谈谈最近学习Modbus协议的真实感受

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我是靠谱客的博主重要可乐，最近开发中收集的这篇文章主要介绍谈谈最近学习Modbus协议的真实感受，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

Modbus通讯协议

Modbus是一种串行通信协议，是Modicon公司（现在的施耐德电气 Schneider Electric）于1979年为使用可编程逻辑控制器（PLC）通信而发表。Modbus已经成为工业领域通信协议的业界标准（De facto），并且现在是工业电子设备之间常用的连接方式。

Modbus常用的传输方式与格式（RTU/ASCII/TCP）

这里就说说RTU模式，其他的没用到

Modbus功能码

modbus完整支持很多功能码，但是实际在应用的时候常用的也就那么几个。具体如下：

任务
STM32串口Modbus通信（基于LiteOS操作系统）

功能部分程序

Modbus接收处理

        // Modbus通讯->接收处理
		u16 uiDelayGet = 0;
		len = Read_Comm(COM1,Buf,100);
		if(len > 0)
		{
			for(int i=0;i<len;i++)
			{
				Dispose_Modbus(Buf[i],&uiDelayGet);
				if(uiDelayGet >= 100 && uiDelayGet <= 10000)//范围判断
				{
					uiDelayTime = uiDelayGet;
					Debug_Printf("task3->{%d}获取到上位设定延时时间=%drn",cur_tick,uiDelayTime);
				}
			}
			pre_tick = LOS_TickCountGet();
		}
		int iTimeLen = cur_tick - pre_tick;
		if(iTimeLen > 2000)
		{
			g_step = 0;
			pre_tick = LOS_TickCountGet();
			cur_tick = LOS_TickCountGet();
		}
		
		// 每5秒定时请求上位,正式系统采用Modbus发送处理
		u32 uTemp = LOS_Tick2MS(cur_tick);
		if(uTemp-pre_sendTick >= 5000)
		{
			pre_sendTick = uTemp;
			Debug_Printf("task3->{%d}向上位请求时间参数->rn",cur_tick);
		}

Modbus接收部分：

//Modbus接收部分，假定03功能码，00寄存器（变量为*pDelayTime）
void Dispose_Modbus(u8 ucRece,u16 *pDelayTime)
{
	*pDelayTime = 0;
	switch(g_step)
	{
		case 0:
			g_receLen = 0;
			g_arrRece[g_receLen++] = ucRece;
			g_step = 2;
			break;
		case 2:
			g_arrRece[g_receLen++] = ucRece;
			if(g_receLen == 8)
			{
				//crc 校验
				Debug_Printf("接收到数据包：rn");
				for(int i=0;i<g_receLen;i++)
				{
					Debug_Printf("%02x ",g_arrRece[i]);
				}
				u16 uiCrc = CRC16(g_arrRece, 6);
				if(uiCrc == g_arrRece[6]*256+g_arrRece[7])//校验和相等
				{
					*pDelayTime = g_arrRece[4]*256+g_arrRece[5];
					Debug_Printf("CRC 校验通过！，参数设定=%drn",*pDelayTime);
				}
				else
				{
					Debug_Printf("CRC 校验失败！rn");
				}
			}
			break;
	}
}

