单片机通过Modbus协议与HMI通信

如何用单片机通过MODBUS协议与HMI通信Modbus简介Modbus协议最初由Modicon公司开发出来，在1979年末该公司成为施耐德自动化（SchneiderAutomation）部门的一部分，现在Modbus已经是工业领域全球最流行的协议。此协议支持传统的RS-232、RS-422、RS-485和以太网设备。许多工业设备，包括PLC，DCS，智能仪表等都在使用Modbus协议作为他们之间的通讯标准。Modbus协议包括ASCII、RTU、TCP等，并没有规定物理层。Modbus的ASCII、RTU协议规定了消息、数据的结构、命令和就答的方式，数据通讯采用Maser/Slave方式，Master端发出数据请求消息，Slave端接收到正确消息后就可以发送数据到Master端以响应请求；Master端也可以直接发消息修改Slave端的数据，实现双向读写。Modbus协议需要对数据进行校验，串行协议中除有奇偶校验外，ASCII模式采用LRC校验，RTU模式采用16位CRC校验。ASCII协议和RTU协议相比拥有开始和结束标记，因此在进行程序处理时能更加方便，而且由于传输的都是可见的ASCII字符，所以进行调试时就更加的直观，另外它的LRC校验也比较容易。但是因为它传输的都是可见的ASCII字符，RTU传输的数据每一个字节ASCII都要用两个字节来传输，比如RTU传输一个十六进制数0xF9,ASCII就需要传输’F’’9’的ASCII码0x39和0x46两个字节，这样它的传输的效率就比较低。所以一般来说，如果所需要传输的数据量较小可以考虑使用ASCII协议，如果所需传输的数据量比较大，最好能使用RTU协议。ModBus消息帧使用ASCII模式，消息以冒号（：ASCII码3AH）开始，以回车换行（ASCII码0DH,0AH）符结束。其它域可以使用的传输字符0...9,A...F。网络上的设备不断侦测：字符，当有一个冒号接收到时，每个设备都解码下个域（地址域）来判断是否发给自己的。消息中字符间发送的时间间隔最长不能超过1秒，否则接收的设备将认为传输错误。个典型消息帧如下所示：模式起始地址功能数据校验结束ASCII:设备地址功能代码起地址数据数数据数据nLRC高字节LRC低字节<CR>例如:0603006B0003使用RTU模式，两个消息间至少要有3.5个字符时间的停顿间隔，整个消息帧必须作为一连续的流转输，如果在帧完成之前有超过1.5个字符时间的停顿时间，接收设备将假定下一字节是一个新消息的地址域。同样，如果一个新消息在小于3.5个字符时间内接着前个消息开始，接收的设备将会认为它是前一消息的延续。这将导致一个错误，所以每一帧间的间隔必须大于3.5个字符时间,而在一帧内每个数据间隔不应大于1.5个字符时间.模式起始地址功能数据校验结束RTU(4T)设备地址功能代码起地址数据数数据数据nCRC高字节CRC低字节(4T)例如0603006B0003三.参考程序：下面以MCS-51单片机作为ModbusRTU从站与eViewMD204L通信例子.联接方式通信按RS232可RS485方式联接.通信速率为19200，数据位为8位,停止位1位，无校验.MD204L选用ModbusRTU协议，按相同方式设置好通信参数.工作原理MCU处理事务的过程中，串口处于侦听状态，当收到数据时，启动计时器，在发现一个大于3.5T的间隔后，判断报文的地址域是否与本身的设备地址一致，如果是的话，对收到的缓冲区内容进行校验,如果通过校验则认为是一个合法的Modbus报文帧，对该报文进行解释，并产生回送报文.示例报文发出：010400020001900A解释：01为站号,0002为起地址,0001为长度(1个字)回复：0104021000B4F0解释：01为回复站,02为字节数,1000为数据参考程序如下对MCU串口进行设置voidprotocol_init(void){//波特率19200，8，1，odd//都用工作方式3，不需要第9位时就将TB8赋1SCON=0xD0;〃工作方式3PCON&=0X7F;〃确保smod1=0;TMOD=0x21;//0x21,timer1,mode2,timer0mode1TH1=0xfd;TR1=1;//TR1:timer1run〃超时等待3.5个字符位以判断帧结束。〃则3.5个字符至多需要12*3.5=42个位，就是42*stop_timest2_time_out=(signedchar)TH1*(42*6);if(!(PCON&0x80))t2_time_out<<=1;T2CON=0;T2MOD=0;TR1=1;//TR1:timer1run〃超时等待3.5个字符位以判断帧结束。