开发板：LP-MSPM0L1306 LaunchPad
例程说明：通过短接TX和RX的引脚，让TX的数据直接发送到RX引脚上，来实现串口发送和接收的例程。使用FIFO的方式实现串口的发送和接收。如果发送和接收都完成，用户LED会闪烁，如果发送和接收没完成，用户LED常亮。
开发板的操作：需要断开J101上TXD和RXD与XDS110-ET下载板的连接，短接TXD与RXD。
例程分析：
1、首先是串口的配置，波特率照常配置，只需要使能FIFO，以及配置发送和接收FIFO的长度即可
2、代码如下所示：
#include "ti_msp_dl_config.h"
/*
* Configure the internal loopback mode.
* Note that data received on the UART RXD IO pin will be ignored when
* loopback is enabled.
*/
#define ENABLE_LOOPBACK_MODE true
/*
* Number of bytes for UART packet size
* The packet will be transmitted by the UART.
* This example uses FIFOs with polling, and the maximum FIFO size is 4.
* Refer to interrupt examples to handle larger packets.
*/
#define UART_PACKET_SIZE (4)
/* Delay for 5ms to ensure UART TX is idle before starting transmission */
#define UART_TX_DELAY (160000)
/* Data for UART to transmit */
uint8_t txPacket[UART_PACKET_SIZE] = {'M', 'S', 'P', '!'};
/* Data received from UART */
uint8_t rxPacket[UART_PACKET_SIZE];
int main(void)
{
SYSCFG_DL_init();//系统初始化
/* Optional delay to ensure UART TX is idle before starting transmission */
delay_cycles(UART_TX_DELAY);
/* Set LED to indicate start of transfer */
DL_GPIO_clearPins(GPIO_LEDS_PORT, GPIO_LEDS_USER_LED_1_PIN);
/* Fills TX FIFO with data and transmits the data */
DL_UART_Main_fillTXFIFO(UART_0_INST, &txPacket[0], UART_PACKET_SIZE);//填充数据发送数组并发送数据
/* Wait until all bytes have been transmitted and the TX FIFO is empty */
while (DL_UART_Main_isBusy(UART_0_INST))//等待数据发送完毕
;
/*
* Wait to receive the UART data
* This loop expects UART_PACKET_SIZE bytes
*/
for (uint8_t i = 0; i < UART_PACKET_SIZE; i++) {
rxPacket[i] = DL_UART_receiveDataBlocking(UART_0_INST);
}//循环接收发送的数据到接收缓存区，因为TX和RX对接了
/* If write and read were successful, toggle LED */
//假如发送和接收成功的话，才会进去下面的while循环
while (1) {
DL_GPIO_togglePins(GPIO_LEDS_PORT,
GPIO_LEDS_USER_LED_1_PIN | GPIO_LEDS_USER_TEST_PIN);
delay_cycles(5000000);
}
}
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