1