How do I fix a PyModbus Unable to decode Response-Error with IF96015 Interface by IME

Question

I have a PyModbus running on a Raspberry PI 3b. I have the IF96015 Ethernet Interface for the Nemo 96HD Digital Multimeter. When I try to connect to it over ModbusTCP with the PyModbus console I can ask if it is connected and it says "true" but I cannot read any data from it.

According to the manuals the first used address is 301 and when I try to read the .Coil() I get:

"original_function_code": "1 (0x1)", 
"error": "[Input/Output] No Response received from the remote unit/Unable to decode response"

Open the Console:

pymodbus.console tcp --host 192.168.178.200 --port 502

Check for connection:

client.connect

Try to read a Coil:

client.read_coils address 301 count 1

Output:

"original_function_code": "1 (0x1)", 
"error": "[Input/Output] Modbus Error: [Invalid Message] Incomplete message received, expected at least 8 bytes (0 received)"

[NOTE]:

Manuals of the IF96015:

Manual_1

Manual_2

Which code do you mean? Because it is running in the pymodbus Console. — DJCheeky, Oct 20 '18 at 20:18
I have a Example Code rom pymodbus.client.sync import ModbusTcpClient client = ModbusTcpClient('192.168.178.200') result = client.read_coils(0x301) print(result) client.close() This will give me an Output of: Modbus Error: [Input/Output] Modbus Error: [Invalid Message] Incomplete message received, expected at least 8 bytes (0 received) — DJCheeky, Oct 20 '18 at 20:20
Please put your full code in your question for better express shown. I think you need to `unit` argument and using `result.registers` instead of result, So I suggest to you put on your code for better interaction — Benyamin Jafari, Oct 20 '18 at 20:30
When you install pyModBus you can type pymodbus.console to get A Console prompt — DJCheeky, Oct 20 '18 at 20:53
I dont have much more code than that because I use the console to try everything out — DJCheeky, Oct 20 '18 at 20:55
So can you put on your commands that you have on pymodbus.console on your question (On your question, not in this place (comment section))?! — Benyamin Jafari, Oct 20 '18 at 20:59
Did you try `unit` argument in `read_coil()` method? check this [link](https://stackoverflow.com/a/52791339/3702377) for more information. — Benyamin Jafari, Oct 20 '18 at 21:02
I didn't know about this tool, thanks +1, I will post an answer for this question — Benyamin Jafari, Oct 21 '18 at 05:48

Benyamin Jafari · Answer 1 · 2018-10-21T06:37:08.930

1

Each Modbus slave/server has a unit_ID, so you need to add this on .read_coil() method.

In many cases unit argument is equal to 1 as default in Modbus slave side.

Here is an example (Modbus client):

pymodbus.console tcp --host 192.168.178.200 --port 502
client.connect
client.read_coils address=301 count=1 unit=1

Here is another example with multiple reading with .read_holding_registers() and its decoder:

client.read_holding_registers count=4 address=9 unit=1
{
    "registers": [
        60497,
        47134,
        34091,
        15424
    ]
}


result.raw
{
    "registers": [
        15626,
        55203,
        28733,
        18368
    ]
}

result.decode word_order=little byte_order=little formatters=float64
28.17

[NOTE]:

read_coil() read/write digital values (1 bit)
read_holding_registers() read/write analog values (16 bits)
Some address are hexadecimal (maybe 0x301 instead 301)
Don't forget = after each argument like this (count=1 instead of count 1)

edited Oct 21 '18 at 06:37

answered Oct 21 '18 at 06:13

Benyamin Jafari

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Could you determiniert in the Manual 2 wheiter 301 is a Register or a coil? – DJCheeky Oct 21 '18 at 09:40
When I try client.read_holding_registers I get this > client.read_holding_registers address=301 count=1 unit=1 { "original_function_code": "3 (0x3)", "error": "[Input/Output] Modbus Error: [Invalid Message] Incomplete message received, expected at least 8 bytes (0 received)" } > – DJCheeky Oct 21 '18 at 09:52
And with 0x301 I get: > client.read_holding_registers address=0x301 count=1 unit=1 ValueError("invalid literal for int() with base 10: '0x301'",) – DJCheeky Oct 21 '18 at 09:53
It is the same as with the registers – DJCheeky Oct 21 '18 at 10:15
Is your example with the Multiple Registers for this Device? – DJCheeky Oct 21 '18 at 10:16
So your problem may be in the address, I'll read the manual_2 – Benyamin Jafari Oct 21 '18 at 10:20
No, I tested it with a Delta_PLC and Delta_gateway, that these are Modbus TCP, but I know about that registers address and read count and unit_ID – Benyamin Jafari Oct 21 '18 at 10:21
Ah ok so I should be a Address mistake? – DJCheeky Oct 21 '18 at 11:45
I think it maybe yes. – Benyamin Jafari Oct 21 '18 at 11:50
I have tried > client.read_device_information { "original_function_code": "43 (0x2b)", "error": "[Input/Output] No Response received from the remote unit/Unable to decode response" } > so there is no address wich could be wrong but I get the error to – DJCheeky Oct 21 '18 at 12:20
try with the `--verbose` option and share the logs. – Sanju Oct 24 '18 at 03:40
It could be that you are using the wrong address, the offset is in hex and the console takes the values as plain int , so you will have to explicitly convert the hex to int and use the offset (`0x301 == 769`) – Sanju Oct 24 '18 at 03:45
@DJCheeky check the "Sanju" comments. – Benyamin Jafari Oct 24 '18 at 05:07

score 1 · Answer 2 · edited Jan 27 '19 at 19:49

1

In Manual 2, the address is 0x301 hex. Try client.read_coils address = 769 count = 1. Addresses should be given in decimal format (hex 0x301 = dec 769).

edited Jan 27 '19 at 19:49

JoSSte

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answered Jan 27 '19 at 18:07

Mirek

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1

score 0 · Accepted Answer · answered Apr 25 '19 at 07:07

I have found a solution to this. The problem is in the default value for the unit ID. The manual which can be found at the vendor's website shows an example Modbus TCP packet format with unit ID value set to "1".

But the factory setting for unit ID is "255". You can change the default address in a menu, password 3002. Now, I can read values with the following Python code:

message = tcp.read_holding_registers(slave_id=255, starting_address=0x1000, quantity=6)
response = tcp.send_message(message, sock)

How do I fix a PyModbus Unable to decode Response-Error with IF96015 Interface by IME

3 Answers3