CRC校验部分

/* Table of CRC values for high–order byte */
static const unsigned char auchCRCHi[] = {
0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81,
0x40, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0,
0x80, 0x41, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01,
0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41,
0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81,
0x40, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0,
0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01,
0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40,
0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81,
0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0,
0x80, 0x41, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01,
0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41,
0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81,
0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0,
0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01,
0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81, 0x40, 0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41,
0x00, 0xC1, 0x81, 0x40, 0x01, 0xC0, 0x80, 0x41, 0x01, 0xC0, 0x80, 0x41, 0x00, 0xC1, 0x81,
0x40
};
/* Table of CRC values for low–order byte */
static const char  auchCRCLo[] = {
0x00, 0xC0, 0xC1, 0x01, 0xC3, 0x03, 0x02, 0xC2, 0xC6, 0x06, 0x07, 0xC7, 0x05, 0xC5, 0xC4,
0x04, 0xCC, 0x0C, 0x0D, 0xCD, 0x0F, 0xCF, 0xCE, 0x0E, 0x0A, 0xCA, 0xCB, 0x0B, 0xC9, 0x09,
0x08, 0xC8, 0xD8, 0x18, 0x19, 0xD9, 0x1B, 0xDB, 0xDA, 0x1A, 0x1E, 0xDE, 0xDF, 0x1F, 0xDD,
0x1D, 0x1C, 0xDC, 0x14, 0xD4, 0xD5, 0x15, 0xD7, 0x17, 0x16, 0xD6, 0xD2, 0x12, 0x13, 0xD3,
0x11, 0xD1, 0xD0, 0x10, 0xF0, 0x30, 0x31, 0xF1, 0x33, 0xF3, 0xF2, 0x32, 0x36, 0xF6, 0xF7,
0x37, 0xF5, 0x35, 0x34, 0xF4, 0x3C, 0xFC, 0xFD, 0x3D, 0xFF, 0x3F, 0x3E, 0xFE, 0xFA, 0x3A,
0x3B, 0xFB, 0x39, 0xF9, 0xF8, 0x38, 0x28, 0xE8, 0xE9, 0x29, 0xEB, 0x2B, 0x2A, 0xEA, 0xEE,
0x2E, 0x2F, 0xEF, 0x2D, 0xED, 0xEC, 0x2C, 0xE4, 0x24, 0x25, 0xE5, 0x27, 0xE7, 0xE6, 0x26,
0x22, 0xE2, 0xE3, 0x23, 0xE1, 0x21, 0x20, 0xE0, 0xA0, 0x60, 0x61, 0xA1, 0x63, 0xA3, 0xA2,
0x62, 0x66, 0xA6, 0xA7, 0x67, 0xA5, 0x65, 0x64, 0xA4, 0x6C, 0xAC, 0xAD, 0x6D, 0xAF, 0x6F,
0x6E, 0xAE, 0xAA, 0x6A, 0x6B, 0xAB, 0x69, 0xA9, 0xA8, 0x68, 0x78, 0xB8, 0xB9, 0x79, 0xBB,
0x7B, 0x7A, 0xBA, 0xBE, 0x7E, 0x7F, 0xBF, 0x7D, 0xBD, 0xBC, 0x7C, 0xB4, 0x74, 0x75, 0xB5,
0x77, 0xB7, 0xB6, 0x76, 0x72, 0xB2, 0xB3, 0x73, 0xB1, 0x71, 0x70, 0xB0, 0x50, 0x90, 0x91,
0x51, 0x93, 0x53, 0x52, 0x92, 0x96, 0x56, 0x57, 0x97, 0x55, 0x95, 0x94, 0x54, 0x9C, 0x5C,
0x5D, 0x9D, 0x5F, 0x9F, 0x9E, 0x5E, 0x5A, 0x9A, 0x9B, 0x5B, 0x99, 0x59, 0x58, 0x98, 0x88,
0x48, 0x49, 0x89, 0x4B, 0x8B, 0x8A, 0x4A, 0x4E, 0x8E, 0x8F, 0x4F, 0x8D, 0x4D, 0x4C, 0x8C,
0x44, 0x84, 0x85, 0x45, 0x87, 0x47, 0x46, 0x86, 0x82, 0x42, 0x43, 0x83, 0x41, 0x81, 0x80,
0x40
} ;

/*puchMsg message to calculate CRC upon */
/*usDataLen quantity of bytes in message */
unsigned short CRC16(unsigned char *puchMsg, unsigned short usDataLen)
{
	unsigned char uchCRCHi = 0xFF ; /* high byte of CRC initialized */
	unsigned char uchCRCLo = 0xFF ; /* low byte of CRC initialized */
	unsigned uIndex ; /* will index into CRC lookup table */
	while (usDataLen --) /* pass through message buffer */
	{
		uIndex = uchCRCHi ^ *puchMsg++ ; /* calculate the CRC */
		uchCRCHi = uchCRCLo ^ auchCRCHi[uIndex] ;
		uchCRCLo = auchCRCLo[uIndex] ;
	}
	return (uchCRCHi << 8 | uchCRCLo) ;
}