The CTD block implements the
CTD ladder logic
instruction. When the rung conditions are true, the block counts downwards.
EnableIn— Enable Input
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.
CD— Count Down Enable Output
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.
Counter Tag— Counter Structure
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
size. To change the attributes of the
Operand Tag, open the Program Variables table
within the Ladder Diagram Program block. The
of the timer tag is of the
Bus:COUNTER type with its initial value
specified as a structure containing the following fields:
The preset value specifies the value which the accumulated value must reach before the instruction indicates it is done
The accumulated value specifies the number of transitions the instruction has counted.
The count up enable contains
Count down enabled.
The done bit when set indicates the counting operation is complete
The overflow bit when set indicates the counter incremented past the upper limit of 2,147,483,647
The underflow when set indicates the counter decremented past the lower limit of -2,147,483,648.
|Type: character vector|
|Value: character vector|