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Helios64 has one UEXT (Universal-Extension-Connector) header which exposes 3 serial communication interfaces into a single header:
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* I2C
* SPI
* RS232 (UART)
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## Pinout Table
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Below is the full pinout of the UEXT header:
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| PIN | Port | Remarks |
|-----|------|-------------|
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| 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) | |
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!!! Warning
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Be careful with the header polarity when connecting.
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## SPI & I2C
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Refer to the respective pages directly:
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- [SPI ](/helios64/hardware/ )
- [I2C ](/helios64/I2C/ )
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## RS232 (UART)
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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.
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!!! Important
If you connect some modules which might require dedicated serial UART line to the SoC, this module will not operate properly.
