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1. Install modpoll onto your system, which you are using to connect to the Modbus RTU device via a serial interface

2. We will now have to check the manual of the W2SC to see, what kind of register structure the device has

   Register	Type	Value
   2000	Slave ID	42
   2001	Modbus mode	1 = ASCI 2 = RTU
   2002	Parity	1 = None 2 = Odd 3 = Even (default)
   2003	Baud rate	default 9600 Baud
   2005	Command register	0x42 = write configuration to EEPROM 0x24 = reset the device

3. As in the documentation described, changing the parity requires the using the register 2002

4. First we read from the device using the following command

   Code Block

   root@ubuntu:/# modpoll -a 42 -b 9600 -d 8 -p even -s 1 -t 4 -0 -r 2002 -c 1 /dev/ttyUSB0 modpoll 3.4 - FieldTalk(tm) Modbus(R) Master Simulator Copyright (c) 2002-2013 proconX Pty Ltd Visit http://www.modbusdriver.com for Modbus libraries and tools. Protocol configuration: Modbus RTU Slave configuration...: address = 42, start reference = 2002 (PDU), count = 1 Communication.........: /dev/ttyUSB0, 9600, 8, 1, even, t/o 1.00 s, poll rate 1000 ms Data type.............: 16-bit register, output (holding) register table -- Polling slave... (Ctrl-C to stop) [2002]: 3

5. The device is thus correctly set in parity even, now we will change it to parity none, by adding a 1 to the command line used previously

   Code Block
   root@ubuntu:/# modpoll -a 42 -b 9600 -d 8 -p even -s 1 -t 4 -0 -r 2002 -c 1 /dev/ttyUSB0 1 . . . Protocol configuration: Modbus RTU Slave configuration...: address = 42, start reference = 2002 (PDU), count = 1 Communication.........: /dev/ttyUSB0, 9600, 8, 1, even, t/o 1.00 s, poll rate 1000 ms Data type.............: 16-bit register, output (holding) register table Written 1 reference.

6. To write the changes to the device, we need to use the register 2005

   Code Block
   root@ubuntu:/# modpoll -a 42 -b 9600 -d 8 -p even -s 1 -t 4 -0 -r 2005 -c 1 /dev/ttyUSB0 0x42 . . . Protocol configuration: Modbus RTU Slave configuration...: address = 42, start reference = 2002 (PDU), count = 1 Communication.........: /dev/ttyUSB0, 9600, 8, 1, even, t/o 1.00 s, poll rate 1000 ms Data type.............: 16-bit register, output (holding) register table Written 1 reference.

7. And finally we will reboot the device, for the changes to take effect

   Code Block
   root@ubuntu:/# modpoll -a 42 -b 9600 -d 8 -p even -s 1 -t 4 -0 -r 2005 -c 1 /dev/ttyUSB0 0x24 . . . Protocol configuration: Modbus RTU Slave configuration...: address = 42, start reference = 2002 (PDU), count = 1 Communication.........: /dev/ttyUSB0, 9600, 8, 1, even, t/o 1.00 s, poll rate 1000 ms Data type.............: 16-bit register, output (holding) register table Written 1 reference.

8. Now we can check if the changes were done correctly

   Code Block

   root@ubuntu:/# modpoll -a 42 -b 9600 -d 8 -p none -s 1 -t 4 -0 -r 2002 -c 1 /dev/ttyUSB0 . . . Protocol configuration: Modbus RTU Slave configuration...: address = 42, start reference = 2002 (PDU), count = 1 Communication.........: /dev/ttyUSB0, 9600, 8, 1, even, t/o 1.00 s, poll rate 1000 ms Data type.............: 16-bit register, output (holding) register table -- Polling slave... (Ctrl-C to stop) [2002]: 1

    

    

    

    

    

    

./modpoll  -a 42 -b 9600 -d8 -p even -s 1 -t3 -0 -r 1000 -c 1 /dev/ttyS1

./modpoll  -a 42 -b 9600 -d8 -p even -s 1 -t4 -0 -r 2002 -c 1 /dev/ttyS1

./modpoll  -a 42 -b 9600 -d8 -p even -s 1 -t4 -0 -r 2002 -c 1 /dev/ttyS1 1

./modpoll  -a 42 -b 9600 -d8 -p even -s 1 -t4 -0 -r 2005 -c 1 /dev/ttyS1 0x42

./modpoll  -a 42 -b 9600 -d8 -p even -s 1 -t4 -0 -r 2005 -c 1 /dev/ttyS1 0x24

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