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Helios64 has one UEXT (Universal-Extension-Connector) header which exposes 3 serial communication interfaces into a single header:
* I2C
* SPI
* RS232 (UART)
## Pinout Table
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/ )
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- [I2C ](/helios64/i2c/ )
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## RS232 (UART)
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The UART exposed on the UEXT header is UART Controller 0 from the RK3399 SoC. The primary purpose of this UART is to provide serial communication between SoC and Device connected to the UEXT port.
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!!! Note
If you are looking for SoC serial console you should refer to [USB-C Console Mode ](/helios64/usb/#serial-console ).
