Hello Everyone;

I try to convert program S7-300 to s7-1500.But I have a problem in FB , on the picture network-1 fb start with;

Now my question is exactly like this; It started with SRD function in the first line of fb's first network. Since there is no variable before it, I could not understand what it does SRD. In addition, when I watched the cpu online, I could not understand what was written to accumulator-1. Can you help me understand this? I reviewed the stl manual. However, I could not understand what it means to use it in this way at the entrance of fb.

Thanks in advance for your support

Hi S7_Savas

this is nasty programming and most likely not done because it is efficient or good, but rather because it can be done.

Put simple, every FB211 call from within FB310 passes on a pointer value for it ValveStatus parameter.

In the first FB211 call (for V_VA510), this is P#DB20.DBX120.0. 

accu1 does - for better or worse - now contain the pointers memory area and Byte.Bit address (i.e . 840003c0 in this example).

SRD3 gets rid of the bit address so you are left with 78(hex) = 120(int).

This value is now compared with the value in DB20.DBW2 ("Nr_VM") which is presumably entered from the HMI (or comes from drop down text list) and the block then controls that valve as per HMI commands. 

None of this rubbish programming would be required if they simply had added another INT input parameter to FB211 were you supply it with it valve number (e.g. 120 in this example) and use it for the comparison with the HMI valve number.

This is the fix I suggest you apply now that it is in an S7-1500.  

@fritz

Thanks for support. I understand this. Problem solved.