Short summary

Name	`SUB_DT_DT`
→POU type	→function
Category	IEC-block, Time
Conform to →IEC-standard	currently restricted (IEC demands error handling, if the result of the block exceeds the range of values for the output data type. See " No check of invalid connections " for the behavior in logi.CAD 3. )
Graphical interface
Available since	Version 1.109.0 (für logi.CAD 3)

Functionality

The block subtracts the date value (with a time of day value) entered at input IN2 from the date value (with a time of day value) entered at input IN1 (= IN1 - IN2). The block returns the result of this subtraction in format TIME.

No check of invalid connections

For some blocks, invalid connections are not checked by logi.CAD 3. Therefore, enter code in your application to detect invalid connections (e.g. IF-statements in the ST-code).

See "IEC-blocks for the application" for information what the consequences of an invalid connection might be.

An invalid connection due to →overflows or →underflows might occur during a calculation using SUB_DT_DT . As your used →target system might influence the usage of →time literals in logi.CAD 3 (see "Properties and restrictions specific to the target system") , an overflow/underflow might occur for different return values when using different target systems.

Inputs, return value

	Identifier	→Data type	Description
Inputs:	`IN1`	`DATE_AND_TIME`	1st value
Inputs:	`IN2`	`DATE_AND_TIME`	2nd value
Return value:	–	`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.

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

The calculated values are evaluated by using the Assert block .

FUNCTION_BLOCK ExampleSubDtDt
   VAR
      result : TIME;
   END_VAR
   result := SUB_DT_DT(IN1 := DT#2017-08-30-00:00:01, IN2 := DT#2017-08-29-23:59:59);
  
   Assert(result = TIME#2s);
END_FUNCTION_BLOCK

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.