> For the complete documentation index, see [llms.txt](https://wiki.cbunmanned.com/wiki/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://wiki.cbunmanned.com/wiki/products-eol/cbu-cm405-fc-eol/female-header-f405/uart.md).

# UART

**Serial Ports** (all mapped to the corresponding number, IE T4 R4 is Serial\_4)

1. Purple, Designated for the CM4 telemetry link using a male to male jumper. 
2. Brown, Designated for an external GPS, located next to I2C.
3. Blue, Free use
4. Orange, Free use
5. White, Serial 5 is shared with SBus in. If you are using a SBus Rx then Serial 5 is unavailable.

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