Newbie help (Siemens)

[jimmyanderson]

Hi people

I'm new to the forum and I'm in need of a little bit of advice if anyone can help, I've been tasked to make a small modification on one of our s7 300's, we currently do not have the programme for it so I have been able to create new project and upload the existing project to the new one. The question I have is that when I viewed the accessible nodes originally I noticed quite a few SFB and SFC blocks (which are protected) but when I view the blocks on the new project these haven't been uploaded, having managed to find what I'm looking for and make a small mod to one of the FC blocks when I download the programme to the PLC am I likely to download and basically screw up because there are no SFB and SFC blocks to download or are they a permanently in stored in PLC and it doesn't matter?
Thanks in advance
Jimmy

 

[sigmadelta]

Hi Jimmy,

The SFB and SFC blocks are permanent, read-only blocks in the PLC. SFBs are "System Function Blocks" and SFCs "System Functions". You cannot download them to the PLC anyway because they are read-only.

So you don't have to worry about them being missing in your project.

 

[Jeebs]

The best advice I can give you on Siemens:
Download only the blocks you have changed.
Do NOT download the entire project unless you are sure, very sure.


SFC/SFB are system blocks that are part of the CPU firmware, you cannot change them, nor delete them. So you shouldn't really fear that.
The main reason I'm saying you should only download changes, is because downloading DB's can (and will) result in very unpleasant surprises.

 

[sigmadelta]

Yes, absolutely.

I usually do "compare blocks" before I download. Right-click the Blocks folder in your offline project, and select "Compare Blocks...", and perform an offline/online comparison. You can even click the "Go to..." button to see the offline block and online block codes side by side.

 

[jimmyanderson]

Thank you for the reply to my question. I was kind of sure this was the case but needed a second opinion. I will take on board the responses, I appreciate your help.

Regards Jimmy