Problem with MODBUSPN block and MODBUS communication

Dear Siemens wizards,

I'm working on an old system where a 315CPU is talking with a cummins motor over modbus via a modg-100 accespoint from PROCONX. The system hasn't work that I know of for atleast 4-5 years. 

After testing some stuff and asking the support of ProconX for any advice I came to installing an empty CPU with just the bare ModbusPN blocks as per the example project. I was, after some fiddling around, able to setup a live connection with the MODG-100 module. But after trying a lot of different things, I am still not able to get the data transfering working. 

-CPU is a 315-2 PN/DP
-In the control_status DB is get the following status codes; 
        CONN_ESTABLISHED - TRUE
        ERROR - FALSE
        STATUS_MODBUS - A090 (which indicates a missing or incorrect license. The manual mentioned that a missing or incorrect license shouldn't disrupt communication)
        STATUS_CONN - 0
        STATUS_FUNC - ' ' (empty string)
-In the modg-100 webbrowser I can't see any requests from CPU
-Using Modbus Slave tool and wireshark, I can't see any communication between client and server.

Any help would be appreciated. I've never worked with modbus before and I'm not too familiar with SIMATIC or ProconX. 

Thanks for your response!

I set and reset the ENQ_ENR each cycle. It is always true when the block is called (which is each cycle).

If telegrams are datatransfer requests, then yes.

It sometimes is unclear to me what is exactly happening due to the gateway that is in between the client and server. The gateway converts the Modbus/TCP to Modbus RS485.

As far as I know, the MODBUSPN is called each cycle with the correct IP adress for the gateway and with ENQ_ENR being TRUE. First I wasn't able to setup a connection, but after configuring the correct addresses this was fixxed. I hoped it then would just be a matter of sending requests with the correct start addres, length and ID, but unfortunatly this isn't the case. 

 Thanks for your response!

Wüstenräuber

Have a look at the example projects, which are installed during the product installation. Here you can see the handling of ENQ_ENR.

 I am using the ModbusPN example project. So my usage of ENQ_ENR should be correct seeing I just uncommented some lines regarding this bit. 

Wüstenräuber

With the wizard you define the parameter datablock, which modbus registers and which datablocks the modbus block should know and should handle. It is not the job list for a communication during runtime.

 I used the wizard and seeing I'm using a modbus slave on my pc for testing purposes, I just use the same settings as I set in the ModbusPN wizard.

Wüstenräuber

For a telegram you must set the runtime parameter on the modbus block during runtime.

 I don't understand this last part. Is the runtime parameter the ENQ_ENR bit?

 Thanks again!

The situation I have setup right now;
- The ENQ_ENR is always TRUE when block is run 
- UNIT (the modbus unit number of the server) is a constant. Same goes for DATA_TYPE, START_ADDRESS AND LENGTH
- I'm unsure what to do with WRITE_READ. I can't seem to find how this is used. Is it FALSE for WRITE and TRUE for READ?