CentOS5.4 Linux下Modbus TCP IP协议C++的一个小例子

////////////////////////////////////////////////////////////////////////////*ReadCoils函数：读继电器的状态 ， 成功返回ture。send 数据长度=12recv 数据长度=10unsigned short int addr 读继电器的起始地址(继电器编号-1) 。注意：1~8个继电器，起始地址从0开始unsigned short int len 读取继电器的个数，最大8.debug_state 如果为1 打印出调式信息ubool *paraDO 读出的继电器状态SOCKET s_bnc,fd_set fds,timeval tv 是辅助的网络接口参数*////////////////////////////////////////////////////////////////////////////inline bool ReadCoils(unsigned short int addr, byte & coilstate, SOCKET_INT s_bnc){cmd_len = 12;byte cmd_code = 1; //命令代码：01，读继电器byte *cmd_string ;byte *echo_string ;cmd_string = new byte[cmd_len] ;echo_string = new byte[cmd_len] ;cmd_string[ 0] = 0 ; // modbus 协议规定标示cmd_string[ 1] = 0 ;cmd_string[ 2] = 0 ;cmd_string[ 3] = 0 ;cmd_string[ 4] = 0 ; // length 高位部分 命令的后续字节数量cmd_string[ 5] = 6 ; // length 低位部分 命令的后续字节数量cmd_string[ 6] = 0 ; // Unit Identifier :identification of a remote slave connected on a serial line or on other buses.cmd_string[ 7] = cmd_code ;cmd_string[ 8] = (unsigned char) (addr >> 8);cmd_string[ 9] = (unsigned char) addr;cmd_string[10] = 0; //(unsigned char) (len >> 8);cmd_string[11] = 8; //(unsigned char) len ;int iret;fd_set fds;struct timeval tv;tv.tv_sec = SLEEP ; //超时等待时tv.tv_usec = 0;FD_ZERO(&fds);FD_SET(s_bnc, &fds);/* wait for permission to send(等待是否可写write)*/iret = select(s_bnc +1, NULL, &fds, NULL, &tv); /*write*/if (iret=0){ if(debug_state) printf("Timer over!n"); close(s_bnc); return false ;}else if (iret<0){if(debug_state) printf("select is err! n");close(s_bnc);return false ;}/*send 写入数据 */iret = send(s_bnc, (char *)cmd_string, cmd_len , 0);if (iret < cmd_len){if(debug_state) printf("failed to send chars:%dn",iret);close(s_bnc);return false;}/*wait for response(等待是否可读read)*/FD_SET(s_bnc, &fds);iret = select(s_bnc +1 , &fds, NULL, NULL, &tv);if (iret=0){if(debug_state) printf("Timer over!n");close(s_bnc);return false ;}else if (iret<0){if(debug_state) printf("select is err! n");close(s_bnc);return false ;}/*读出数据 */iret = recv(s_bnc, (char *)echo_string, 12 , 0);if (iret<=0){if(debug_state) printf("接受数据recv语句出错n");}if ( echo_string[7] == cmd_code) /*7位置是命令*/{/*if(debug_state) printf("n读数据成功了n");*/}else if ( echo_string[7] == (0x80 | cmd_code)){if(debug_state) printf("设备主动报告:操作出错n");return false;}else{if(debug_state) printf("出错n");return false;}//int nDOFlag = echo_string[9] |echo_string[10] << 8); //9位置10位置是继电器的状态//unsigned char nDOFlag = echo_string[9]; //因为E3018只有8个继电器,故没有10位置coilstate = echo_string[9];delete []cmd_string;delete []echo_string;return true;}

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