Rockwell Automation Chassis Models - Manual (Page 2)

2 Chassis Models October 2005 – Issue 4
Triguard SC300E
Figure 1-1. SC300E Architecture
As c an be seen from the block diagram in Figure 1-1 a SC300E system has a fully triplicated
architecture from input modules to output modules. All SC300E input and output modules
interface to three isolated I/O communications buses, each being controlled by one of the three
main processor modules.
At the input modules, field signals are filtered and then split, via isolating circuitry, into three
identical, signal processing paths. Each path is controlled by a microcontroller that co-
ordinates signal path processing, testing and signal status reporting to its respective main
processor, via one of the I/O communications buses.
Each of the main processors communicates with its neighbours via read only, serial
communications links. The main processors synchronise at least once per application logic
execution cycle, and each reads the input, output and diagnostic status of its neighbours.
Each processor correlates and corrects its memory image of the current state of the system
using a 2-oo-3 software vote, logging any discrepancies found in a local diagnostic history
table.
Each processor then executes its programmed application logic and sets its respective
outputs, via the I/O communications bus, to the required state.
Commanded output states are received by an output module’s microcontrollers which, using 2-
oo-3 hardware voters, set the outputs to the field. Any discrepancy between a commanded
output state and the field output is detected by the microcontrollers and reported to the
appropriate main processor.