With the release of more flexible I/O support, the moteus controller auxiliary port can be used to monitor encoders using an onboard UART. Now, with firmware release 2023-02-01, those UART pins can be used as an arbitrary logic level serial port controlled by the application! Let’s see how to use it below.

First, you will need to look at the pin configuration table to find pins that support UART functionality, and configure them as UART in the “aux?.pins” configuration tree. Next, “aux?.uart.mode” should be set to “kTunnel”, along with the desired baud rate. That’s it on the configuration front.

To send and receive data from the serial port requires using the diagnostic mode CAN protocol. To date, diagnostic mode channel “1” has been used to send and receive diagnostic mode commands from moteus itself. Now two new channels are available:

• 2: aux1
• 3: aux2

Unfortunately, tview does not yet have support for these. However, the python library and moteus_tool do. If you are not running any moteus using application at the same time, you can start moteus_tool with “moteus_tool –console –diagnostic-channel 3” to send and receive data from the aux2 serial port rather than the normal moteus diagnostic protocol. Similarly, python applications can use the “moteus.Stream” class and specify an alternate channel, like:

c = moteus.Controller()
aux2_uart = moteus.Stream(c, channel=3)
await aux2_uart.write(b"Data to write on the aux2 UART pins")
print(await aux2_uart.readline())

That’s it for now, good luck!