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在modbustcp reading中第二次尝试获得结果的原因是什么?

pymodbus modbus python

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Benyamin Jafari · 技术社区 · 6 年前

有时,当我第一次从modbus设备读取数据时,会立即得到错误响应,但当我再次尝试时,这个响应是预期的结果。

这是第一次出现的错误消息:

pymodbus.exceptions.ModbusIOException(pymodbus.exceptions.InvalidMessageReceivedException('Incomplete message received, expected at least 8 bytes (0 received)'), 3)

以下是ipython控制台中的简化代码片段:

In [1]: from pymodbus.client.sync import ModbusTcpClient
In [2]: cli = ModbusTcpClient('192.168.1.152', port=502)
In [3]: cli.connect()
Out[3]: True
In [4]: req = cli.read_holding_registers(0x1e, 2, unit=21)  # First try.
In [5]: req.isError()
Out[5]: True
In [6]: req
Out[6]: pymodbus.exceptions.ModbusIOException(pymodbus.exceptions.InvalidMessageReceivedException('Incomplete message received, expected at least 8 bytes (0 received)'), 3)
In [7]: req = cli.read_holding_registers(0x1e, 2, unit=21)  # Second try.
In [8]: req.isError()
Out[8]: False
In [9]: req.registers  # As expected.
Out[9]: [16091, 15697]

原因是什么?

[更新]:

我激活modbus从机/服务器日志:

import logging
from pymodbus.client.sync import ModbusTcpClient as ModbusClient

logging.basicConfig()
log = logging.getLogger()
log.setLevel(logging.DEBUG)

client = ModbusClient('192.168.1.152', port=502)
client.connect() 

print('First Try: ')
res = client.read_holding_registers(0x1e, 2, unit=21)
print('isError = {}'.format(res.isError()))

print('Second Try: ')
res = client.read_holding_registers(0x1e, 2, unit=21)
print('isError = {}'.format(res.isError()))

client.close()

出:

First Try: 
DEBUG:pymodbus.transaction:Current transaction state - IDLE
DEBUG:pymodbus.transaction:Running transaction 1
DEBUG:pymodbus.transaction:SEND: 0x0 0x1 0x0 0x0 0x0 0x6 0x15 0x3 0x0 0x1e 0x0 0x2
DEBUG:pymodbus.client.sync:New Transaction state 'SENDING'
DEBUG:pymodbus.transaction:Changing transaction state from 'SENDING' to 'WAITING FOR REPLY'
DEBUG:pymodbus.transaction:Transaction failed. (Modbus Error: [Invalid Message] Incomplete message received, expected at least 8 bytes (0 received)) 
DEBUG:pymodbus.framer.socket_framer:Processing: 
DEBUG:pymodbus.transaction:Getting transaction 1
DEBUG:pymodbus.transaction:Changing transaction state from 'PROCESSING REPLY' to 'TRANSACTION_COMPLETE'
isError = True
Second Try: 
DEBUG:pymodbus.transaction:Current transaction state - TRANSACTION_COMPLETE
DEBUG:pymodbus.transaction:Running transaction 2
DEBUG:pymodbus.transaction:SEND: 0x0 0x2 0x0 0x0 0x0 0x6 0x15 0x3 0x0 0x1e 0x0 0x2
DEBUG:pymodbus.client.sync:New Transaction state 'SENDING'
DEBUG:pymodbus.transaction:Changing transaction state from 'SENDING' to 'WAITING FOR REPLY'
DEBUG:pymodbus.transaction:Changing transaction state from 'WAITING FOR REPLY' to 'PROCESSING REPLY'
DEBUG:pymodbus.transaction:RECV: 0x0 0x2 0x0 0x0 0x0 0x7 0x15 0x3 0x4 0x3f 0x99 0x8 0xe8
DEBUG:pymodbus.framer.socket_framer:Processing: 0x0 0x2 0x0 0x0 0x0 0x7 0x15 0x3 0x4 0x3f 0x99 0x8 0xe8
DEBUG:pymodbus.factory:Factory Response[ReadHoldingRegistersResponse: 3]
DEBUG:pymodbus.transaction:Adding transaction 2
DEBUG:pymodbus.transaction:Getting transaction 2
DEBUG:pymodbus.transaction:Changing transaction state from 'PROCESSING REPLY' to 'TRANSACTION_COMPLETE'
isError = False

如你所见,在第一次尝试中我得到了一个错误,但在第二次尝试中我得到了一个好的结果。

1 回复 | 直到 6 年前

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RDorsch 6 年前

我对Keba热泵控制器也有同样的问题。正如其他人提到的,我的问题是通过将超时时间增加到10秒来解决的,在您的示例中

client=modbusclient('192.168.1.152',端口=502,超时=10)

10秒对我来说有一定的差距,我在wireshark中观察到的时间总是在5秒左右。从第二个请求开始,响应总是很容易在几秒钟内到达。

我的热泵供应商给出的原因是控制器内存不足,而modbus服务器只在第一次收到连接请求时启动。

@pymodbus开发人员:我建议将default.timeout增加到10秒。