Siemens SINUMERIK 828D Training Manual page 147

Libraries
Interrupt routine INT_100 & INT_101
The S7-200 PLC works cyclically, at the beginning of the scan the status of the
inputs is copied to the Process Image Table (Inputs). This is then applied to the
user PLC logic. The Subroutines are processed in the order they appear in
OB1. This means that, for example an output set early in the scan might be
reset later in the scan. It is the command that appears later in the scan that
takes precedent.
When the scan is complete the results are transferred to the Process Image
Table (Outputs) which is then physically output to the machine periphery
devices.
The diagram below shows the position of the Interrupt Blocks INT_100 and
INT_101.
Their position enables them to be used to influence the state of the inputs and
outputs without making changes to the main user programme.
Process Image Table (Inputs)
Interrupt INT_100
Main Routine OB1
Interrupt INT_101
Process Image Table (Outputs)
SINUMERIK 828D
Beginning
Of
Scan
At the beginning of the scan, the status of
the inputs is transferred to the Process
Image Table
The INT_100 interrupt block can be used to
influence the Process Image Table (Inputs)
Subroutine
Subroutine
Subroutine
Subroutine
Subroutine
The INT_101 interrupt block can be used to
Influence the Process Image Table
At the end of the scan, the status of the
outputs is transferred to the Process Image
End
Of
Scan
Page 33
Subroutines are processed
in the order they appear in
OB1
(Outputs)
Table
Section 2
Notes
B019
B019