from pymodbus.server import StartTcpServer from pymodbus.device import ModbusDeviceIdentification from pymodbus.datastore import ModbusSlaveContext, ModbusServerContext from pymodbus.datastore import ModbusSequentialDataBlock Default size: 0x00 to 0xFF (256 addresses each) store = ModbusSlaveContext( di=ModbusSequentialDataBlock(0, [0] * 100), # Discrete Inputs (read-only) co=ModbusSequentialDataBlock(0, [0] * 100), # Coils (read-write) hr=ModbusSequentialDataBlock(0, [0] * 100), # Holding Registers (read-write) ir=ModbusSequentialDataBlock(0, [0] * 100) # Input Registers (read-only) ) Set initial test values (example) store.setValues(3, 0, [123, 456, 789]) # Holding register addresses 0,1,2 = 123,456,789 Wrap in server context (slave ID 1) context = ModbusServerContext(slaves=store, single=True) Device identification (optional) identity = ModbusDeviceIdentification() identity.VendorName = 'Modbus Slave Example' identity.ProductCode = 'PYM' identity.VendorUrl = 'https://github.com/pymodbus-dev/pymodbus' identity.ProductName = 'PyModbus Slave' identity.ModelName = 'PyModbus Slave' identity.MajorMinorRevision = '1.0' Start TCP Modbus server on port 5020 (requires admin for 502) print("Modbus Slave running on port 5020...") StartTcpServer(context=context, identity=identity, address=("0.0.0.0", 5020))
Here’s a key piece of code in Python using the pymodbus library. This creates a slave (server) that holds simulated register data and responds to Modbus requests. modbus slave key