Calling Subroutines

Introduction

Calling subroutines is managed by 3 function blocks:

L9_JSR
L9_LAB
L9_RET

For detailed information please refer to the function block descriptions.

Up to 1023 subroutines can be established.

Control Expert does not support interrupt handling with LL984 subroutines.

Restrictions

For the calling subroutines feature the following restrictions apply:

Only one LL984 segment can be created inside the subroutine (SR Section) node of the MAST task.
L9_LAB and L9_RET function blocks can only be placed in an LL984 subroutine network in the SR Sections.
An L9_LAB function block can only be placed in row 1, column 1 of an LL984 subroutine network.

Subroutine Structure

A subroutine is identified by a number (1.. 1023).

Subroutines are called by the L9_JSR function block within an LL984 network (normal or subroutine network).

Two additional function blocks, which are only available in subroutine networks, mark the starting point (L9_LAB function block) and ending point (L9_RET function block) of a subroutine.

A subroutine may span multiple networks.

The L9_RET function block is optional and this explicit ending point of a subroutine can be omitted,

if the last subroutine network is the last network of the subroutine segment or
if a new subroutine network (L9_LAB) would entered.

The L9_RET function block or the implicit forms, return from the current subroutine network to the calling L9_JSR function block with an OK status.

Nesting

A subroutine may call other subroutines or recursively call itself up to 100 times.

If the maximum nesting level is reached, an implicit return is performed and the ERR output of the L9_JSR function block is set.

A nesting level problem message is propagated to the (99) cascaded L9_JSR function blocks.

Further cascaded L9_JSR function blocks, which are being executed after a nesting level problem, do not succeed to call a subroutine and the ERR output is being set until the nesting level stack has been unwound.

NOTE: The message is only visible at those L9_JSR function blocks, contributing to the problem. A dedicated problem treatment is possible on each calling level. Subsequent L9_JSR function blocks of a segment are not influenced by this problem.

Please also refer to the L9_JSR function block description.