minimalmodbus校验和错误在rtu模式与2个设备

Question

我有一个带有USB CH340加密狗的RPI连接到EM340电能表。下面的代码可以很好地工作。

当我连接2个EM340电能表时，我得到以下错误:

pi@raspberrypi:~ $ python3 modbus_test.py
Traceback (most recent call last):
File "modbus_test.py", line 21, in <module>
freq2 = instrument.read_register(0x0033,1)  # Registernumber, number of decimals
File "/home/pi/.local/lib/python3.7/site-packages/minimalmodbus.py", line 486, in read_register
payloadformat=_Payloadformat.REGISTER,
File "/home/pi/.local/lib/python3.7/site-packages/minimalmodbus.py", line 1245, in _generic_command
payload_from_slave = self._perform_command(functioncode, payload_to_slave)
File "/home/pi/.local/lib/python3.7/site-packages/minimalmodbus.py", line 1330, in _perform_command
response, self.address, self.mode, functioncode
File "/home/pi/.local/lib/python3.7/site-packages/minimalmodbus.py", line 1867, in _extract_payload
raise InvalidResponseError(text)
minimalmodbus.InvalidResponseError: Checksum error in rtu mode: '6ý' instead of 'x99ò' . The response is: 'x01x01x00x00x166ý' (plain response: 'x01x01x00x00x166ý')

我代码:

import minimalmodbus
import serial
instrument = minimalmodbus.Instrument('/dev/ttyUSB0', 1)  # port name, slave address (in decimal)
#instrument.serial.port                     # this is the serial port name
instrument.serial.baudrate = 9600         # Baud
instrument.serial.bytesize = 8
#instrument.serial.parity   = serial.PARITY_NONE
instrument.serial.stopbits = 1
instrument.serial.timeout  = 0.2          # seconds
instrument.address = 1                         # this is the slave address number
#instrument.mode = minimalmodbus.MODE_ASCII   # rtu or ascii mode
instrument.mode = minimalmodbus.MODE_RTU
instrument.clear_buffers_before_each_transaction = True
instrument.close_port_after_each_call = True

## Read temperature (PV = ProcessValue) ##
freq2 = instrument.read_register(0x0033,1)  # Registernumber, number of decimals
txt = "Frekvens: {} Hz".format(freq2)
#0x0034
kwh_total  = instrument.read_register(0x0400)
kwh_total_2  = instrument.read_register(0x0402)
txt2 = "Total forbrug: {0}.{1} kWh".format(kwh_total,kwh_total_2)
w_l1 = instrument.read_register(0x0012,1)  # Registernumber, number of decimals
txt3 = "Nuværende forbrug: {} W".format(w_l1)
print(txt)
print(txt2)
print(txt3)

我已经根据https://web.evishine.dk/wp-content/uploads/2019/11/EM340-ENG.pdf第3页连接了2xEM340。

知道为什么我在rtu模式下得到校验和错误吗?

Answer 1

根据评论，如果你并行地连接两个具有相同ID的Modbus RTU设备，那么它们都将响应指向该Slave ID的任何请求。响应可能会发生冲突，这意味着您的代码将收到一个乱码响应(通过CRC检测)。

解决方法是修改其中一个设备的ID。