CPU Operation 77
Section 4: CPU Operation
This Section describes the operating modes of a PACSystems CPU and describes the tasks
the CPU carries out during these modes. The following topics are discussed:
▪ CPU Sweep
▪ Program Scheduling Modes
▪ Window Modes
▪ Data Coherency in Communications Windows
▪ Run/Stop Operations
▪ Flash Memory Operation
▪ RUN/STOP Switch Operation
▪ The RUN/STOP Switch is a 3-position switch which operates as follows:
RUN I/O or
RUN I/O Enable
The CPU runs with I/O sweep enabled.
User program memory is read only.
RUN or
RUN Output
Disable
The CPU runs with outputs disabled.
User program memory is read only.
The CPU is not allowed to go into RUN
Mode.
User program memory can be
written.
The RUN/STOP Switch can be disabled in the programming software HWC. The memory
protection function of the switch can be disabled separately in HWC. The RUN/STOP
Switch is enabled by default. The memory protection functionality is disabled by default.
The Read Switch Position (Switch_Pos) function allows the logic to read the current
position of the RUN/STOP Switch, as well as the mode for which the switch is configured.
For details, refer to PACSystems RX3i and RSTi-EP CPU Programmer’s Reference Manual, GFK-
2950.
▪ Logic/Configuration Source and CPU Operating Mode at Power-Up
▪ System Security
▪ PACSystems I/O System
▪ Power-Up and Power-Down Sequences
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