CTD
Count Down
- Library:
Description
The CTD block implements the CTD ladder 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 for representing all 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 | 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' |