Overview

The UART parameter group (specifically within AP_Periph) configures the physical serial ports on peripheral hardware.

Key Concepts

1. Serial Mapping

On DroneCAN nodes, UARTs are used to connect GPS receivers or ADS-B units.

UARTx_OPTIONS: Bitmask for signal inversion and swapping.
UARTx_RTSCTS: Enables hardware flow control.

Developer Notes

Library: Tools/AP_Periph.
See Also: SERIAL for the main autopilot serial configuration.

UART0_OPTIONS

UART 0 Serial Options

Default 0

Range 0 15

UART 0 Serial Options (UART0_OPTIONS)

Description

UART0_OPTIONS (usually appearing as SERIAL0_OPTIONS) provides low-level electrical control over the primary communication port.

This is often used when connecting the flight controller to non-standard hardware that requires specific signal logic.

Bit 0 (1): Invert RX. Flips the high/low logic for receiving.
Bit 1 (2): Invert TX. Flips the high/low logic for transmitting.
Bit 2 (4): Half-Duplex. Combines TX and RX onto a single wire (One-Wire mode).
Bit 3 (8): Swap Pins. Swaps the RX and TX functionality (Requires STM32 F7/H7).

Tuning & Behavior

Default: 0.
Usage: Only change if your external hardware (like an RC receiver or specialized sensor) explicitly requires it.
Reboot Required: Yes.

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UART 0 Flow Control (UART0_RTSCTS)

Description

UART0_RTSCTS enables Hardware Flow Control for the primary serial/USB port.

It is functionally identical to UART1_RTSCTS.

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Serial options

Note: This parameter functions identically to SERIAL1_OPTIONS.

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UART 1 Flow Control (UART1_RTSCTS)

Description

UART1_RTSCTS enables Hardware Flow Control for the first telemetry port.

Flow control uses two extra wires (RTS and CTS) to signal when a device is ready to receive data. This prevents "Buffer Overflows" where one device sends data faster than the other can process it, which would otherwise result in corrupted or missing telemetry.

0: Disabled.
1: Enabled.
2: Auto (Default). The autopilot will attempt to detect if the connected device supports flow control.

Tuning & Behavior

Recommendation: Leave at 2 (Auto).
SiK Radios: These radios support hardware flow control. If you have the RTS/CTS wires connected, this setting will ensure maximum data reliability.

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