Design 4-Bit Synchronous Down Counter

Question

Problem: Design 4-Bit Synchronous Down Counter. Solve this hands-on electronics task on EWskills.

Accepted Answer

Connect all four T flip-flops to the same Clock so the counter operates synchronously. Use the complemented lower-order outputs to determine when each higher-order bit must toggle during down-counting.

T0 = 1
T1 = Q0'
T2 = Q1' · Q0'
T3 = Q2' · Q1' · Q0'

T0 remains HIGH, so Q0 toggles on every rising edge. Q1 toggles when Q0 = 0. Q2 toggles when Q1 and Q0 are both 0, while Q3 toggles when Q2, Q1, and Q0 are all 0. This produces the sequence from 1111 down to 0000 and then wraps back to 1111.

Use the active-low preset/reset connections to establish 1111 as the initial state. Connect Q3, Q2, Q1, and Q0 to Output_Buffer in MSB-to-LSB order.

Countdown timers and event counters.
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Frequency division and repeating 16-state timing sequences.

84. Design 4-Bit Synchronous Down Counter