Siemens SIMATIC S7-400 Configuration And Use Manual page 64

Technological Functions of the S7-400
PMC (Process Monitoring and Controlling)
Many operating and monitoring functions demand signals to be monitored and
messages to be displayed when they change. This functionality can be quickly and
easily realized with this software package.
In the configuration phase you determine which binary signals should be monitored
for change, whether it be inputs, outputs, memory bits or data bits. You can
configure up to 2048 signals, depending on the CPU. Each operand is assigned is
own message text. The CPU monitors the configured signals in a specific time
pattern (scan cycle). Each change to the configured signals is reported by the CPU
to the connected HMI device, which then displays the assigned message texts.
In addition to the change messages, the CPU can send up to ten values from the
CPU to the HMI station.
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Automation System S7-400 Configuration and Use
A5E00442711-02