Flash Memory; Controlling The Execution Of A Program; Calling A Subroutine Block; Creating A Temporary End Of Logic - GE VersaMax PLC User Manual

7.4 Flash Memory

7.5 Controlling the Execution of a Program

CPU Operation
For public disclosure
A VersaMax PLC stores the current configuration and application in nonvolatile
battery-backed RAM. The programmer software can be used to store a copy of the current
configuration, application program, and reference tables (excluding overrides) to Flash
memory. The programmer can also be used to read a previously-stored configuration,
application program, or reference tables from Flash into RAM, or to verify that Flash and
RAM contain identical data.
By default, the PLC reads the configuration, program logic, and reference tables from
RAM at powerup. However, it can be configured to read them from Flash. This is
recommended, because data in Flash is non-volatile, even in the case of a battery failure.
The VersaMax CPU Instruction Set contains several powerful Control functions that can
be included in an application program to limit or change the way the CPU executes the
program and scans I/O.

7.5.1 Calling a Subroutine Block

The CALL function can be used to cause program execution to go to a specific
subroutine. Conditional logic placed before the Call function controls the circumstances
under which the CPU performs the subroutine logic. After the subroutine is finished,
program execution resumes at the point in the logic directly after the CALL instruction.

7.5.2 Creating a Temporary End of Logic

The END function can be used to provide a temporary end of logic. It can be placed
anywhere in a program. No logic beyond the END function is executed, and program
execution goes directly back to the beginning. This ability makes the END function useful
for debugging a program.
The END function should not be placed in logic associated with or called by a Sequential
Function Chart control structure. If this occurs, the PLC will be placed in STOP/FAULT
mode at the end of the current sweep and an SFC_END fault will be logged.
7.5.3 Executing Rungs of Logic without Logical
Power Flow
The nested Master Control Relay can be used to execute a portion of the program logic
with no logical power flow. Logic is executed in a forward direction and coils in that part
of the program are executed with negative power flow. Master Control Relay functions
can be nested to 8 levels deep.

7.5.4 Jumping to Another Part of the Program

The Jump function can be used to cause program execution to move either forward or
backward in the logic. When a nested Jump function is active, the coils in the part of the
program that is skipped are left in their previous states (not executed with negative power
flow, as they are with a Master Control Relay). Jump functions can also be nested. Jumps
cannot span blocks, SFC actions, SFC transitions, or SFC pre- or post-processing logic.
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