Access UART ports
Universal Asynchronous Receiver Transmitters (UARTs) are commonly found in embedded devices and are built into the mother board of mobile devices. For developers working on the Linux kernel and the lower levels of the operating system, UART ports can be used to make the development easier. For example, the UART ports are used for the following tasks:
- Observing boot and debug messages
- Kernel development
- Interacting with the system via a shell
On this page, you find instructions for how to access them on a range of Xperia devices. However, note that this is strictly for developers only, and you should be aware of the risks involved in unlocking the boot loader of your device. In addition, to access the UART port, you need to solder on the motherboard of your device, which means that you risk to permanently damage the motherboard.
To be able to follow this guide, you need a multimeter tool, a soldering station and a magnifying glass. You also need to have SMD soldering skills, as well as hardware hacking and advanced kernel debugging knowledge.
Note: Although protocol compatible, RS-232 and UART are not voltage compatible. UARTs most commonly operate at 3.3 volts, but can also be found operating at other standard voltages (for example 1.8V). This means that you will have to use an UART to USB adapter which can be acquired online. Any TTL232RG 1V8 adapter can be used to connect to the phone.
Identifying and connecting to the right pins
Find your device in the table below, and locate the header on your device and the header pinout for pinout reference.
The first thing we want to do is perform a continuity test between ground and possible ground pins on the connector using the multimeter. This will tell us which pin is connected directly to ground. Metal shielding is a convenient ground point to use for testing. Placing one probe on a shield and touching the other to pin 3, the multimeter emits a continuous audible tone, indicating that pin 3 is connected to ground. This will show you the connector orientation. After ground pin is identified use it as a reference for the RX and TX pins. Please note that the UART RX pin is for Data To Mobile Station and UART TX is for Data From Mobile Station.
After the pins are indentified we recommend that you solder 0.5 mm insulated wires to each of them and glue a connector on the device. This way the UART to USB adapter can be used on multiple devices.