3.1.2 Functional Duplication

More advanced systems can have both local safety supervisor processors and network-level safety supervisors. The local safety supervisor is expected to execute application-level diagnostics and relay the status up to the network safety supervisor through the available communication channels.

The following figure shows a simplified ASIL D system that includes the two levels of safety supervisors. For added reliability, duplication of device output clocks, communication channels (via PIC18F1220/1320s MCUs), switches, and SoCs has been applied. By these means, any failures in one clock/switch/SoC can be communicated to the local supervisor who can switch the parallel system in and advise the network supervisor.