Operation Of The Force Function - Siemens S7-1200 System Manual

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14.11 Monitoring and modifying values in the CPU
14.11.5.2

Operation of the Force function

The CPU allows you to force input and output point(s) by specifying the physical input or
output address (I_:P or Q_:P) in the force table and then starting the force function.
In the program, reads of physical inputs are overwritten by the forced value. The program
uses the forced value in processing. When the program writes a physical output, the output
value is overwritten by the force value. The forced value appears at the physical output and
is used by the process.
When an input or output is forced in the force table, the force actions become part of the
user program. Even though the programming software has been closed, the force selections
remain active in the operating CPU program until they are cleared by going online with the
programming software and stopping the force function. Programs with forced points loaded
on another CPU from a memory card will continue to force the points selected in the
program.
If the CPU is executing the user program from a write-protected memory card, you cannot
initiate or change the forcing of I/O from a watch table because you cannot override the
values in the write-protected user program. Any attempt to force the write-protected values
generates an error. If you use a memory card to transfer a user program, any forced
elements on that memory card will be transferred to the CPU.
Note
Digital I/O points assigned to HSC, PWM, and PTO cannot be forced
The digital I/O points used by the high-speed counter (HSC), pulse-width modulation (PWM),
and pulse-train output (PTO) devices are assigned during device configuration. When digital
I/O point addresses are assigned to these devices, the values of the assigned I/O point
addresses cannot be modified by the force function of the force table.
802
S7-1200 Programmable controller
System Manual, 03/2014, A5E02486680-AG