Technical data

Organization Blocks
System Software for S7-300/400 System and Standard Functions - Volume 1/2
1-14 A5E00709327-01
1.6 Hardware Interrupt Organization Blocks
(OB40 to OB47)
Description
S7 provides up to eight independent hardware interrupts each with its own OB.
By assigning parameters with STEP 7, you specify the following for each signal
module that will trigger hardware interrupts:
• Which channels trigger a hardware interrupt under what conditions.
• Which hardware interrupt OB is assigned to the individual groups of channels
(as default, all hardware interrupts are processed by OB40).
With CPs and FMs, you assign these parameters using their own software.
You select the priority classes for the individual hardware interrupt OBs using
STEP 7.
Understanding the Operation of Hardware Interrupt OBs
After a hardware interrupt has been triggered by the module, the operating system
identifies the slot and the corresponding hardware interrupt OB. If this OB has a
higher priority than the currently active priority class, it will be started. The channel-
specific acknowledgement is sent after this hardware interrupt OB has been
executed.
If another event that triggers a hardware interrupt occurs on the same module
during the time between identification and acknowledgement of a hardware
interrupt, the following applies:
• If the event occurs on the channel that previously triggered the hardware
interrupt, then the new interrupt is lost. This is illustrated in the following figure
based on the example of a channel of a digital input module. The triggering
event is the rising edge. The hardware interrupt OB is OB40.
Process signal
OB40
Execution of OB40
These hardware interrupts are not detected
• If the event occurs on another channel of the same module, then no hardware
interrupt can currently be triggered. This interrupt, however, is not lost, but is
triggered after the acknowledgement of the currently active hardware interrupt.