Siemens FC and FB instructions

[helphelphelp]

Hello, I am very new to Siemens troubleshooting, I had previously only worked with Allen Bradley. I would like to get more understanding on how to trouble shoot FC instructions and what the difference is between an FC and an FB? Is there any way to open an FC instruction like I would an AOI in Allen Bradley to see the logic inside that block? If so how would I go about doing that?

Any help is appreciated.

Thanks!

 

[L D[AR2P#0.0]]

Which platform - Simatic manager or TIA?

 

[Kelkoon]

FC an FB

Hi,


I've nver used Allen-Bradley so I can't compare with them. I'd describe them as follows:



FC are functions that take inputs and write to outputs lika a function in C or other programming language. Inside of the FC you can use only the block inputs and outputs (and get a reusable block) ou use Flags (Mxx.x), Inputs (Ixx.x), Outputs (Qxx.x) or external datablocks (DBxx.DBxxx.x).


If the block needs to be reusable (i.e. a Motor block) you would need to use a lot of Inputs and Outputs to keep the internal state of the block.


FBs a functions that in every use (i.e. for each motor) have a different datablock (DB) that keeps the internal state of that call.


Best regards,
Kelkoon

 

[JesperMP]

Yes you can open FBs and FCs, unless they are protected blocks.
Google "Siemens STEP7 getting started" and you should get tons of links inkl. youtube videos. There is a big difference between the older STEP7 'Classic' for S7-300/400 and the newer TIA portal for S7-1200/1500, so you must distinguish between these TIA can also be used for S7-300/400, but that is a can of worms.

As to "what the difference is between an FC and an FB?".
An FC does not have memory by itself. A rookie mistake is to use TEMPs in the FC and assume that these are retained between scans. All the IO and the other memory must be passed in and out of the FC.
An FB is like an FC, except it has its own memory (called STATs). Because of the memory, every call of an FB must have an instance-DB (IDB) assigned to it.
Think of the FB+IDB as an 'object'.

 

[cardosocea]

An FB is what AOI's in Rockwell should be.
An FC is what subroutines with parameters in Rockwell attempt to be.

Hopefully this makes it clearer?

 

[p8p8]

Hello, I am very new to Siemens troubleshooting, I had previously only worked with Allen Bradley. I would like to get more understanding on how to trouble shoot FC instructions and what the difference is between an FC and an FB? Is there any way to open an FC instruction like I would an AOI in Allen Bradley to see the logic inside that block? If so how would I go about doing that?

Any help is appreciated.

Thanks!

Function Block is like AOI. You can create and edit FB

 

[helphelphelp]

I’m not sure if it’s somatic or TIA. It’s about 12 years old so I assume simatic? Basically the problem I’m running into is seeing lots of FC instructions with all the inputs and outputs but not sure of exactly how to read these instructions for troubleshooting. I’m an electrician who can read ladder diagrams but never had the experience programming. I’m only a troubleshooter essentially.

 

[kalabdel]

I’m not sure if it’s somatic or TIA. It’s about 12 years old so I assume simatic? Basically the problem I’m running into is seeing lots of FC instructions with all the inputs and outputs but not sure of exactly how to read these instructions for troubleshooting. I’m an electrician who can read ladder diagrams but never had the experience programming. I’m only a troubleshooter essentially.

If you're intention is to learn then there's plenty of resources to get you on your way.
If you are troubleshooting something and need timely help the post screenshots and we're likely to ask for more specific screenshots afterwards to help you out.