Scan Chain Shift Cycle Trace
Design for Testability replaces standard flip-flops with scan flip-flops to allow direct observation and control of internal states during manufacturing tests. The schematic shows a 4-bit scan chain consisting of flip-flops FF3, FF2, FF1, and FF0 connected in series. The Scan_Enable signal is asserted high to place the circuit in shift mode. The Scan_In pin feeds directly into FF3, which cascades down to FF0.
Determine the exact sequence of bits that must be applied to Scan_In over four clock cycles to load the target test vector 1011 into [FF3, FF2, FF1, FF0].
Constraints
Scan_Enableis held at1for the duration of the shift operation.- The target state is represented as
[FF3, FF2, FF1, FF0] = 1, 0, 1, 1. - All flip-flops trigger on the rising edge of the clock.
Topics
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