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The Raspberry Pi 4B has 6 Uart Pins. I want to use at least two of them but dont get them to work.

ls -al /dev/ttyAMA*

crw-rw---- 1 root dialout 204, 64 Oct 17 00:03 /dev/ttyAMA0

dmesg | grep tty

[    0.000000] Kernel command line: coherent_pool=1M 8250.nr_uarts=1 snd_bcm2835.enable_headphones=0 snd_bcm2835.enable_headphones=1 snd_bcm2835.enable_hdmi=1 snd_bcm2835.enable_hdmi=0 video=HDMI-A-1:1920x1080M@60 smsc95xx.macaddr=E4:5F:01:01:EA:DD vc_mem.mem_base=0xec00000 vc_mem.mem_size=0x10000000  console=tty1 root=PARTUUID=8acf4fd7-02 rootfstype=ext4 fsck.repair=yes rootwait
[    0.000882] printk: console [tty1] enabled
[    1.576439] fe201000.serial: ttyAMA0 at MMIO 0xfe201000 (irq = 36, base_baud = 0) is a PL011 rev2
[    1.589642] fe215040.serial: ttyS0 at MMIO 0xfe215040 (irq = 37, base_baud = 62500000) is a 16550
[    3.502245] systemd[1]: Created slice system-getty.slice.

dtoverlay -a | grep uart

  midi-uart0
  midi-uart1
  midi-uart2
  midi-uart3
  midi-uart4
  midi-uart5
  miniuart-bt
  qca7000-uart0
  uart0
  uart1
  uart2
  uart3
  uart4
  uart5

Here the /boot/config.txt

[all]
enable_uart=1              # Enable the UART subsystem
#dtoverlay=pi3-disable-bt    # Disable Bluetooth if you want to use UART0
#dtoverlay=uart0            # Enable UART0
dtoverlay=uart1            # Enable UART1
dtoverlay=uart2            # Enable UART2
dtoverlay=uart3            # Enable UART3
dtoverlay=uart4            # Enable UART4
dtoverlay=uart5            # Enable UART5
michael86
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1 Answers1

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See Raspberry Pi4 UART

I use enable_uart=1 and dtoverlay=uart2 to enable UARTs on my Pi4. (UART2 requires disabling HAT EPROM).

enable_uart=1 enables /dev/ttyS0; use /dev/serial0 for normal UART on GPIO14/15.

Many of the entries you listed do nothing (or are incompatible); only enable the UART you want to use.

Milliways
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