4. INITIAL PROGRAMMING
Moreover, the forced writing command (F7) writes a value into a variable without allowing this value to be changed until
the forced variables are released.
It is important to highlight that, when used the MODBUS RTU Slave and the MODBUS Ethernet Server, and the Read-only
option from the configured relations is not selected, the forced writing command (F7) must be done over the available variables
in the monitoring window as the writing command (CTRL + F7) leaves the variables to be overwritten when new readings are
done.
ATTENTION
The variables forcing can be done in Online mode.
Diagnostic variables cannot be forced, only written, because diagnostics are provided by the
CPU and will be overwritten by it.
When a forced writing is performed in a redundant variable of the Active PLC, the application’s MainTask will suffer
an impact on its execution time, both in the Active PLC and in the Reserve PLC. This is because the two Half-Clusters will
exchange information about the forced variables every cycle. Therefore, when forcing variables in a redundant system, the
addition that the task execution can have must be considered. The table below exemplifies how much will be increased, on
average, in the execution of MainTask when this occurs:
Active CP Reserve CP
Runtime 50 ms 100 ms 200 ms 50 ms 100 ms 200 ms
Addition with 10 forces 2,4 % 2,2 % 1,7 % 4,0 % 3,4 % 2,0 %
Add to 50 forces 12,0 % 9,2 % 6,0 % 18,0 % 12,0 % 8,0 %
Add with 128 forcings 26,0 % 21,0 % 16,0 % 56,0 % 34,0 % 22,5 %
Table 41: Influence of Forcing Variables on a Redundant CP
ATTENTION
When a CPU is with forced variables and it is de-energized, the variables will lose the forc-
ing in the next initialization.
The limit of forcing for the Nexto CPUs is 128 variables, regardless of model or configura-
tion of CPU used.
4.11. Logout
To finalize the online communication with the CPU, the command Logout must be executed, located in the Online menu,
as shown on figure below.
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