when i got the exception:ModbusInvalidResponseError, "Invalid CRC in response" , it can't execute about modbus-tk HOT 12 CLOSED

Hello

I am not sure that I understand your problem.

Do you miss a modbus_tk.modbus_rtu.ModbusInvalidResponseError exception when the
slave returns an bad CRC?

Is it right?

I have set the timeout 3.0s, and catched it.
my code like this:

>>modbus code:

    master = modbus_rtu.RtuMaster(serial)
    master.set_timeout(3.0)
    master.set_verbose(True)
    while True:
            try:
                resp = self.master.execute(1, cst.READ_HOLDING_REGISTERS, 13, 1)
            except modbus_tk.modbus.ModbusError, e:
                logger.error("%s- Code=%d" % (e, e.get_exception_code()))
            except modbus_tk.modbus_rtu.ModbusInvalidResponseError, e:
                logger.error("%s- Code=ModbusInvalidResponseError" % (e))
                self.master.close()
            except:
                logger.debug("other")

additional, i have run that code in a thread like this:
self.thread = threading.Thread(target=self.Run, args=(self.dct, self.dctname))
self.thread.setDaemon(1)
self.thread.start()
self.alive.set()

def Run(self, dct, dctname):
    while self.alive.isSet():
        master....

i find a method to resolve this problem:
when catch this type of exception:
i try to do master.close(),
then it can work normaly

So the problem was that you were not able to communicate anymore after a bad CRC
query. Right?

Normaly, the master should "flush" the buffer before sending a query so you 
shouldn't
have this problem. I 'll look at this pb.

However if you have a workaround that fix the pb, it's perfect.

Best 

when modbus_tk.modbus_rtu.ModbusInvalidResponseError exception raised, i try to 
use
master.close() to fix it.
unfortunately , it raised a new Exception like this:
Response length is invalid 0- Code=ModbusInvalidResponseError.
although I tried to use master.close() to make it work, it also return "Response
length is invalid 0- Code=ModbusInvalidResponseError" on the next loop every 
time.

this is my log:

2010-05-11 15:22:16,407 ERROR   main.Run    Thread-1    Invalid CRC in response-
Code=ModbusInvalidResponseError
2010-05-11 15:22:16,407 DEBUG   modbus.execute  Thread-1    -> 1-3-0-13-0-1-21-201
2010-05-11 15:22:18,421 DEBUG   modbus.execute  Thread-1    <-
2010-05-11 15:22:18,421 ERROR   main.Run    Thread-1    Response length is invalid 0-
Code=ModbusInvalidResponseError
2010-05-11 15:22:18,421 DEBUG   modbus.execute  Thread-1    -> 1-3-0-15-0-1-180-9
2010-05-11 15:22:20,436 DEBUG   modbus.execute  Thread-1    <-
2010-05-11 15:22:20,436 ERROR   main.Run    Thread-1    Response length is invalid 0-
Code=ModbusInvalidResponseError
2010-05-11 15:22:20,436 DEBUG   modbus.execute  Thread-1    -> 1-3-0-16-0-41-133-209

It seems that you don't receive any answer at all. Maybe you should investigate 
why
the device doesn't answer. Maybe teh query is not Oh (wrong slave id?)

Have you set a timeout? master.set_timeout(1.0) set a 1 sec timeout. If no 
answer is
received before the to elapsed an exception should be raised. Maybe the 
Exception
name should be improved.

But getting an exception is not a problem, you should catch it.

Hi Luc,

I have found another pb,

>>code:
    logger.info(master.execute(4, cst.READ_HOLDING_REGISTERS, 16, 
    expected_length = 38))

when the expected_length=38 it raise a exception like this:
   "modbus_tk.modbus.ModbusInvalidResponseError: Response address 3 is different from
request address 4 "

when the expected_length>=39 it raise a exception like this:
    "modbus_tk.modbus.ModbusInvalidResponseError: Invalid CRC in response"

i think may be my device has some problem

i use another tool to test my device , it work nice.
i think there are some thing wrong in pyserial.
when it read the serial port ,it can't read the whole respose byte.
so i got a bad CRC

Have you tried to remove the expected length? it should calculate the right 
length
for you

Please try the expected_length and rev 110 where reopen of the port has been 
slightly
improved