One of more dual clock comparators (DCC) are
implemented as multi-purpose safety diagnostics. The DCC can be used to detect incorrect
frequencies and drift between clock sources. The DCC is composed of two counter blocks,
one is used as a reference time base and the second is used for the clock under test.
Both reference clock and clock under test may be selected via software, as can the
expected ratio of the clock frequencies. Deviation from the expected ratio generated an
error indication to the ESM. For more information on the clock selection options
implemented, refer to the device data sheet. For DCC programming details, refer the
device technical reference manual (TRM).
The DCC diagnostics is not enabled by default and must be
enabled via customer software. It is possible to disable and configure this diagnostic
via software. The cyclical check applied by the DCC module provides an inherent level of
self-checking (auto-coverage), which can be considered for application in latent fault
diagnostics.