Quick start guide for the SAM USART module

This is the quick start guide for the USART module, with step-by-step instructions on how to configure and use the driver in a selection of use cases.

The use cases contain several code fragments. The code fragments in the steps for setup can be copied into a custom initialization function, while the steps for usage can be copied into, e.g., the main application function.

Note

Some SAM devices contain both USART and UART modules, with the latter being a subset in functionality of the former but physically separate peripherals. UART modules are compatible with the USART driver, but only for the functions and modes supported by the base UART driver.

USART use cases

• Basic use case - transmit a character
• USART receive character and echo back
• USART receive character and echo back via interrupts

Note

The USART pins configuration are not included here. Please refer the related code in board_init() function.

Basic use case - transmit a character

In this use case, the USART module is configured for:

• Using USART0
• Baudrate: 9600
• Character length: 8 bit
• Parity mode: Disabled
• Stop bit: None
• RS232 mode

Setup steps

Prerequisites

1. System Clock Management (sysclock)
2. Common IOPORT API (ioport)

Example code

The following configuration must be added to the project (typically to a conf_usart.h file, but it can also be added to your main application file.)

#define USART_SERIAL                 USART0
#define USART_SERIAL_ID              ID_USART0  //USART0 for sam4l
#define USART_SERIAL_BAUDRATE        9600
#define USART_SERIAL_CHAR_LENGTH     US_MR_CHRL_8_BIT
#define USART_SERIAL_PARITY          US_MR_PAR_NO
#define USART_SERIAL_STOP_BIT        US_MR_NBSTOP_1_BIT

Add to application initialization:

    sysclk_init();
 
    board_init();
 
    const sam_usart_opt_t usart_console_settings = {
        USART_SERIAL_BAUDRATE,
        USART_SERIAL_CHAR_LENGTH,
        USART_SERIAL_PARITY,
        USART_SERIAL_STOP_BIT,
        US_MR_CHMODE_NORMAL
    };
#if SAM4L
  sysclk_enable_peripheral_clock(USART_SERIAL);
#else
    sysclk_enable_peripheral_clock(USART_SERIAL_ID);
#endif
    usart_init_rs232(USART_SERIAL, &usart_console_settings,
            sysclk_get_main_hz());
    usart_enable_tx(USART_SERIAL);
    usart_enable_rx(USART_SERIAL);

Workflow

1. Initialize system clock:

   sysclk_init();

2. Configure the USART Tx and Rx pins by call the board init function:

   board_init();

   Note

   Set the following define in conf_board.h file to enable COM port,it will be used in board_init() function to set up IOPorts for the USART pins. For SAM4L:

   #define CONF_BOARD_COM_PORT

   For other SAM devices:

   #define CONF_BOARD_UART_CONSOLE

3. Create USART options struct:

   const sam_usart_opt_t usart_console_settings = {
        USART_SERIAL_BAUDRATE,
        USART_SERIAL_CHAR_LENGTH,
        USART_SERIAL_PARITY,
        USART_SERIAL_STOP_BIT,
        US_MR_CHMODE_NORMAL
   };

4. Enable the clock to the USART module:

     #if SAM4L
     sysclk_enable_peripheral_clock(USART_SERIAL);
   #else
       sysclk_enable_peripheral_clock(USART_SERIAL_ID);
   #endif

5. Initialize the USART module in RS232 mode:

   usart_init_rs232(USART_SERIAL, &usart_console_settings,
           sysclk_get_main_hz());

6. Enable the Rx and Tx modes of the USART module:

   usart_enable_tx(USART_SERIAL);
   usart_enable_rx(USART_SERIAL);

Usage steps

Example code

Add to application C-file:

usart_putchar(USART_SERIAL, 'a');

Workflow

1. Send an 'a' character via USART

   usart_putchar(USART_SERIAL, 'a');