BBB RS232 Cape RevB Getting Started

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This guide is intended to walk through the basic instructions on how to get your RS232 Cape working. If you have any question about this cape, please email

To purchase the Rs232 Cape please visit

To purchase the BeagleBone Black please visit

The instructions below are performed under following kernel and may vary for different kernel versions.

    root@beaglebone:~# uname -a
    Linux beaglebone 3.8.13-bone47 #1 SMP Fri Apr 11 01:36:09 UTC 2014 armv7l GNU/Linux

Default console UART

The RS232 Cape revision B supports UART0 (the console), UART1, UART2, and UART4. Users can choose between each UART port by moving the TX and RX jumpers on the PCB. By default, the RS232 cape is shipped with UART0 (the console) selected. Follow the instructions below to get the cape working:

  • Make sure the BB is powered off. Install the RS232 Cape on top of the BeagleBone Black. Ensure the 6-position female header of the cape aligned with the serial header J1 of the BBB.
  • Connect a serial cable to the D-Sub 9 connector on the RS232 Cape. Connect the other end of the serial cable to your PC. If you use something like this, ensure all the necessary drivers are installed.
  • Open a terminal window on your PC for the serial cable above.
  • SSH to your BBB via Ethernet or Ethernet-over-USB.
  • By default, UART0 should have been enabled; therefore, when powering up your BBB, you should see the boot messages on your PC serial terminal. Press Enter to check if the receiving line is working as well. You can now work with your BBB via the RS-232 connection.

Using other UART connections

UART1, UART2, and UART4 are not enabled by default. However, their device tree files are provided along with the production Debian software. To start using UART1, follow the instructions below:

  • Move the RX and TX jumpers on the RS232 Cape PCB to UART1 locations.
  • Inside your BBB terminal, enable the UART1 using capemgr:
    echo BB-UART1 > /sys/devices/bone_capemgr.*/slots
    cat /sys/devices/bone_capemgr.*/slots
        0: 54:PF--- 
        1: 55:PF--- 
        2: 56:PF--- 
        3: 57:PF--- 
        4: ff:P-O-L Bone-LT-eMMC-2G,00A0,Texas Instrument,BB-BONE-EMMC-2G
        5: ff:P-O-L Bone-Black-HDMI,00A0,Texas Instrument,BB-BONELT-HDMI
        7: ff:P-O-L Override Board Name,00A0,Override Manuf,BB-UART1
  • You should now see another ttyO device in /dev:
    ls /dev/ttyO*
        /dev/ttyO0  /dev/ttyO1
</syntaxhighlight lang="bash">
* Configure the new serial device:
<syntaxhighlight lang="bash">
    stty -F /dev/ttyO1 115200
  • You can now start writing or listening to RS232 connection via UART1. To output something out of UART1:
    echo hello > /dev/ttyO1

You should see the word "hello" shows up on your PC serial terminal. To listen to any input coming to UART1:

    cat /dev/ttyO1

Type something on the PC serial terminal and press Enter. You should see the result on BBB terminal window.