CTD

Count Down

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Libraries:

Description

The CTD block implements the CTD ladder logic instruction. When the rung conditions are true, the block counts downwards.

Ports

Input

EnableIn — Enable Input

off (default) | on

Controls the execution of the block. EnableIn reflects the rung state preceding the block. If the rung state preceding the block is false, EnableIn is false, the block does not execute and the outputs are not updated.

Output

CD — Count Down Enable Output

off (default) | on

The count down enable output contains the rung-in condition when the instruction was last executed. By default, CD follows the state of EnableIn. If the EnableIn input to the block is false, the logic implemented by the block is not executed and CD signal is set to false.

Parameters

Counter Tag — Counter Structure

C (default) | character vector

Specify the counter parameters in the format of tags. In Ladder Diagrams, tags (variables) are used to represent inputs, outputs, and internal memory with attributes such as Data Type, Initial Value, and size. To change the attributes of the Operand Tag, open the Program Variables table within the Ladder Diagram Program block. The Data Type of the timer tag is of the Bus:COUNTER type with its initial value specified as a structure containing the following fields:

Field	Description	Default Value
PRE	The preset value specifies the value which the accumulated value must reach before the instruction indicates it is done	0
ACC	The accumulated value specifies the number of transitions the instruction has counted.	0
CU	The count up enable contains rung-condition-in when the instruction was last executed.	1
CD	Count down enabled.	1
DN	The done bit when set indicates the counting operation is complete	0
OV	The overflow bit when set indicates the counter incremented past the upper limit of 2,147,483,647	0
UN	The underflow when set indicates the counter decremented past the lower limit of -2,147,483,648.	0

Programmatic Use

Block Parameter: PLCOperandTag

Type: character vector

Value: character vector

Default: 'T'

Version History

Introduced in R2019a