HDL & Verification
What is the difference between synchronous and asynchronous resets?
- AA synchronous reset acts regardless of the clock; an asynchronous one only at clock edges
- BA synchronous reset takes effect only at clock edges; an asynchronous reset takes effect immediately regardless of the clock
- CThey behave identically; only the names differ
Show answer and explanation
Answer: B. A synchronous reset takes effect only at clock edges; an asynchronous reset takes effect immediately regardless of the clock
A synchronous reset samples the reset signal at clock edges like any other input, which eases timing analysis, but it cannot reset without a running clock. An asynchronous reset uses the flip-flop's reset pin directly, so it acts at once even without a clock, but if release happens near a clock edge, flip-flops may come out of reset at different cycles.
- A. It is the other way around.
- B. Correct. Each has advantages and caveats.
- C. They differ in when the reset takes effect.