Selecting Coils

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.

CAUTION

UNINTENDED EQUIPMENT OPERATION

Before using non-latched or latched coils, make sure that you completely understand the different behavior of non-latched/latched coils.
Be sure of the output states after a PLC start when using latched and non-latched coils.

Failure to follow these instructions can result in injury or equipment damage.

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:

For details when a warm-start is performed please see Processing of Power Outage and Restoral for Premium/Quantum PLCs.

Especially for the case of a Power Cycle this depends on the position of the PLC's key switch (MemPrt/Start/Stop).
- For firmware version 2.8:
  
  Latched coils are not maintained if the key switch is in the Start position.
- For firmware version 2.6:
  
  Latched coils are maintained regardless of the key switch position.
For details regarding the PLC's key switch refer to Key Switches.

For details regarding Cold Start and warm-start processing refer to Processing on Cold Start for Premium/Quantum PLCs and Processing on Warm Restart for Premium/Quantum PLCs.

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.