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The UART application enables an external microcontroller or computer to control and monitor the VESC over a serial UART connection using the VESC communication protocol. This is the default application (APP_UART) so the UART port remains available for firmware updates immediately after flashing.

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Port assignments

The firmware supports up to three UART ports, selected by the UART_PORT enum: 
typedef enum {
    UART_PORT_COMM_HEADER = 0,  // 7/8-pin COMM connector (default)
    UART_PORT_BUILTIN,          // Built-in BLE module UART
    UART_PORT_EXTRA_HEADER      // Third hardware UART (if present)
} UART_PORT;
UART_PORT_COMM_HEADER (index 0) is the standard external-access port and the one to use when connecting a Raspberry Pi, Arduino, or other host controller.

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Baud rate

The default baud rate is 115200 bps, defined in appconf_default.h: 
#define APPCONF_UART_BAUDRATE    115200
You can change this in VESC Tool under App Settings → UART or call app_uartcomm_configure at runtime: 
void app_uartcomm_configure(
    uint32_t baudrate,
    bool permanent_enabled,
    UART_PORT port_number
);
Setting permanent_enabled to true keeps the UART port active even when another application is selected.
The APPCONF_PERMANENT_UART_ENABLED default is true, which means UART communication with VESC Tool remains available regardless of which application is active.

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Communication protocol

The VESC UART protocol uses length-prefixed packets with a CRC16 checksum. Each packet has the structure:
FieldSizeDescription
Start byte1–2 bytes0x02 for short packets (≤255 bytes), 0x03 for long.
Length1–2 bytesPayload length.
PayloadN bytesCommand byte followed by command-specific data.
CRC162 bytesCRC over the payload.
Stop byte1 byte0x03.
The packet framing is handled by the packet module. The application thread calls commands_process_packet for each complete received packet.

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Serial configuration

From app_uartcomm.c, the UART is configured with standard 8N1 framing and LIN break detection: 
SerialConfig uart_cfg = {
    BAUDRATE,         // 115200 by default
    0,
    USART_CR2_LINEN,  // LIN mode / break detection
    0
};

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Runtime API

void app_uartcomm_initialize(void);
void app_uartcomm_start(UART_PORT port_number);
void app_uartcomm_stop(UART_PORT port_number);
void app_uartcomm_send_packet(
    unsigned char *data,
    unsigned int len,
    UART_PORT port_number
);

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Combining with other applications

If you need analog or PPM input and UART telemetry simultaneously, use the combined modes:
  • APP_PPM_UART — PPM input with UART active.
  • APP_ADC_UART — ADC input with UART active.
In these modes the UART port handles communication with VESC Tool while the physical input signal drives the motor.

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Wiring

The VESC UART pins operate at 3.3 V logic. Do not connect a 5 V UART directly without a level shifter, as this will damage the hardware.
Connect your host controller to the COMM header:
COMM pinSignal
TXVESC transmit → host RX
RXVESC receive ← host TX
GNDCommon ground
5V / 3.3VOptional power supply

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