Helios64 has one UEXT (Universal-Extension-Connector) header which exposes 3 serial communication interfaces into a single header:

* I2C
* SPI
* RS232 (UART)

![P2 Location](/helios64/img/uext/uext.jpg)

## Pinout Table

![P2 Pinout](/helios64/img/uext/uext_pinout.jpg)

Below is the full pinout of the UEXT header:

| PIN | Port | Remarks |
|-----|------|-------------|
| 1 | 3.3V | |
| 2 | GND | |
| 3 | TXD (UART) | |
| 4 | RXD (UART) | |
| 5 | SCL (I2C) | |
| 6 | SDA (I2C) | |
| 7 | MISO (SPI) | |
| 8 | MOSI (SPI) | |
| 9 | SCK (SPI) | |
|10 | SSEL (SPI) | |

!!! Warning
    Be careful with the header polarity when connecting.

## SPI & I2C

Refer to the respective pages directly:

- [SPI](/helios64/hardware/)
- [I2C](/helios64/i2c/)

## RS232 (UART)

The UART bus exposed on the UEXT header is the same than the RK3399 SoC serial console exposed on the USB Type-C. There is no dedicated UART bus on the UEXT connector. The intention is to allow user to connect to SoC serial console by another way than the USB-to-Serial bridge.

!!! Important
    If you connect some modules which might require dedicated serial UART line to the SoC, this module will not operate properly.