Re: [Minimalmodbus-list] Error with MinimalModbus

[Jonas B. <jon...@ho...>]

Hi Paddy,
and sorry for the delay in my response.

To change the baudrate, you should use:
instrument.serial.baudrate = 9600
It is described in more detail on
http://minimalmodbus.sourceforge.net/index.html#default-values

To see all the settings, you can use:
print(instrument)

Your code should look something like:

#!/usr/bin/env python
import minimalmodbus
minimalmodbus.CLOSE_PORT_AFTER_EACH_CALL = True

instrument = minimalmodbus.Instrument('com3', 1) # port name, slave
address (in decimal)
instrument.debug = True
instrument.serial.baudrate = 9600
print(instrument)

print( instrument.read_register(2822, numberOfDecimals=1,
functioncode=3))

The output produced by MinimalModbus seems to be correct:

'\x01\x03\x0b\x06\x00\x01f/'

Displayed Hex   Dec Description
\x01      01    1   Slave address (here 1)
\x03      03    3    Function code (here 3 = read registers)
\x0b      0b    11  Start address MSB
\x06      06    6   Start address LSB
\x00      00    0   Number of registers MSB
\x01      01    1   Number of registers LSB
f         66    106 CRC LSB
/         2F    47  CRC MSB

The register address is 11*256 + 6 = 2822

The CRC seems to be correct:
>>> minimalmodbus._calculateCrcString('\x01\x03\x0b\x06\x00\x01')
'f/'

Please paste the output from the code above in an e-mail, and I will
help you solve the problem.
Best regards
Jonas


<-----Ursprungligt Meddelande----->

 	 	From: Paddy Finn [pad...@gm...]
Sent: 3/12/2012 6:06:09 PM
To: min...@li...
Subject: [Minimalmodbus-list] Error with MinimalModbus 

Hiya,

I am trying to use MinimalModbus with Python33 on a Windows 64-bit
system. The USB->RS485 device is a PL2303 which sets up a virtual COM
port on COM3. The modbus device I'm reading is an energy meter with a
baud rate of 9600, byte size of 8 bits, no parity, and 1 stop bit. I
know that it is correctly set up as I can use some ModBus polling
software querying COM3 with the aforementioned settings. 


	I am using the following python code to attempt to read the
device using MinimalModbus:
	#!/usr/bin/env python
	import minimalmodbus
	minimalmodbus.CLOSE_PORT_AFTER_EACH_CALL = True
	print(minimalmodbus._getDiagnosticString())
	print(minimalmodbus.BAUDRATE)
	
	
	instrument = minimalmodbus.Instrument('com3', 1) # port name,
slave address (in decimal)
	instrument.debug = True
	instrument.CLOSE_PORT_AFTER_EACH_CALL = True
	instrument.BAUDRATE = 9600
	instrument.BYTESIZE = 8
	instrument.STOPBITS = 1
	print(instrument.BAUDRATE)
	print( instrument.read_register(2822, numberOfDecimals=1,
functioncode=3))


But unfortunately it is returning the following:

	19200
	9600
	MinimalModbus debug mode. Writing to instrument:
'\x01\x03\x0b\x06\x00\x01f/'
	MinimalModbus debug mode. Response from instrument: ''
	Traceback (most recent call last):
	  File "C:/Python33/Register Python.py", line 16, in <module>
	    print( instrument.read_register(2822, numberOfDecimals=1,
functioncode=3))
	  File "C:\Python33\lib\site-packages\minimalmodbus.py", line
174, in read_register
	    return self._genericCommand(functioncode, registeraddress,
numberOfDecimals=numberOfDecimals)
	  File "C:\Python33\lib\site-packages\minimalmodbus.py", line
261, in _genericCommand
	    payloadFromSlave = self._performCommand(functioncode,
payloadToSlave)
	  File "C:\Python33\lib\site-packages\minimalmodbus.py", line
317, in _performCommand
	    response            = self._communicate(message)
	  File "C:\Python33\lib\site-packages\minimalmodbus.py", line
395, in _communicate
	    raise IOError('No communication with the instrument (no
answer)')
	OSError: No communication with the instrument (no answer)


I have no idea where to start to find the problem and I was hoping that
you could perhaps shed some light on what it is that I am doing wrong.

Thanks a million!!

Paddy


<P><p><font face="Arial, Helvetica, sans-serif" size="2" style="font-size:13.5px">_______________________________________________________________<BR>Annons: <a href="http://adserver.adtech.de/?adlink|3.0|1297|4132301|1|16|AdId=8371245;BnId=1;link=http://www.vistaprint.se/vp/gateway.aspx?S=7280236673" target="_blank">Grattis! Nu kan du få en unik väggkalender gratis! Ladda upp dina favoritfoton och gör varje månad minnesvärd! Beställ nu och få en fotomugg på köpet!</a></font>