Siemens plc S7 300/400 ladder logic blocks in calling instructions

CALL in the ladder diagram coil can call functions (FC) or system functions (SFC), the call cannot be passed parameters. Calls can be unconditional, CALL directly connected to the vertical line on the left side of the coil, equivalent to UC in the statement table orders; can also be conditional, condition provided by the control CALL contact circuits of coils, equivalent to CC in the statement table instructions.

Logical block is called if you need to pass parameters, you can use the command to invoke the function block in the box. FB 3-70 box in Figure 10 is the function that is being invoked, DB3 is called FB 10 o’clock block of background data.

Conditions for return instructions (Return,RET) appears as a coil, left logic for conditional block conditions provided by the contact circuit to control it, RET coil cannot be connected directly on the left of the vertical power cord. If you call it is the unconditional return, at the end of the block does not require the use of RET instruction.

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