Siemens S7 SFC20

Plc_User

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Dec 2005
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Can I be sure when I use SFC20 Blockmove in my programm that when the plc has processed the call to the Blockmove and now continues with the next instruction underneath the Blockmove that Blockmove is totally completed? Is it reayly a 'synchronous function'?
 
Hi I dont know the amswer but check help files.

Secondly, how about usin a bit (last of the block move data) as a check bit?

Reset last bit in target data
run sfc20
check to see if last bit of dest is achieved
set last target bit in target data
 
plc_user,
PLC will always go down from top scanning instructions inbetween in order. SFC20 is also a set of instruction in a packaged form, so all instructions in SFC 20 is done with when instructions after SFC20 comes. This is true for all PLC's.
 
If i remember well the function can be interupted when you have OB35... running, Without checking if i recall well there is a UBlockmove SFC/B8x (81?)
If i'm wrong sorry for the bad info
 
Last edited:
Functions dont have own memory, thus they cant be "asynchronous" as there cant be knowledge of state other than current function call. They can be interrupted by higher priority process tough. So if you dont need data from place where it is transferred to in higher interrupt program, you can safely trust that all data is transferred after function has finished excecuting.

Function Blocks in otherhand have own memory and thus can be "asynchronous".
 
Plc_User said:
Can I be sure when I use SFC20 Blockmove in my programm that when the plc has processed the call to the Blockmove and now continues with the next instruction underneath the Blockmove that Blockmove is totally completed? Is it reayly a 'synchronous function'?
Click to expand...

Yes, but why do you ask ?
 
you could always evaluate the return value, usually problems here are at the design stage though - Help file details the various codes and meaning.
 
TurpoUrpo said:
Functions dont have own memory, thus they cant be "asynchronous" as there cant be knowledge of state other than current function call. They can be interrupted by higher priority process tough. So if you dont need data from place where it is transferred to in higher interrupt program, you can safely trust that all data is transferred after function has finished excecuting.

Function Blocks in otherhand have own memory and thus can be "asynchronous".
Click to expand...

See SFC51 for example.
 

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