BCD Counter: CO Timing Relative to Clock Edge
A synchronous cascaded BCD counter uses a combinational Carry Out (CO) from the ones stage to enable the tens stage.
Five signals are shown: CLK (clock, period 2), Q3 (ones counter bit 3), Q0 (ones counter bit 0), CO (combinational output), and Q0_tens (sequential output, initially 0). The combinational signal CO goes HIGH immediately whenever both Q3 and Q0 are HIGH. The sequential signal Q0_tens toggles its state on every LOW-to-HIGH transition of CLK if and only if CO is HIGH at that exact moment.
Trace CO and Q0_tens across all 12 time steps.
Constraints
COis strictly combinational and responds immediately to changes inQ3andQ0.Q0_tensis strictly sequential and evaluates the state ofCOonly at the exact moment of the rising clock edge.
Topics
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