兩機通訊可以使用MODBUS來實現
大部分的PLC都提供有MODBUS方便指令的,可以直接呼叫的,只是簡單的設定幾個特殊暫存器就ok。大部分的編成工作還是在微控制器上,MODBUS通訊有兩種通訊格式1)ASCII 2)RTU
1.ASCII模式 當控制器設為在Modbus網路上以ASCII(美國標準資訊交換程式碼)模式通訊,在訊息中的每個8Bit位元組都作為一個ASCII碼(兩個十六進位制字元)傳送。這種方式的主要優點是字元傳送的時間間隔可達到1秒而不產生錯誤。 程式碼系統 · 十六進位制,ASCII字元0...9,
A...F
兩機通訊可以使用MODBUS來實現
大部分的PLC都提供有MODBUS方便指令的,可以直接呼叫的,只是簡單的設定幾個特殊暫存器就ok。大部分的編成工作還是在微控制器上,MODBUS通訊有兩種通訊格式1)ASCII 2)RTU
1.ASCII模式 當控制器設為在Modbus網路上以ASCII(美國標準資訊交換程式碼)模式通訊,在訊息中的每個8Bit位元組都作為一個ASCII碼(兩個十六進位制字元)傳送。這種方式的主要優點是字元傳送的時間間隔可達到1秒而不產生錯誤。 程式碼系統 · 十六進位制,ASCII字元0...9,
A...F
· 訊息中的每個ASCII字元都是一個十六進位制字元組成 每個位元組的位 · 1個起始位 · 7個數據位,最小的有效位先發送 · 1個奇偶校驗位,無校驗則無 1個停止位(有校驗時),2個Bit(無校驗時) 錯誤檢測域 · LRC(縱向冗長檢測) 2、RTU模式 當控制器設為在Modbus網路上以RTU(遠端終端單元)模式通訊,在訊息中的每個8Bit位元組包含兩個4Bit的 十六進位制字元。這種方式的主要優點是:在同樣的波特率下,可比ASCII方式傳送更多的資料。 程式碼系統 8位二進位制,十六進位制數0...9,A...F
訊息中的每個8位域都是一個兩個十六進位制字元組成 每個位元組的位 1個起始位 8個數據位,最小的有效位先發送 1個奇偶校驗位,無校驗則無 1個停止位(有校驗時),2個Bit(無校驗時) 錯誤檢測域 CRC(迴圈冗長檢測) CRC域是兩個位元組,包含一16位的二進位制值。它由傳輸裝置計算後加入到訊息中。接收裝置重新計算收到訊息的CRC,並與接收到的CRC域中的值比較,如果兩值不同,則有誤。 CRC是先調入一值是全“1”的16位暫存器,然後呼叫一過程將訊息中連續的8位位元組各當前暫存器中的值進行處理。僅每個字元中的8Bit資料對CRC有效,起始位和停止位以及奇偶校驗位均無效。 CRC產生過程中,每個8位字元都單獨和暫存器內容相異或(XOR),結果向最低有效位方向移動,最高有效位以0填充。LSB被提取出來檢測,如果LSB為1,暫存器單獨和預置的值或一下,如果LSB為0,則不進行。整個過程要重複8次。在最後一位(第8位)完成後,下一個8位位元組又單獨和暫存器的當前值相或。最終暫存器中的值,是訊息中所有的位元組都執行之後的CRC值。 CRC新增到訊息中時,低位元組先加入,然後高位元組。 CRC簡單函式如下: unsigned short CRC16(puchMsg,usDataLen) unsigned char *puchMsg ; /* 要進行CRC校驗的訊息*/ unsigned short usDataLen ; /* 訊息中位元組數*/ { unsigned char uchCRCHi = 0xFF ; /* 高CRC位元組初始化*/ unsigned char uchCRCLo = 0xFF ; /* 低CRC 位元組初始化*/ unsigned uIndex ; /* CRC迴圈中的索引*/ while (usDataLen--) /* 傳輸訊息緩衝區*/ { uIndex = uchCRCHi ^ *puchMsgg++ ; /* 計算CRC */ uchCRCHi = uchCRCLo ^ auchCRCHi[uIndex] ; uchCRCLo = auchCRCLo[uIndex] ; } return ((uchCRCHi << 8) | uchCRCLo) ; } /* CRC 高位位元組值表*/ static 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 } ; /* CRC低位位元組值表*/ static 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 } ;