Description
The "Configure time delay" instruction pauses the program execution for a specific period of time. You indicate the period of time in microseconds on the WT parameter of the instruction.
You can configure time delays from -32768 up to +32767 microseconds (μs). The smallest possible delay time depends on the CPU and corresponds to the execution time of the instruction.
The execution of the instruction can be interrupted by higher priority events and does not return any error information.
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Note Negative delay time If you specify a negative delay time at parameter WT, the enable output ENO, or the RLO and the BR bit, will return the signal state FALSE. A negative delay time does not affect the CPU. The following instructions linked to enable output ENO are not executed in LAD or FBD. |
Parameters
The following table shows the parameters of the "Configure time delay" instruction:
|
Parameter |
Declaration |
Data type |
Memory area |
Description |
|---|---|---|---|---|
|
EN |
Input |
BOOL |
I, Q, M, D, L, T, C or constant |
Enable input |
|
ENO |
Output |
BOOL |
I, Q, M, D, L |
Enable output |
|
WT |
Input |
INT |
I, Q, M, D, L, P or constant |
Time delay in microseconds (μs) |
Example of the influence of the planned delay time
In the following example, you will see the influence of the delay time of the instruction "WAIT" in various scenarios.
The following figure is a schematic representation of the scenarios:
Remaining time = The period between the end of the planned delay time (via "WAIT") until the end of the interrupt OB
Excess time = The period between the end of the interrupt OB and the end of the planned delay time (via "WAIT").
Case 1:
The "WAIT" instruction is called in an OB1. The "WAIT" instruction can be interrupted by higher-priority OBs or higher-priority processes (e.g. System Threads). However, the delay time of the "WAIT" instruction is neither changed nor deferred.
Cases 2 and 3:
Processing of the program in OB1 is resumed after a time delay of 20 ms. This time delay is calculated by calling the "WAIT" instruction in OB1 (see OB1 with WAIT). Within these 20 ms, an interrupt OB can run its own program code. The send clock of the CPU is not changed.
Case 4:
Processing of the program in OB1 is resumed after the higher-priority process has ended. The 20 ms delay time in OB1 has elapsed, but the higher-priority process still needs to be ended. The send clock of the CPU is increased.
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Note Order of execution of system or communication processes (System Threads) The System Threads usually use the priority "15". There are also System Threads with a higher priority than "26", but these processes cause a lower CPU load. System Threads are not displayed in the figure. |
Runtime measurement of the OB1 using the "RT_INFO" instruction:
Case 2: 20 ms - 8 ms - System Threads = <12 ms. Send clock: ~20 ms.
Case 3: 20 ms - 11 ms - System Threads - <9 ms. Send clock: ~20 ms.
Case 4: 20 ms - 15 ms - System Threads - <7 ms. Send clock: ~22 ms.