CODEWITHSUNDEEP
rubymodbus-tcp
Twonky
Twonky

Reputation: 806

ModBus TCP communication using Ruby: failing to implement HelloWorld

I am able to communicate with a ventilation installation (Helios KWL EC 500 W which supports holding registers only, english description starts at 50% of the file) using the modpoll utility v3.4. But I failed to transfer the very first communication to Ruby and the rmodbus library v1.3.3.

With modpoll, I may request some temperature value with the command

./modpoll -m tcp -a 180 <ipaddr> 0x7630 0x3031 0x3034 0x0000

and then read the data using

./modpoll -m tcp -a 180 -t4:hex -c 8 -0 -1 <ipaddr>
 Protocol configuration: MODBUS/TCP
 Slave configuration...: address = 180, start reference = 1 (PDU), count = 8
 Communication.........: x.x.x.x, port 502, t/o 2.00 s, poll rate 1000 ms
 Data type.............: 16-bit register (hex), output (holding) register table
 -- Polling slave...
 [1]: 0x7630

which outputs 8 16bit registers as stated as example in the Helios modbus documentation. As very first step, I tried to move the read part to Ruby. However, my Ruby code times out:

require 'rmodbus'
ModBus::TCPClient.new(ipaddr, 502) do |client|
  client.with_slave(1) do |slave|
    slave.debug = true
    puts slave.holding_registers[180..187]
  end
end

and throws the exception

/var/lib/gems/2.3.0/gems/rmodbus-1.3.3/lib/rmodbus/slave.rb:241:in `rescue in query': 
Timed out during read attempt (ModBus::Errors::ModBusTimeout)
from /var/lib/gems/2.3.0/gems/rmodbus-1.3.3/lib/rmodbus/slave.rb:232:in `query'
from /var/lib/gems/2.3.0/gems/rmodbus-1.3.3/lib/rmodbus/slave.rb:164:in `read_holding_registers'

What's wrong?

I am not sure if / how to use the parameters output by modpoll "address =180" and "start reference =1". Is "address" equivalent to "holding register #"?

Upvotes: 4

Views: 732

Answers (1)

Twonky
Twonky

Reputation: 806

Okay, this one was rather stupid. For the records (and others who might want to talk to their Helios using rmodbus):

slave.debug = 1

turns on the debugging which outputs the byte stream sent to the modbus slave. The first bytes sequence is supposed to be: transaction number (2 byte), protocol specifier (2 byte, always zero), size of the following message (2 byte), unit identifier (1 byte, always 180 for Helios KWL).

The slave needs to be initialized with its unit identifier 180, instead of 1:

client.with_slave(180) do |slave|

Upvotes: 2

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