raspi python rs485

import serial, time

message_start = "/?%s!\r\n"
message_login = "\x01P1\x02(00000000)\x03"
message_read  = "\x01R1\x02%s()\x03"
message_exit  = "\x01B0\x03"
message_mode  = "\x060:1\r\n"

meter_list = ['001511420141','001511420142','001511420143']
address_list = ['00000000', '00000003','00000004','00000010','00000036']
error_list = [0,0,0]

state_disconnected=10
state_wait_identification=11
state_wait_password_prompt=12
state_wait_password_verification=13
state_wait_data_read=14
state_data_available=15

state = state_disconnected
wait_response = 1
current_index = 0
current_meter = 0

#ser = serial.Serial('/dev/pts/0', 115200, timeout=3)
ser = serial.Serial('/dev/ttyUSB1', 9600, timeout=0.1, bytesize=serial.SEVENBITS, parity=serial.PARITY_EVEN)

def addBCC(data):
   b = 0
   for ch in data[1:]:
      b ^= ord(ch)
   data = data + chr(b)
   return data

def sendMessage(message, param=None, bcc=0):
   if param:
      message = message % param
      if bcc:
         message = addBCC(message)
      ser.write(message)
   else:
      message = message.replace("%s","")
      if bcc:
         message = addBCC(message)
      ser.write(message)

def sendExit():
   global state, meter_index, error_list
   sendMessage(message_exit, bcc=1)
   state = state_disconnected
   error_list[meter_index] += 1

def disconnect():
   global state, meter_index, error_list
   sendMessage(message_exit, bcc=1)
   state = state_disconnected
   print "logout"

def handle_wait_identification(data):
   global state, wait_response
   if data.startswith('/YTL'):
      print "ok. sending mode ..."
      sendMessage(message_mode)
      wait_response = 1
      state = state_wait_password_prompt
   else:
      sendExit()
      state = state_disconnected
      print "error"

def handle_wait_password_prompt(data):
   global state, wait_response
   print data
   print ord(data[0])
   print ord(data[1])
   print ord(data[2])
   print ord(data[3])
   if ord(data[0])==1 and ord(data[1])==80 and ord(data[2])==48:
   #if data.startswith('p0'):
      print "ok. sending password ..."
      sendMessage(message_login, None, 1)
      state = state_wait_password_verification
      wait_response = 1
   else:
      sendExit()
      state = state_disconnected
      print "error handle_wait_password"

def send_data_request():
   global state, wait_response, current_index
   addr = address_list[current_index]
   print "sending data request ... %s" % (addr)
   sendMessage(message_read, addr, 1)
   state = state_wait_data_read
   wait_response = 1

def handle_wait_password_verification(data):
   global state, wait_response
   if data.startswith('\x06'):
   #if data.startswith('a'):
      print "password ok"
      send_data_request()
   else:
      sendExit()
      state = state_disconnected
      print "error"

def handle_wait_data_read(data):
   global state, wait_response, current_index
   print data
   current_index += 1
   if current_index < len(address_list):
      send_data_request()
   else:
      disconnect()
      state = state_disconnected
      print "done"


def read_meter_data(index):
   global state, wait_response, current_index, meter_index
   meter_index = index
   time.sleep(0.1)
   current_index = 0
   meter_id = meter_list[meter_index]
   print "start reading meter ... %s" % meter_id
   sendMessage(message_start, meter_id)
   state = state_wait_identification
   wait_response = 1
   while wait_response:
      wait_response = 0
      ser.flushInput()
      time.sleep(0.2)
      data = ser.read(64)
      if data and len(data) > 0:
         print "received bytes: %d" % len(data)
         if state == state_wait_identification:
            handle_wait_identification(data)
            continue
         if state == state_wait_password_prompt:
            handle_wait_password_prompt(data)
            continue
         if state == state_wait_password_verification:
            handle_wait_password_verification(data)
            continue
         if state == state_wait_data_read:
            handle_wait_data_read(data)
            continue
      else:
         print "fail"
         sendExit()
         state = state_disconnected

max_steps = 1000
for i in range(max_steps):
   print "loop %d of %d ..." % (i, max_steps)
   for meter in range(len(meter_list)):
      read_meter_data(meter)
   for meter in range(len(meter_list)):
      print "Errors for meter[%s]: %d" %  (meter_list[meter], error_list[meter])

ser.close()