我的PLC用的是官方庫(kù)：Modbus Rtu Slave(3.1)
波特率是9600，無校驗(yàn)，Port0

功能碼：05 設(shè)置單個(gè)繼電器狀態(tài)（強(qiáng)制離散輸出位）
QB0對(duì)應(yīng)數(shù)據(jù)地址 00 00----00 07
QB1 對(duì)應(yīng)數(shù)據(jù)地址 00 08----00 0F
QB2 對(duì)應(yīng)數(shù)據(jù)地址 00 10----00 07
FF 00是輸出高電平
00 00 是輸出低電平

舉例說明：
PC----PLC
     發(fā)送：03 05 00 00 FF 00 8D D8
             03：從站地址，PLC地址，類型BYTE
             05：功能碼，設(shè)置單個(gè)繼電器狀態(tài)（強(qiáng)制離散輸出位），類型BYTE
             00 00：設(shè)置地址，類型WORD
             FF 00：設(shè)置狀態(tài)，類型WORD
         FF 00 Q0.0 = 1;
         00 00 Q0.0 = 0
FC 28: CRC校驗(yàn)；類型WORD
PLC---PC
     接受：03 05 00 00 FF 00 8D D8
             03：從站地址，PLC地址，類型BYTE
             01：功能碼，設(shè)置單個(gè)繼電器狀態(tài)（強(qiáng)制離散輸出位），類型BYTE
             00 00 : 設(shè)置地址，類型WORD
             FF 00 ：設(shè)置狀態(tài)，類型WORD
             FF 00 Q0.0 = 1;
         00 00 Q0.0 = 0
            3D E2: CRC校驗(yàn)；類型WORD

通過以上的實(shí)例你可以用各種語(yǔ)言編寫控制程序，通過串口控制plc

附上c語(yǔ)言編寫CRC16校驗(yàn)程序
這個(gè)是查表的方法






/* CRC 高位字節(jié)值表 */
const uchar 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低位字節(jié)值表*/
const uchar 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
} ;


/******************************************************************
功能: CRC16校驗(yàn)
輸入:
輸出:
******************************************************************/
uint crc16( uchar *puchMsg, uint usDataLen )
{
    uchar uchCRCHi = 0xFF ; // 高CRC字節(jié)初始化
    uchar uchCRCLo = 0xFF ; // 低CRC 字節(jié)初始化
    unsigned long uIndex ;         // CRC循環(huán)中的索引

    while ( usDataLen-- )     // 傳輸消息緩沖區(qū)
    {
        uIndex = uchCRCHi ^ *puchMsg++ ;     // 計(jì)算CRC
        uchCRCHi = uchCRCLo ^ auchCRCHi[uIndex] ;
        uchCRCLo = auchCRCLo[uIndex] ;
    }

    return ( uchCRCHi << 8 | uchCRCLo ) ;
}

這是我用串口測(cè)試指令，發(fā)送格式要十六進(jìn)制發(fā)送
Q0.0 =1
發(fā)送：03 05 00 00 FF 00 8D D8
接受：03 05 00 00 FF 00 8D D8
Q0.0=0
發(fā)送：03 05 00 00 00 00 CC 28
接受：03 05 00 00 00 00 CC 28
Q0.1=1
發(fā)送：03 05 00 01 FF 00 DC 18
接受：03 05 00 01 FF 00 DC 18
Q0.2=1
發(fā)送：03 05 00 02 FF 00 2C 18
接受：03 05 00 02 FF 00 2C 18
Q0.3=1
發(fā)送：03 05 00 03 FF 00 7D D8
接受：03 05 00 03 FF 00 7D D8
Q0.4=1
發(fā)送：03 05 00 04 FF 00 CC 19
接受：03 05 00 04 FF 00 CC 19
Q0.5=1
發(fā)送：03 05 00 05 FF 00 9D D9
接受：03 05 00 05 FF 00 9D D9
Q0.6=1
發(fā)送：03 05 00 06 FF 00 6D D9
接受：03 05 00 06 FF 00 6D D9
Q0.7=1
發(fā)送：03 05 00 07 FF 00 3C 19
接受：03 05 00 07 FF 00 3C 19