A FIFO written and read on separate clocks, used to pass multi-bit data between clock domains. Its pointers are converted to Gray code before being synchronized into the other domain to decide full and empty. The pointers have one more bit than the address to distinguish wrap-around.
Japanese name: 非同期FIFO
Asynchronous FIFO appears in 10 practice questions across 1 topic, including Timing analysis and CDC.
Field: Timing analysis and CDC
Answer: B. Because only one bit changes per increment, so even if captured mid-change the result is the correct value from before or after the increment
A binary pointer can change multiple bits at once, as in 0111 to 1000, so synchronizing each bit separately can yield a completely unrelated value. With Gray code only one bit changes per increment, so even if that bit goes metastable and resolves to either the old or new value, the result is the value from before or after the increment. The receiver merely sees a slightly stale value, so the FIFO does not break. The number of bits does not change, and metastability itself can still occur, so synchronizers are still required.
Answer: B. So that when the pointers match, empty (same lap) can be distinguished from full (one lap apart)
The addresses of 16 words fit in 4 bits, but with 4-bit pointers alone, when the read and write addresses match it is impossible to tell whether the FIFO is empty because everything has been read, or full because writing has gone a full lap and caught up. Adding a fifth bit that indicates the lap means that, comparing in binary, the FIFO is empty when all 5 bits match and full when only the MSB differs. With Gray code pointers, the comparison for full is slightly different. The bit is not used as parity.
For counter values, convert to Gray code so that only one bit changes; for arbitrary data, use a handshake or an asynchronous FIFO.
Each bit of 4-bit data is passed to another clock domain th…For continuous high-volume transfer, use an asynchronous FIFO.
Which is a correct way to pass multi-bit data safely to ano…When the spacing cannot be guaranteed, use a handshake that waits for the receiver's response, or an asynchronous FIFO.
What constraint applies when passing pulses from a fast clo…For streaming data almost every cycle, use an asynchronous FIFO.
Which is a drawback of transferring data between clock doma…As an Amazon Associate I earn from qualifying purchases.
Gray code Clock domain Handshake Metastability Synchronizer Yield False path Place and route Clock uncertainty Critical path