Empty answer

[MGGEL]

I'am trying to read some registers from a slave. But the response seems to be empty without any error.

Here is the code:

from pymodbus.client import ModbusTcpClient
from pymodbus.payload import BinaryPayloadDecoder
from pymodbus.constants import Endian

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

client = ModbusTcpClient('192.168.188.30')

client.connect()

result = client.read_holding_registers(40028,2,1)


print(result.function_code)
print(result.bits)
decoder = BinaryPayloadDecoder.fromRegisters(result.registers)#,byteorder=Endian.Little,wordorder=Endian.Big)
print(decoder.decode_bits())
client.close()

And this is the debugging output:

DEBUG:pymodbus.logging:Connection to Modbus server established. Socket ('192.168.188.129', 62263)
DEBUG:pymodbus.logging:Current transaction state - IDLE
DEBUG:pymodbus.logging:Running transaction 1
DEBUG:pymodbus.logging:SEND: 0x0 0x1 0x0 0x0 0x0 0x6 0x1 0x3 0x9c 0x5c 0x0 0x2
DEBUG:pymodbus.logging:New Transaction state "SENDING"
DEBUG:pymodbus.logging:Changing transaction state from "SENDING" to "WAITING FOR REPLY"
DEBUG:pymodbus.logging:Changing transaction state from "WAITING FOR REPLY" to "PROCESSING REPLY"
DEBUG:pymodbus.logging:RECV: 0x0 0x1 0x0 0x0 0x0 0x3 0x1 0x83 0xb
DEBUG:pymodbus.logging:Processing: 0x0 0x1 0x0 0x0 0x0 0x3 0x1 0x83 0xb
DEBUG:pymodbus.logging:Factory Response[131]
DEBUG:pymodbus.logging:Adding transaction 1
DEBUG:pymodbus.logging:Getting transaction 1
DEBUG:pymodbus.logging:Changing transaction state from "PROCESSING REPLY" to "TRANSACTION_COMPLETE"
131
[]
DEBUG:pymodbus.logging:[]
[]

Could someone tell me, what am i doing wrong?

[janiversen]

read_holding_register do not return bits but registers.

[janiversen]

read_coils return bits.

It´s all in the documentation.

[janiversen]

btw your call to decoder is not really needed for neither coils nor registers, unless you want to do some special things. The library automatically convert a register to your CPU specification.