title: Read multiple holding register in pymodbus
body: <p>I'm using ModbusSerialClient of <a href="https://pymodbus.readthedocs.io/en/v1.3.2/examples/tk-frontend.html" rel="nofollow noreferrer">pymodbus</a> library. I've multiple registers that I want to read.</p>
  
  <p>I'm able to read one register at a time, but not able to figure out how to read all the registers at a single time for better performance.</p>
  
  <pre><code>registers = [3900,3902,3904,3906,3926,3860]
  client = ModbusSerialClient(method='rtu',port='/dev/ttyUSB0', timeout=1, parity='N', baudrate=19200, unit=1)
  client.connect()
  
  for register in registers:
      response = client.read_holding_registers(register, 2, unit=0x01)
  </code></pre>
  
  <p>I've tried something like this</p>
  
  <pre><code>add_min, add_max = min(registers), max(registers)
  no_bytes = add_max - add_min
  response = client.read_holding_registers(add_min, no_bytes, unit=0x01)
  </code></pre>
  
  <p>But it's throwing "Illegal Address" error.</p>