11/27/2023 0 Comments Scannable ghost 32Note that this means the gate driving the data input D must be strong enough to overpower the feedback inverter. The small inverters represent weak feedback devices they must be ratioed to allow proper writing of the cell. While it is possible to use a single scan clock, the two-phase nonoverlapping scan clocks shown are more robust and simplify clock routing. The contents of latch can be scanned out to SDO (scan data out) and loaded from SDI (scan data in) by toggling the scan clocks SCA and SCB. The circuits shown in the dashed boxes are added to the basic latch for scan. When the clock is stopped low, the latch is opaque. Normal latch operation involves input D, output Q, and clock ϕ. Systems built from transparent latches or pulsed latches can be made observable and controllable by adding scan circuitry to every cycle of logic.
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