Rockwell Automation T71xx Regent+Plus Processor Modules 110 VAC, 220/240VAC and 24VDC - Manual (Page 3)

Processor Modules (T7110, 11, 12, 20, 21, and 22)
P D - 7 0 0 0 S e p - 0 4 (Issue 1)
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one processor module — allowing the other two modules to
continue operating — thus keeping the Regent on-line by virtue of
its majority two-out-of-three voting architecture.
Programs are stored in on-board battery-backed RAM. Program
instructions are fetched from each processor’s memory and
executed by the processors. Data from inputs are read from the
I/O modules in the I/O assembly. The main processor coordinates
the Regent’s activities and solves the application algorithms
programmed by the user. Outputs are driven by transmitting data
through the processor module’s I/O processor to the I/O assembly.
Communications between the main processor and the I/O
processor are maintained through shared RAM that is used as a
“mail box” for data transfers between the two processors.
All three processor modules operate independently in lock-step
synchronization with the other two modules, continuously
repeating a scan cycle (Figure 2).
Figure 2. The Regent’s Scan Cycle.
The main processors in each of the three processor modules run
programs and process communications synchronously, while the
I/O processors in each module read and write I/O synchronously.
During these synchronous operations, all instructions and data are
distributed across the Safetybus where automatic voting and fault
detection occur.
Main Processor
During each scan cycle, the main processor executes application
programs, reading inputs from the shared RAM and writing
outputs to the shared RAM.