Hello, my name is Totto.
One day during a training session, we were learning about flip-flops, and the terms synchronous counter and asynchronous counter came up.
I found myself thinking, ”Synchronous? Asynchronous? What's the difference?” I was confused.
I also learned from a senior colleague that "asynchronous circuits are not suitable for FPGA design" so I compared synchronous and asynchronous counters.
What are 'synchronous' and 'asynchronous'?
Synchronous and asynchronous are clock control methods.
･Synchronous: Registers run on the same clock.
･Asynchronous: Registers run on different clocks.
Schematics of synchronous and asynchronous counters
Figure 1 shows a synchronous counter with three registers connected to the same clock (red arrows).
Figure 1: Synchronous counter
The asynchronous counter in Figure 2 has the output of each register connected to the clock (yellow arrows).
Figure 2. Asynchronous Counter
Outputs of Synchronous and Asynchronous Counters
Figure 3 shows the register outputs of the synchronous counter and Figure 4 shows the register outputs of the asynchronous counter.
Figure 3: Three register outputs of the synchronous counter
Figure 4: Three register outputs for asynchronous counter
･ Synchronous counter : All bits change at the same time
･ Asynchronous counter : Each bit changes at a different time
Why do asynchronous counters not change all bits at the same time?
Theory Continued...
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