Cooper LP800 Guia do Utilizador Página 447

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Critical Hazard 16
-7
This output (0-R-0) should be interpreted as a possible single
pulse, no longer than the duration of the R level. The actual
device’s output may or may not change, depending on the
transition times of the inputs.
Note that other types of primitives, such as flip-flops, may
produce an X instead of an R-0 or F-1 in response to a
convergence hazard.
Critical Hazard
It is important to note that the glitch so predicted could
propagate through the circuit and may cause incorrect operation.
If the glitch from a timing hazard becomes latched-up in an
internal state (such as flip-flop or ram), or if it causes an
incorrect state to be latched-up, it is called a critical hazard since
it definitely causes incorrect operation.
Otherwise, the hazard may pose no problem. Figure 16-7 shows
the same case as above, driving the data input to a latch.
Fi
g
ure 16-7
Critical Hazard Example
As long as the glitch always occurs well before the leading edge
of the clock input, it will not cause a problem.
QD
C
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