comModbusRtu.py

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# Copyright (c) 2012, Robotiq, Inc.
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# Modifed from the orginal comModbusTcp by Kelsey Hawkins @ Georgia Tech



"""@package docstring
Module comModbusRtu: defines a class which communicates with Robotiq Grippers using the Modbus RTU protocol. 

The module depends on pymodbus (http://code.google.com/p/pymodbus/) for the Modbus RTU client.
"""

from pymodbus.client.sync import ModbusSerialClient
from math import ceil

class communication:    

   def __init__(self):
      self.client = None
      
   def connectToDevice(self, device):
      """Connection to the client - the method takes the IP address (as a string, e.g. '192.168.1.11') as an argument."""
      self.client = ModbusSerialClient(method='rtu',port=device,stopbits=1, bytesize=8, baudrate=115200, timeout=0.2)
      if not self.client.connect():
          print "Unable to connect to %s" % device
          return False
      return True

   def disconnectFromDevice(self):
      """Close connection"""
      self.client.close()

   def sendCommand(self, data):   
      """Send a command to the Gripper - the method takes a list of uint8 as an argument. The meaning of each variable depends on the Gripper model (see support.robotiq.com for more details)"""
      #make sure data has an even number of elements   
      if(len(data) % 2 == 1):
         data.append(0)

      #Initiate message as an empty list
      message = []

      #Fill message by combining two bytes in one register
      for i in range(0, len(data)/2):
         message.append((data[2*i] << 8) + data[2*i+1])

      #To do!: Implement try/except 
      self.client.write_registers(0x03E8, message, unit=0x0009)

   def getStatus(self, numBytes):
      """Sends a request to read, wait for the response and returns the Gripper status. The method gets the number of bytes to read as an argument"""
      numRegs = int(ceil(numBytes/2.0))

      #To do!: Implement try/except 
      #Get status from the device
      response = self.client.read_holding_registers(0x07D0, numRegs, unit=0x0009)

      #Instantiate output as an empty list
      output = []

      #Fill the output with the bytes in the appropriate order
      for i in range(0, numRegs):
         output.append((response.getRegister(i) & 0xFF00) >> 8)
         output.append( response.getRegister(i) & 0x00FF)
      
      #Output the result
      return output