python - 如何使用 pymodbus 读取寄存器

Question

如何从 Register with pymodbus 中读取数据？

我正在尝试这段代码:

import pymodbus
from pymodbus.pdu import ModbusRequest
from pymodbus.client.sync import ModbusSerialClient as ModbusClient 
#initialize a serial RTU client instance
from pymodbus.transaction import ModbusRtuFramer

#count= the number of registers to read
#unit= the slave unit this request is targeting
#address= the starting address to read from

client = ModbusClient(method = 'rtu', port='/dev/extcomm/0/0', stopbits = 1, bytesize = 8, parity = 'N' , baudrate= 38400)

#Connect to the serial modbus server
 connection = client.connect()
 print(connection)

#Starting add, num of reg to read, slave unit.
coil  = client.read_holding_registers(0x01,1,unit=1)# address, count, 
slave address
print(coil)

#Closes the underlying socket connection
client.close()

这给了我这个错误:

    Modbus Error: [Input/Output] Modbus Error: [Invalid Message] Incomplete message received, expected at least 2 bytes (0 received)

我的slave id是1号，我要读的寄存器也是1号，但不知道为什么还是不行。

Answer 1

from pymodbus.client.sync import ModbusSerialClient as ModbusClient

client = ModbusClient(method='rtu', port='COM4', baudrate=2400, timeout=1)

client.connect()
read=client.read_holding_registers(address = 222 ,count =10,unit=1) 
//Address is register address e.g 30222, 
//and count is number of registers to read, 
//so it will read values of register 30222 to 30232
//unit is slave address, for 1 device leave it 1

data=read.registers[int(2)] #reading register 30223 
print(data) #printing value read in above line