Introduction

A coil is an LL984 element which transfers the status of the horizontal link on the left side, unchanged, to the horizontal link on the right side. The status is saved in the respective Boolean actual parameter. Coils normally follow contacts or FFBs, (functions and function blocks), but they can also be followed by contacts.

Information Concerning Variables

The LL984 Editor can display various information concerning variables attached to coils, contacts and function block nodes.

This information can be displayed by tooltip, too.

For further information on how the variables attached to coils are displayed, please refer to Network Display.

Coil Types

Non-latched/ and latched coils have different behavior.

Non-latched Coils:

A reset of the coil will be performed during warm-start and after STOP/RUN of the PLC. Reset during warm-start works for %M addresses and %M-located-variables attached only.

Latched Coils:

In the first scan latched coils have the status of last scan before warm-start.

Coil Type

Description

Call via Menu Command

Call via Icon

Call via Keyboard

Coil (non-latched)

With coils, the status of the left link is copied to the relevant Boolean actual parameter and the right link.

For further information see below.

Edit > New > Coil

or

Coil from the context menu

F5

Latched coil

With latched coils, the status of the left link is copied to the relevant Boolean actual parameter and the right link.

For further information see below.

Edit > New > Latched coil

or

Latched coil from the context menu

Shift+F5

PLC Start Behavior of Coils

  • Non-latched Coils

    A reset of the coil will be performed during warm-start and after STOP/RUN of the PLC. Reset during warm-start works for %M addresses and %M-located-variables attached only.

  • Latched Coils

    Latched coils will maintain their state after a Stop/Start of the PLC and on warm-start. In the first scan latched coils have the status of last scan before warm-start.

    This is the same behavior as normal coils show in IEC Ladder Diagram language.

Detailed information:

Non-latched Coil Restriction

The following restriction applies for non-latched coils:

  • If an address (or a variable located on this address) is attached to a normal LL984 coil (non-latched) and this address has other (latched) write usages somewhere else in the program (for example an assignment in ST/FBD/LD or a latched coil in an LL984 network), this will lead to the following analyze message:

    Non-latched usage of '%1' detected, which is used also as latched.

    This message will be reported for the non-latched coil(s) usage in LL984 networks only.

    To help avoid this restriction, start a search for getting the occurrences of this conflicting address.

Latched Coil Representation

A latched coil is represented by a circle with an L or an M in the middle.

Whether an L or an M will be displayed inside a latched coil can be define via Tools > Options > Data and Languages > LL984 > Show latched coil as. Please refer to Data and Languages.