UART

Edge 2 has two general-purpose UART connectors, UART3 and UART5, for serial devices such as sensors, GPS receivers and microcontrollers. Both are four-pin, 2.0 mm connectors on the top side of the board: UART3 next to the MASKROM button, and UART5 on the edge beside the coin-cell holder.

Figure 1. The UART3 and UART5 connectors

Specifications

• 3.3 V logic. Do not connect 5 V logic directly.
• 3.3 V supply output on pin 1, up to 100 mA

Pin Assignments

Both connectors use the same layout.

Pin#	PinName	PinType	Input/Output	Signal Description
1	3.3V	Power	Output	3.3 V supply, 100 mA maximum
2	UART3_RX / UART5_RX	signal	Input	Receive data
3	UART3_TX / UART5_TX	signal	Output	Transmit data
4	GND	Power	NA	Power and signal reference ground

Wiring

Connect the device's GND to pin 4, its TX to RX (pin 2), and its RX to TX (pin 3). If the device has its own power supply, leave pin 1 unconnected.

Figure 2. Wiring a USB to TTL converter to UART3 or UART5

Test the UART with Mixtile OS

This test sends text between Edge 2 and a computer through a USB to TTL converter wired as in Figure 2. In Mixtile OS, UART3 is /dev/ttyS3 and UART5 is /dev/ttyS5. The examples use UART5.

1. On the computer, open the converter's serial port at 115200 baud, for example with picocom as in Connect to Edge 2:

   Host PC

   picocom -b 115200 /dev/ttyUSB0

2. On Edge 2, set the same speed and send a line:

   Edge 2

   stty -F /dev/ttyS5 115200 raw -echo
   echo "hello from Edge 2" > /dev/ttyS5

   Expected result: hello from Edge 2 appears in picocom.

3. To receive, run the following on Edge 2 and type in picocom:

   Edge 2

   cat /dev/ttyS5

   Expected result: what you type appears on Edge 2. Press Ctrl+C to stop.

note

This procedure has not yet been verified on Edge 2 hardware with Mixtile OS.