5 485 uart 接收多个字节出错

发布于 2022-09-30 15:01:40 浏览：665 订阅该版

使用官方给的UART例程移植到自己板子上，使用uart2,调试口使用jlinkRtt，mcu stm32f103zet6
软件环境：rt_thread studio2.2.5
硬件环境：自己做的板子上暂时跑一个uart2连接金升阳TD321S485模块，
实验现象：用官方给的例子实现接收和发送，在不加485模块时，接收多少个数据，即可发出多少个，但是接上485之后，在接收一个字节时，发出的数据正确，接收多个字节，发出数据报错，这是什么原因？

```c
/*
 * Copyright (c) 2006-2022, RT-Thread Development Team
 *
 * SPDX-License-Identifier: Apache-2.0
 *
 * Change Logs:
 * Date           Author       Notes
 * 2022-09-13     RT-Thread    first version
 */

#include <rtthread.h>
#include <drivers/pin.h>
#include <rtdbg.h>
#include <led.h>
#include <rtdevice.h>
#include "gpio.h"
#include "usart.h"
//#include <serial.h
#define SAMPLE_UART_NAME "uart2"
static struct rt_semaphore rx_sem;
static rt_device_t serial;
#define RS485_TX_EN 1
struct serial_configure config = RT_SERIAL_CONFIG_DEFAULT; /* 初始化配置参数 */
int RS485_TX(void)
{

rt_pin_write(RS485_TX_EN, PIN_LOW);
    return 0;
}

int RS485_RX(void)
{

rt_pin_write(RS485_TX_EN, PIN_HIGH);
    return 0;
}
int RS485_INIT(void)
{

rt_pin_mode(RS485_TX_EN, PIN_MODE_OUTPUT);
    RS485_RX();
    return 0;
}

/* 接收数据回调函数 */
static rt_err_t uart_input(rt_device_t dev, rt_size_t size)
{
    /* 串口接收到数据后产生中断，调用此回调函数，然后发送接收信号量 */
    rt_sem_release(&rx_sem);

return RT_EOK;
}
static void serial_thread_entry(void *parameter)
{
    char ch;

while (1)
    {
        /* 从串口读取一个字节的数据，没有读取到则等待接收信号量 */
        while (rt_device_read(serial, -1, &ch, 1) != 1)
        {
            /* 阻塞等待接收信号量，等到信号量后再次读取数据 */
            rt_sem_take(&rx_sem, RT_WAITING_FOREVER);
        }
        /* 读取到的数据通过串口错位输出 */
        ch = ch;
        RS485_TX();
        rt_device_write(serial, 0, &ch, 1);
        RS485_RX();
    }
}

static int uart_sample()
{
    rt_err_t ret=RT_EOK;
    char uart_name[RT_NAME_MAX];
    char str[]="this a rtthread example!\r\n";
/*    if (argc == 2)
     {
         rt_strncpy(uart_name, argv[1], RT_NAME_MAX);
     }
     else
     {
         rt_strncpy(uart_name, SAMPLE_UART_NAME, RT_NAME_MAX);
     }*/
    serial=rt_device_find(SAMPLE_UART_NAME);

if(!serial)
    {
        rt_kprintf("find %s failed!\n",uart_name);
        return RT_ERROR;
    }
    config.baud_rate=BAUD_RATE_9600;
    if(RT_EOK != rt_device_control(serial, RT_DEVICE_CTRL_CONFIG, &config))
    {
        rt_kprintf("配置串口设备失败\n");
        return RT_ERROR;
    }
    rt_kprintf("配置串口设备成功!\n");
    RS485_INIT();
    rt_sem_init(&rx_sem, "rx_sem", 0, RT_IPC_FLAG_FIFO);
    rt_device_open(serial, RT_DEVICE_FLAG_INT_RX);
    rt_device_set_rx_indicate(serial, uart_input);
    RS485_TX();
    rt_device_write(serial, 0, str, (sizeof(str)-1));
    RS485_RX();
    rt_thread_t thread =rt_thread_create("serial", serial_thread_entry, RT_NULL, 1024, 25, 10);
    if(thread!=RT_NULL)
    {
        rt_thread_startup(thread);
    }
    else {
        ret=RT_ERROR;
    }
    return ret;

}

int main(void)
{
    uart_sample();
    led_init();
    while (1)
    {
        led_toggle();
       rt_thread_mdelay(1000);
    }
    return RT_EOK;
}

```

图1用UART直接发送，用uart转usb接到电脑显示如下

![用uart发送.png](https://oss-club.rt-thread.org/uploads/20220930/d08c8e4ac4bff7e793db9a841283e6dc.png "用uart发送.png")
图2，用485直接发送，用485转usb接到电脑显示如下

![485接收发送.png](https://oss-club.rt-thread.org/uploads/20220930/e10a19ca48dc4d48302f3b0c494cb8b1.png "485接收发送.png")