Short summary

Name	`TOF`
→POU type	→function block
Category	IEC-block, Timer
Conform to →IEC-standard	no restrictions
Graphical interface
Available since	version 1.4.1 (for logi.CAD 3)

Functionality

This is an edge delay where the turning-off edge is delayed.

Enter the delay period at input PT. If input IN is →turned on, output Q returns value TRUE (or an equivalent). If input IN is →turned off and the delay period is over, output Q returns FALSE (or an equivalent). Output ET returns the expired time since turning input IN off, until the value entered at PT is reached and as long as the input IN is turned off.

Implementer-specific realization

The IEC-standard does not specify whether and how to consider changes for input PT while the functionality is executed. In logi.CAD 3, the expired time is always compared with the current value of PT. Thus, if input PT is changed after input IN has been turned off, the behavior of the block is affected.

This block receives the current system time from the runtime system. This time remains constant while the same task is executed. However, in case of different tasks, it is possible that a different system time is used when the belonging programs are executed (even if the different tasks have the same cycle time).

The following illustration shows the behavior of TOF:

images/download/attachments/414782929/TOF-version-1-modificationdate-1535106743395-api-v2.png

In-/outputs

	Identifier	→Data type	Description
Inputs:	`IN`	`BOOL`	input/start
Inputs:	`PT`	`TIME`	preset time
Outputs:	`Q`	`BOOL`	output
Outputs:	`ET`	`TIME`	elapsed time

Input EN and output ENO are available when →calling the block. See "Execution control: EN, ENO" for information on input EN and output ENO.

Example for usage within ST-editor

Simple call of TOF

PROGRAM Test
    VAR
        tof1      : TOF;
        elapsed   : BOOL := TRUE;
        help      : BOOL := TRUE;
    END_VAR
    tof1(IN := help, PT := T#2s, Q => elapsed);
    (* Instance of block 'TOF' is called. Variable 'elapsed' is set to FALSE after 2 seconds, right after you set 'help' to FALSE . *)
END_PROGRAM

When creating your application within the ST-editor, enter a call of a block by typing the text as requested by the syntax or use Content Assist.