writing negative value with client.write_register

[Khalil Tabbal]

Hi everyone,

I have implemented a sync client to write to register

I have a problem using this code

   

client.open()
rq = client.write_register(52000, -10, unit=0x01)
print rq
client.close()

I get the following error :

return struct.pack('>HH', self.address, self.value)

error: integer out of range for 'H' format code

Is there another way to write negative integers ton a register ?

Best regards,

[Galen Collins]

Khalil,

Take a look at the payload builder which is useful for shoving various types into the modbus registers.  Here is an example you can work with:

http://pymodbus.readthedocs.org/en/latest/examples/modbus-payload.html

Depending on the size of your negative value, use the builder.add_8bit_int (or 16, 32, 64).

Galen

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[Khalil Tabbal]

Galen,

Thank you for your quick answer, I have a look at the payload builder, I need to write 16 bit signed

my values are -360 < x < 360 

[Khalil Tabbal]

Hello,

I am setting a target_power which is an integer -360 < target_power < 360

My working code is the following but I can only send target_power >= 0 

# -*- coding: utf-8 -*-

import sys
import logging
from pymodbus.client.sync import ModbusTcpClient as ModbusClient

target_power = 10

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


client = ModbusClient('192.168.1.100', port=502) # client
client.connect() # open the client
result = client.write_register(52000, 10, unit=0x01)
print result
client.close() # close the client

DEBUG:pymodbus.transaction:0x0 0x1 0x0 0x0 0x0 0x6 0x1 0x6 0x20 0xcb 0xa 0x0

With payload : 

# -*- coding: utf-8 -*-

import sys
import logging
from pymodbus.constants import Endian
from pymodbus.payload import BinaryPayloadDecoder
from pymodbus.payload import BinaryPayloadBuilder
from pymodbus.client.sync import ModbusTcpClient as ModbusClient

target_power = 10

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


client = ModbusClient('192.168.1.100', port=502) # client
client.connect() # open the client


# Modbus payload building
builder = BinaryPayloadBuilder(endian=Endian.Little)
builder.add_16bit_int(target_power)
payload = builder.build()


result = client.write_registers(52000, payload, unit=0x01, skip_encode=True) # Ecriture des donnees
print result
client.close() # close the client

I get the following debug : DEBUG:pymodbus.transaction:0x0 0x1 0x0 0x0 0x0 0x6 0x1 0x10 0x21 0xcb 0x1 0x0

Best regards,