首先，在以前的工程中，通过ASF wizard 加入USART模块，再在ASF EXPLORER中打开API说明。
如下图所示：
然后按照指导形成程序：
最后编译通过，以下是执行结果
需要注意的是所有的管脚都在宏定义中定义：
所以要复管脚到别的引脚也得遵循这个宏定义：
/* ========== PORT definition for SERCOM3 peripheral ========== */
#define PIN_PA16D_SERCOM3_PAD0 16L /**< \brief SERCOM3 signal: PAD0 on PA16 mux D */
#define MUX_PA16D_SERCOM3_PAD0 3L
#define PINMUX_PA16D_SERCOM3_PAD0 ((PIN_PA16D_SERCOM3_PAD0 << 16) | MUX_PA16D_SERCOM3_PAD0)
#define PORT_PA16D_SERCOM3_PAD0 (1ul << 16)
#define PIN_PA22C_SERCOM3_PAD0 22L /**< \brief SERCOM3 signal: PAD0 on PA22 mux C */
#define MUX_PA22C_SERCOM3_PAD0 2L
#define PINMUX_PA22C_SERCOM3_PAD0 ((PIN_PA22C_SERCOM3_PAD0 << 16) | MUX_PA22C_SERCOM3_PAD0)
#define PORT_PA22C_SERCOM3_PAD0 (1ul << 22)
#define PIN_PA27F_SERCOM3_PAD0 27L /**< \brief SERCOM3 signal: PAD0 on PA27 mux F */
#define MUX_PA27F_SERCOM3_PAD0 5L
#define PINMUX_PA27F_SERCOM3_PAD0 ((PIN_PA27F_SERCOM3_PAD0 << 16) | MUX_PA27F_SERCOM3_PAD0)
#define PORT_PA27F_SERCOM3_PAD0 (1ul << 27)
#define PIN_PA17D_SERCOM3_PAD1 17L /**< \brief SERCOM3 signal: PAD1 on PA17 mux D */
#define MUX_PA17D_SERCOM3_PAD1 3L
#define PINMUX_PA17D_SERCOM3_PAD1 ((PIN_PA17D_SERCOM3_PAD1 << 16) | MUX_PA17D_SERCOM3_PAD1)
#define PORT_PA17D_SERCOM3_PAD1 (1ul << 17)
#define PIN_PA23C_SERCOM3_PAD1 23L /**< \brief SERCOM3 signal: PAD1 on PA23 mux C */
#define MUX_PA23C_SERCOM3_PAD1 2L
#define PINMUX_PA23C_SERCOM3_PAD1 ((PIN_PA23C_SERCOM3_PAD1 << 16) | MUX_PA23C_SERCOM3_PAD1)
#define PORT_PA23C_SERCOM3_PAD1 (1ul << 23)
#define PIN_PA18D_SERCOM3_PAD2 18L /**< \brief SERCOM3 signal: PAD2 on PA18 mux D */
#define MUX_PA18D_SERCOM3_PAD2 3L
#define PINMUX_PA18D_SERCOM3_PAD2 ((PIN_PA18D_SERCOM3_PAD2 << 16) | MUX_PA18D_SERCOM3_PAD2)
#define PORT_PA18D_SERCOM3_PAD2 (1ul << 18)
#define PIN_PA24C_SERCOM3_PAD2 24L /**< \brief SERCOM3 signal: PAD2 on PA24 mux C */
#define MUX_PA24C_SERCOM3_PAD2 2L
#define PINMUX_PA24C_SERCOM3_PAD2 ((PIN_PA24C_SERCOM3_PAD2 << 16) | MUX_PA24C_SERCOM3_PAD2)
#define PORT_PA24C_SERCOM3_PAD2 (1ul << 24)
#define PIN_PA19D_SERCOM3_PAD3 19L /**< \brief SERCOM3 signal: PAD3 on PA19 mux D */
#define MUX_PA19D_SERCOM3_PAD3 3L
#define PINMUX_PA19D_SERCOM3_PAD3 ((PIN_PA19D_SERCOM3_PAD3 << 16) | MUX_PA19D_SERCOM3_PAD3)
#define PORT_PA19D_SERCOM3_PAD3 (1ul << 19)
#define PIN_PA25C_SERCOM3_PAD3 25L /**< \brief SERCOM3 signal: PAD3 on PA25 mux C */
#define MUX_PA25C_SERCOM3_PAD3 2L
#define PINMUX_PA25C_SERCOM3_PAD3 ((PIN_PA25C_SERCOM3_PAD3 << 16) | MUX_PA25C_SERCOM3_PAD3)
#define PORT_PA25C_SERCOM3_PAD3 (1ul << 25)
以下是程序：
#include <asf.h>
struct usart_module usart_instance;
void configure_usart(void)
{
struct usart_config config_usart;
usart_get_config_defaults(&config_usart);
config_usart.baudrate = 9600;
config_usart.mux_setting = EDBG_CDC_SERCOM_MUX_SETTING;
config_usart.pinmux_pad0 = EDBG_CDC_SERCOM_PINMUX_PAD0;
config_usart.pinmux_pad1 = EDBG_CDC_SERCOM_PINMUX_PAD1;
config_usart.pinmux_pad2 = EDBG_CDC_SERCOM_PINMUX_PAD2;
config_usart.pinmux_pad3 = EDBG_CDC_SERCOM_PINMUX_PAD3;
while (usart_init(&usart_instance, EDBG_CDC_MODULE, &config_usart) != STATUS_OK)
{ }
usart_enable(&usart_instance);
}
int main (void)
{
/* Initialize the system and console*/
system_init();
configure_usart();
uint8_t string[] = "Hello World!\r\n";
usart_write_buffer_wait(&usart_instance, string, sizeof(string));
uint16_t temp;
while (true)
{
if (usart_read_wait(&usart_instance, &temp) == STATUS_OK)
{
while (usart_write_wait(&usart_instance, temp) != STATUS_OK) { } } }
}
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