Internet PLC Forum

General => Technical support => Topic started by: EDGAR on December 03, 2014, 11:26:46 AM

Title: ReadMB2
Post by: EDGAR on December 03, 2014, 11:26:46 AM

Hi,
We are in the process of designing a Modbus slave web service over Modbus tcp but we are getting strange behavior on the plc side. Hope you can help us find the problem.

Here's the PLC code

S = STATUS(3)
if(S = 1) THEN PRINT #4 "</>" ENDIF
 
  //CONNECT TO THE REMOTE DEVICE
  PRINT #4 "<MBTCPCONNECT IPAddress:502>"
  Call wait4conn  //WAIT FOR CONNECTION
  //GET CONNECTION STATUS
  S = STATUS(3)  //S=1 = CONNECTED, S=0 = NOT CONNECTED      
   

   IF S = 1 THEN
      setlcd 2,1, "Reading TEMP...      "  
      READMB2 4,1,40004,DM[151],2
      //DM[153] = ReadModbus(4,1,4)
      N$ = "Waiting response....."
      Call WaitForDataInD
      IF STATUS(2) = 0 THEN
         f$ = input$(4)
         DM[151]=999
         DM[152]=999
         setlcd 2,1, "Reading TEMP failed!!!!   "
      ELSE
         setlcd 2,1, "Reading TEMP success!!!!!"
      ENDIF
       PRINT #4 "</>"
   ENDIF

The actual stream of two requests between the PLC and the slave service is below:

At the ModbusSlave web Service:
Recv From PLC: 006700000006 01 04 9C 44 00 02 | Send From WebSVC: 006700000007 01 04 04 00 00 42 34

Recv From PLC: 008D00000006 01 04 9C 44 00 02 | Send From WebSVC: 008D00000007 01 04 04 00 00 42 34

I can't see where is failing...

Title: Re:ReadMB2
Post by: EDGAR on December 03, 2014, 11:29:54 AM

Sorry pressed enter too soon.

We even added a chr 10 and 13 at the end of the byte just in case the plc is looking for that but is not working anyway.

We will keep trying and update later tonight...

Thanks,
Ed

Title: Re:ReadMB2
Post by: EDGAR on December 03, 2014, 11:52:14 AM

I just changed the address from 40004 to 30004 thinking that may be causing register overflow but nothing yet. Still having the issue...

Thanks,
Ed

Title: Re:ReadMB2
Post by: EDGAR on December 03, 2014, 03:27:27 PM

This is what I found using a third party testing software... Image attached...

Title: Re:ReadMB2
Post by: EDGAR on December 03, 2014, 07:17:24 PM

Ok, I have not found the issue but the problem is in the PLC program that's currently running. I tested with the Ethernet Modbus sample and everything works great!

So keep everyone posted when I find the solution...

Thanks,
Ed

PS: the image was never uploaded on the previous post, it was too large...

Title: Re:ReadMB2
Post by: support on December 03, 2014, 08:04:44 PM

I think you are trying to read from Modicon address 40004 - this means you should be reading from binary address = 40004-40001 = 3.

Try reading from address 3 and see if you get your expected result.

Title: Re:ReadMB2
Post by: EDGAR on December 04, 2014, 06:05:59 AM

Thank you! It works great using the sample project that comes with your programming software. I will make changes to the current program to see if it works.

Thanks, again and keep you posted.
Ed