I have an S7-317-2 DP PLC that I want to pull information from it without interfering with the code and the hardware. The PLC is belong to a system that cannot be altered for safety reasons.

The PLC is set up currently as a Profibus Slave. I need to read information from it using another S7-300 PLC, that I have simulated on my desk with an S7-317 2 PN/DP. I have set this up as a Profibus Master and i have added the S7-317-2 DP to the hardware and run a Profibus cable between each of them. They are linked together now with no bus faults.

I am attempting to use the SFC 72 (I_GET) from the Master to pull information from the Slave, but I am having problems with the set-up of the adresses. The help on this SFC is very basic and doesn't help me.My SFC is attached below.

Hello Brian;

You can use S7 Basic Connections and communication blocks only if both CPUs are configured as DP-masters. And if each PLC has a CP 342-5 inserted in the rack and configuration.

If one is master and the other one slave, you must use master-slave acyclic data exchanges. And the interface areas of the slave must be configured for this data exchange. See fig. 3 in the following FAQ (and sample program):

DP link between CPU 315-2DP (slave) and S7-400 (master) with STEP 7 V5.3

https://support.industry.siemens.com/cs/ww/en/view/6518822

If you cannot change the slave PLC's configuration, you might have a little problem...

You might want to look into using OPC to read/write between the 2 CPUs in that case.

Hope this helps,

Daniel Chartier

Thanks for your reply.

i have to use Profibus communications, and as a result I cannot use OPC comms. If i can add a n FC to the Slave PLC, would it be advisable to use I_PUT and I_GET to transfer data?