function modbusReadHoldingRegister()

Read value from single holding register using modbus protocol. The call is asynchronous: the code execution proceeds immediately and when the response arrives, callback function is called.

nil modbusReadHoldingRegister(table config)

Parameters

table config{deviceAddress, callback, address,port, timeout}

• string deviceAddress IP address of device
• function{response} callback this function is called when response arrives
• string address number of the holding register
• optional number port numer of port (default 502)
• optional number timeout maximum seconds to wait for response (default 30)

Callback Parameters

table response{result, errInfo, address, value}

• number result error code of the response (0 is success)
• string errInfo error description (if result>0)
• number address number of the holding register
• string value value of the holding register

Return value

nil

Usage

-- Read value of all outputs from NETIO with IP 10.0.0.105 on port 505
function modbusReadCallback(data)
  if data.result == 0 then
    log(string.format("modbus addr %d, got %s", data.address, tostring(data.value)))
  else
    log(string.format("modbus coil addr %d failed with error %d: %s", data.address, data.result, data.errorInfo))
  end
end

for i = 101,104 do
  modbusReadHoldingRegister{deviceAddress='10.0.0.105', port=505, timeout=6, address=i, callback=modbusReadCallback}
end

Requirements

Netio FirmWare 3.3.0+