TI=0;RI=0;EA=1;ES=1;prepare_recv();}初始化接收状态的函数如下voidprepare_recv(void)small{〃准备接收TR2=0;//初始化T2ET2=1;T2REG=RCAP2=t2_time_out;receiving=1;frame_timeout=0;recv_index=0;recv_error=0;RW485=Rs485Rx;REN=1;}串行通信中断处理程序voidprotocol_serial_process(void)small{unsignedchartmp;if(_testbit_(TI)){trans_index++;〃下一个字节if(trans_index<protocol.buff_len){format_trans_send();//按约写的规格发送一个字节}else{trans_finished=1;prepare_recv();//发送完毕,转为接收状态}}if(_testbit_(RI)){RI=0;if(receiving){TH2=RCAP2H;〃重新装载计时器，等侍3.5T的中断TR2=1;tmp=SBUF;CommBuf[recv_index++]=tmp;if(recv_index>=BUF_MAX_LEN){//帧越界，出错，重收receiving=0;recv_error=1;}}T2定时器用于作为帧结束判断定时器，当发生中断时，意味已经有超过了3.5T的间隔voidtimer2(void)interrupt5〃计时中断2，用于帧超时计时{TR2=0;TF2=0;if(receiving){receiving=0;receive_finished=1;if((recv_index>7)&&(CommBuf[0]==protocol.device_addr)&&(!recv_error)){〃如果与当前设备地址一致并且报文长度有效，则报文进一步分析protocol.buff_len=recv_index;TH2=RCAP2H=DELAY_TIME_H;TL2=RCAP2L=DELAY_TIME_L;ET2=1;TR2=1;REN=0;}elseprepare_recv();〃否则丢弃这次接收，重新开始}else{{if(!recv_error){AnalyzeRecieve();//分析并生成回复报文send_frame_comm();//开始回复报文，按设定的参数格式进行发送}elseprepare_recv();}}}校验采用CRC校验,函数代码如下/*TableOfCRCValuesforhigh-orderbyte*/unsignedcharcodeauchCRCHi[]={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,

TOC\o"1-5"\h\z0x40,0x01,0xC0,0x80,0x41,0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,0x01,0xC0,0x80,0x41,0x00,0xC1,0x81,0x40,0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,0x01,0xC0,0x80,0x41,0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,0x00,0xC1,0x81,0x40,0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,0x01,0xC0,0x80,0x41,0x00,0xC1,0x81,0x40,0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,0x01,0xC0,0x80,0x41,0x00,0xC1,0x81,0x40,0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,0x01,0xC0,0x80,0x41,0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,0x00,0xC1,0x81,0x40,0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,0x01,0xC0,0x80,0x41,0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,0x00,0xC1,0x81,0x40,0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,0x01,0xC0,0x80,0x41,0x00,0xC1,0x81,0x40,0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,0x01,0xC0,0x80,0x41,0x00,0xC1,0x81,0x40}；/*TableofCRCvaluesforlow-orderbyte*/unsignedcharcodeauchCRCLo[]={TOC\o"1-5"\h\z0x00,0xC0,0xC1,0x01,0xC3,0x03,0x02,0xC2,0xC6,0x06,0x07,0xC7,0x05,0xC5,0xC4,0x04,0xCC,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,0x