Synchronous Counters
What are synchronous Counters? Synchronous counters are counters that eliminate the the Ripple Effect, all the flip flops are connected to the same external clock. The flip flops are layed out in a vertical format (compared to horizantal in asynchronous counters). The only downside to synchronous counters is that they require more logic.
Synchronous 3-Bit Binary-Up Counter with J/K Flip FlopsBelow is an sychronous 3-bit Binary-Up Counter using JK Flip Flops. As you can see all of the flip flops are connected to the same clock. This circuit is a divide by two circuit. So the output of the first flip flop pulses every count of the clock, the second flip flop pulses every two counts of the clock, and the third pulses every fourth count of the clock.
In the purple box is a switch that resets the clock to zero and stops it. |
Synchronous 3-Bit Binary-Down Counter with J/K Flip FlopsBelow is a down counter of the exact same counter to the left. The difference between these two, it that the and gate is no connected to Q' (Q not). This changes the polarity.
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Synchronous MOD-6 Binary UP counter
In this counter a three input NAND gate is used, the output of the NAND gate is connected to the CLR of each individual flip flop. The Switch is eliminated and now all three of the Q' (Qnots) must agree (all have an output 0) for it to clear. If they dont all agree than the ouput is a one so it doesn't clear.