lockup latches:
Lock-up latches are necessary to
avoid skew problems during shift phase of scan test. These problems occur if
FF’s driven by different clock lines are connected within a single scan chain.
eg: If you have a scan chain with
multiple clock domains in it the scan insertion tool should group registers
from the same clock domain. Then a lockup latch is used when going between the
two clock groups
A lockup latch is used to prevent
data corruption caused by overwriting of new data over the present data before
the clock edge occurs. i.e there is a potential problem of data coming early
and overwriting the present actual which has to be fed. This can be prevented
by placing a lock up latch with negative level sensitive D latch connecting the
two different chains. Especially used to avoid hold problems.
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