CTD block

Short summary

Name	`CTD`
→POU type	→function block
Category	Standard (safe), Counter
Conform to →IEC-standard	no restrictions
Graphical interface
Available since	version 1.4.1 (for Neuron Power Engineer) - initial variant version 3.8.0 (for library `Standard (safe)`): block provided in this library

Functionality

The block is a down-counter (for INT values).

If there is a positive →edge at input CD, the counter is activated and decrements the counter value by 1. If input LD is →turned on, the counter value is reset to the initial value entered at PV. If the counter value reaches or falls below 0, output Q is set to value TRUE (or an equivalent). The decrementing is stopped, if the lower limit of INT (= value -32,768) is reached. Output CV returns the current counter value of the block.

In-/outputs

	Identifier	→Data type	Description
Inputs:	`CD`	`BOOL`	decrement in case of positive edge
	`LD`	`BOOL`	flag for reset to value of `PV`
	`PV`	`INT`	initial value for counting
Outputs:	`Q`	`BOOL`	flag showing whether value `0` is reached or not
Outputs:	`CV`	`INT`	current counter value

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

See:

"Blocks for safe logic" whether this block is supported for developing safety-relevant applications.
"Highlighting safe logic in the FBD-editor" for the effects when using the block as a block for safe logic.

Example for usage within ST-editor

PROGRAM Test

VAR

        myCTD          : CTD;

        StartCounter   : BOOL;

        RestartCounter : BOOL;

        out            : BOOL;

        counter        : INT;

    END_VAR

    myCTD(CD := StartCounter, LD := RestartCounter, PV := 10, Q => out, CV => counter);

    (* Instance of block 'CTD' is called: The counter is activated, when 'StartCounter' is 'TRUE'. The value for counting is reset to '10', when 'RestartCounter' is 'TRUE'. *)

    (* Appropriate variables access the outputs. *)

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.