Modbus Exception Code (communication with an Inline bus coupler for Ethernet)

Question

Hi,
I have an Inline bus coupler for Ethernet (IL ETH BK DI8 DO4 2TX-PAC: http://select.phoenixcontact.com/phoenix/dwl/dwl13a.jsp?fct=dwl&asid=907909&name=db_en_il_eth_bk_di8... see page 23) and I want to communicate with it via modbus protocol.
In the manual, it says that the Modbus register for the local digital inputs is 8000. I use the MB Ethernet Example Master.vi in the Modbus Library in LabVIEW (Function code = Read Holding Register (3), Start address = 8000, Quantity = 2). It works the first time.
My problem is when I want to write into a register. In the manual, it says that the modbus register is (8001+X, and X=number of words). So I put these input: Function code = Write Holding Register (16), Start address = 8003, Quantity = 2). When I do that, I have an Exception Code 2, and I think it means that the address is not allowable. I've try several address and several function code and I always get exception code 2, 3 or 4...
I don't understand why read works but not write.
Can anyone help me please? I try to contact Phoenix Contact but the guy who can help me will be back at his office only next wednesday.
Thank you very much
Stephanie
Attachments:
test module modbus io.vi ‏30 KB

Answer 1

Hi,
Thank you for your answer,
What do you mean by "bus" inputs and "bus" output? I know that I have 4 digital outputs (DO4) and 8 digital inputs (DI8) but I don't know how many bus that I have. I can connect to the module with its IP address, but in the page I don't have much information. This may be interesting:
  <IL_STATION>
  <IL_BUS_TERMINAL>
   <TERMINAL_TYPE>IL ETH BK</TERMINAL_TYPE>
   <NAME>IL ETH BK DI8 DO4 2TX-PAC</NAME>
   <IP_ADDRESS>192.168.168.176</IP_ADDRESS>
   <MODULE_NUMBER>2</MODULE_NUMBER>
   <DIAGNOSTIC_STATUS_REGISTER>224</DIAGNOSTIC_STATUS_REGISTER>
   <DIAGNOSTIC_PARAMETER_REGISTER>0</DIAGNOSTIC_PARAMETER_REGISTER>
  </IL_BUS_TERMINAL>
  <IL_BUS>
  <IL_MODULE number="1">
   <MODULE_TYPE>DO</MODULE_TYPE>
   <PD_CHANNELS>4</PD_CHANNELS>
   <PD_WORDS>1</PD_WORDS>
   <PD_OUT word="1">0</PD_OUT>
  </IL_MODULE>
 <IL_MODULE number="2">
   <MODULE_TYPE>DI</MODULE_TYPE>
   <PD_CHANNELS>8</PD_CHANNELS>
   <PD_WORDS>1</PD_WORDS>
   <PD_IN word="1">0</PD_IN>
  </IL_MODULE>
  </IL_BUS>
  </IL_STATION>
PD_Channel: Number of process data channels in an Inline terminal.
PD_Words: Number of process data words in an Inline terminal.
I just tried to change quantity to 1 (because PD_words = 1), change the data array with one index, change the start address (8000 to 8035), function code to 16 and it says exception code 2 except for address 8001 (exception code 4: slave device failure).
Today I did what you suggest (incrementing the starting address (0 to 100 000) and I found some address without the errors... but these address are for the special registers (like modbus connection monitoring timeout, command register, process data watchdog timeout...).
I also did what you suggest about changing the stacked sequences to flat sequences and remove the outer sequence. Didn't really solve my problem hehe
Thank you for your time
Stephanie