Logic Lab
Counters
3-bit T counter, ripple, BCD, synchronous and up/down counters, with timing waves, state tables and state diagrams.
3-bit (T flip-flops)
Count0
Binary Q2…Q0000
Modulus8
FF2 Q=0T2 = 0
FF1 Q=0T1 = 0
FF0 Q=0T0 = 1
Built from flip-flops and logic gates
The boxes are flip-flops; the gates between them decide when each one toggles. The wires carry the live values, so pulse the clock and watch the T inputs change.
CLK
Q0
Q1
Q2
State table
| Present | Next | T2 T1 T0 |
|---|---|---|
| 000 | 001 | 0 0 1 |
| 001 | 010 | 0 1 1 |
| 010 | 011 | 0 0 1 |
| 011 | 100 | 1 1 1 |
| 100 | 101 | 0 0 1 |
| 101 | 110 | 0 1 1 |
| 110 | 111 | 0 0 1 |
| 111 | 000 | 1 1 1 |
State diagram
Three T flip-flops on one clock. T0 = 1, T1 = Q0, T2 = Q0·Q1: a flip-flop toggles exactly when every lower bit is 1, which is how binary counting carries. The highlighted row is the current state. A T flip-flop toggles when its T input is 1, so the T columns are the design: they are read straight off the state table.