Pin Diagrams

BeagleBone Black

P9 Header

P8 Header

Mode

In order to use a non-default system mode, you both need to change the mode during initialization, and you will also need to change the hardware configuration. This is done by editing /boot/uEnv.txt, and uncommenting the relevant lines, as below:

SystemMode	Affected Systems
DEFAULT	No changes
NO_STORAGE	Disable eMMC
NO_HDMI Disable	HDMI and HDMI Audio
NO_EXPANSION	Disable eMMC, HDMI, and HDMI Audio

Before you can use any I/O system on the BBB, you need to call BeagleBone.Initialize() once in your program.
This takes two arguments, the first one being the SystemMode as above (note that changing this doesn't change anything other than not making Scarlet error if you try to use a reserved pin. It doesn't make that pin work!) The second argument is "UseFastMode". I recommend you leave this as true unless you run into I/O issues.

This switches between memory mapped I/O (true), and filesystem-based I/O (false).
Filesystem-based I/O is the "correct" Linux way to do it, so is therefore more supported. Memory mapping is several orders of magnitude faster (Up to 1000x!), but is not technically supported. That said, it almost always works fine.

PWM

The BeagleBone only has 6 actual PWM outputs, divided into 3 devices.
Each device (0, 1, 2) is completely independent.
Each device has two outputs (A, B). These outputs run off the same clock, and at the same frequency, but their duty cycle is controlled independently.
Each output goes to two different physical pins if enabled as such in setup. They are tied together, so even if you connect two different things to the two pins named "1_A", the output will be identical at all times. The only reason there are two pins is so that you can still use the PWM output if you are using one of the pins for another task (such as SPI), or if it assigned to a pin used by HDMI/eMMC.

SPI

You will need to select GPIO pins as chip-select lines. The built-in CS lines (e.g. SPI0_CS0) are not used.

CAN

CAN bus 0 may not work. I recommend using 1 instead.

UART

Avoid UART3 for now.

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Raspberry Pi

UART

By default, the UART pins are used to communicate with the Bluetooth radio, and as such cannot function. You can disable Bluetooth, and enable UART, by following this procedure (untested, source):
sudo nano /boot/config.txt
At the end of the file, add:
dtoverlay=pi3-disable-bt
Disable Bluetooth:
sudo systemctl disable hciuart
Reboot.