8.12 Initiating a process interrupt
Introduction
For the individual counters of the FM 450-1 you can set which events are to trigger a hardware
interrupt during operation. For this purpose you parameterize the counter interrupts in the
parameter assignment screen marks.
What is a hardware interrupt?
If a response is to be made to an event regardless of the cycle of the CPU, each counter of the FM
450-1 can trigger a hardware interrupt. The CPU then interrupts the cyclical program and
handles the hardware interrupt OB.
Which events can trigger a hardware interrupt?
In the FM 450-1 count mode, the following events can trigger a hardware interrupt
(independently of each other for each of the two counters):
• Opening of the gate (in modes with HW or SW gate)
• Closing of the gate (in modes with HW or SW gate)
• Overow
• Underow
• Zero crossing
• Reaching comparison value 1 in the up direction
• Reaching comparison value 1 in the down direction
• Reaching comparison value 2 in the up direction
• Reaching comparison value 2 in the down direction
• Setting the counter with an external signal
You can select a random number of events for triggering hardware interrupts, as long as the
boundary conditions are observed.
Enabling the hardware interrupt
When conguring the hardware, in the parameter assignment screen masks you enable the
interrupts for the module and choose whether the module is to initiate a diagnostic and/ or a
hardware interrupt.
Hardware interrupt OB, OB 4x
If a hardware interrupt occurs, the user program is interrupted, the data are transferred from the
module to the start information of the OB 4x and the OB 4x is called. The hardware interrupt is
acknowledged by quitting the OB 4x.
If no OB 4x is programmed the CPU goes into STOP. If you then switch back to RUN, the hardware
interrupt requirements are deleted.
Modes, settings, parameters and commands
8.12 Initiating a process interrupt
Counter module FM 450-1
76 Equipment Manual, 03/2022, A5E03648739-AC
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