PineNote Development/UART

This page contains information on creating and using a UART dongle for the PineNote. The PineNote was shipped with a compatible UART dongle, but replacements are not available to order in case of loss or hardware fault. Thankfully it is not difficult to make your own from easily-acquired components.

A PineNote UART dongle enables you to:

1. Interact with the system boot menu
2. Read system events in real time as the PineNote is used
3. Fix the PineNote without opening the case if something goes wrong while flashing it

Since the PineNote is an embedded system, interfacing with it during boot is more complicated than with an ordinary computer. The UART dongle enables you to do this.

Creating your own UART dongle

A PineNote UART dongle has four components:

1. A USB-C breakout board with a male connector exposing the 24 pins of the PineNote's female USB-C port (located on the bottom of the device)
2. A USB-UART adapter, to plug into a USB port of the computer you'll use to interface with the PineNote
3. Jump wires to connect specific breakout board pins to pins on the USB-UART adapter
4. Electrical tape to wrap connectors and prevent shorts

The PineNote's internal UART system is documented in this schematic. USB-C pins are documented on the USB-C Wikipedia page; of the 24 pins, two are designated for "side band" use. These pins are labeled SBU1 (A8) and SBU2 (B8). In the PineNote UART schematic you can see (on the bottom right diagram) these pins are given the label UART2_TX_SUB1 and UART2_RX_SUB2 respectively. The first (TX) is used for transmitting data and the second (RX) is used for receiving data. These are the pins which must be exposed by the breakout board.

There are many possible USB-C breakout board designs available for purchase online. One particularly useful design is a "passthrough" or "intercept" style, with both male and female USB-C ports. This design is more versatile in case you want to reuse it in other projects, and also enables you to connect to the PineNote via UART and USB at the same time. An example of this product can be found here, although you are encouraged to shop around for cheaper options.

Similarly, there are many USB-UART designs available. These devices plug into your computer and expose a number of pins themselves, connecting to specific pins on the breakout board with jump wires. Here is one example with jump wires included, although you are again encouraged to shop around for alternatives.

Once you have acquired all necessary components, assemble the UART dongle as follows:

1. Connect a jump wire from the GND pin on the USB-UART adapter to one of the four GND pins on the USB-C breakout board (A1, A12, B1, or B12)
2. Connect a jump wire from the RXD pin on the USB-UART adapter to the UART2_RX_SUB2 pin on the USB-C breakout board (SBU2 aka B8)
3. Connect a jump wire from the TXD pin on the USB-UART adapter to the UART2_TX_SUB2 pin on the USB-C breakout board (SBU1 aka A8)

Test that your system works by following the use instructions down below. Be very careful not to touch or short the pins while current is flowing through them - this can damage your device! Once you have confirmed that your UART dongle works, wrap all metal connectors in electrical tape to prevent accidental shorts.