Special Function Programs

The controller compiles all SF programs and subroutines. 

They are compiled in the following situations:

• When a user program is downloaded to the PLC, if the SF Program or subroutine is enabled,

• When the SF program or subroutine is enabled, if the SF program has been modified,

• During a Power Up start (following the application of power).

Programs that contain errors will not be enabled. During a program download, Workshop will

display a message indicating the error. Once you acknowledge the message,

the download will continue, leaving the program disabled. You must correct the programming

error before the program or subroutine can be enabled. User Programs originally written

for the Simatic® 505 PLC may contain undetected errors, if the programs were not originally compiled.

This can occur because the SF interpreter never attempts to execute the instruction

due to the branching logic. A common problem is that additional ENDIF statements are included

or the correct number of ENDIF statements is not present.

Unlike the Simatic® 555. there are no restrictions regarding the instructions that

can be used in a compiled program.