Question

我使用Python 2.7.5向modbus tcp模拟器发送消息。我不明白为什么python在sendall上发送两次最后一个字节：

这是python脚本根据我的代码（下面）打印出来的......

S: 00020000000c1110000400030600790083008d
R: 000200000006111000040003
R: 8d0000000003d8f603

模拟器将此记录在哪里（从脚本接收TX并将RX发送到脚本）...

TX: 00020000000c1110000400030600790083008d
RX: 000200000006111000040003
TX: 8d
Modbus message in error x03
RX: 8d0000000003d8f603

所以问题是......为什么8d发送两次（根据modbus模拟器监听）？模拟器因为它而抛出错误...... 代码摘录：

def writeMultipleHoldingRegister(socket, transactionid, unitid, address,valuesToWrite):
    TRANSACT_ID_BYTES = convertIntToBytes(int(transactionid))
    DATA_ADDRESS_BYTES = convertIntToBytes(int(address))
    FUNCTIONCODE_BYTES = '10'
    NUMREGISTERS_BYTES = convertIntToBytes(len(valuesToWrite))
    NUMBYTES = len(valuesToWrite)*2
    NUMBYTES_BYTES = str(('%04X' % NUMBYTES)[2:4])
    MESSAGE_LENGTH_BYTES = convertIntToBytes(int(6+(len(valuesToWrite)*2)))
    modbustcp_write = (TRANSACT_ID_BYTES + '0000' + MESSAGE_LENGTH_BYTES + unitid + FUNCTIONCODE_BYTES + DATA_ADDRESS_BYTES + NUMREGISTERS_BYTES + NUMBYTES_BYTES).decode('hex')
    for value in valuesToWrite:
        modbustcp_write = modbustcp_write + convertIntToBytes(int(value)).decode('hex')
    print 'S:', binascii.hexlify(modbustcp_write)
    socket.sendall(modbustcp_write) #modbus tcp
    data = socket.recv(12)
    print 'R:', binascii.hexlify(data)

    HOST = 'localhost'
    PORT = 502
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    s.connect((HOST, PORT))
    writeMultipleHoldingRegister(s, 2, '11', 4, [121, 131, 141])
    print 'R:', binascii.hexlify(s.recv(100))
    s.close()

评论中留下了以下建议。 Process Monitor向我显示了流量，但没有显示字节本身。所以我下载并运行了RawCAP并在Wireshark中查看了输出。用来解释......在哪里＆＃39; S＆＃39;是由模拟器发送的＆＃39; R＆＃39;是模拟器收到的......

R: 00020000000c1110000400030600790083008d (modbus request recv)
S: 000200000006111000040003 (modbus ack good request sent)
S: 8d0000000003d8f603 (modbus error notification sent...wtf)

我从未见过＆＃39; 8d＆＃39;收到两次......所以我不知道这里发生了什么。也许是模拟器中的一个错误... http://www.plcsimulator.org/

为什么python sendall发送两次最后一个字节？

0 个答案: