Unit parameter in pymodbus custom request - pymodbus

Question

this is my firt post here.
I was lurking for a while.
So, I'm having problem regarding custom message in pymodbus ModbusTcpClient
I'm playing with one old Modbus device which has custom registers and commands.
I am able to read/write coils, registers, etc.
Problem is that this device needs special command for some sort of reset.
I made some wireshark sniffing and I made custom message, but I'm stuck in defining unit parameter.
here is code snippet:
class CustomModbusRequest(ModbusRequest):
function_code = 8
def __init__(self, address):
ModbusRequest.__init__(self)
self.address = address
self.count = 1
def encode(self):
return struct.pack('>HH', self.address, self.count)
def decode(self, data):
self.address, self.count = struct.unpack('>HH', data)
def execute(self, context):
if not (1 <= self.count <= 0x7d0):
return self.doException(ModbusExceptions.IllegalValue)
if not context.validate(self.function_code, self.address, self.count):
return self.doException(ModbusExceptions.IllegalAddress)
values = context.getValues(self.function_code, self.address,
self.count)
return CustomModbusResponse(values)
def custom_8():
client = ModbusTcpClient('192.168.0.222')
connection = client.connect()
request = CustomModbusRequest(170)
result = client.execute(request)
print(result)
time.sleep(1)
In normal request for read register there is specified unit parameter, like this:
request = client.read_input_registers(513,4, unit=0x4)
In custom request, I don't know how to specify this. In wireshark I can see that in custom message, I'm sending request to address 0, and I need to use address 4.
Please, help.

Answer 1

You will have to pass the unit to custom message and that should do the trick.
request = CustomModbusRequest(170, unit=<unit_id>). You also will have to update the __init__ of CustomModbusRequest to pass additional kwargs to parent.
class CustomModbusRequest(ModbusRequest):
function_code = 8
def __init__(self, address, **kwargs):
ModbusRequest.__init__(self, **kwargs)
self.address = address
self.count = 1
...
...
request = CustomModbusRequest(170, unit=<unit_id>)
result = client.execute(request)