Electrical Engineering Question: Download Questions PDF
Given the following FIFO and rules, how deep does the FIFO need to be to prevent underflowing or overflowing?
Answer:
Given the following FIFO and rules, how deep does the FIFO need to be to prevent underflowing or overflowing?
RULES:
1) frequency(clk_A) = frequency(clk_B) / 4
2) period(en_B) = period(clk_A) * 100
3) duty_cycle(en_B) = 25%
Assume clk_B = 100MHz (10ns)
From (1), clk_A = 25MHz (40ns)
From (2), period(en_B) = 40ns * 400 = 4000ns, but we only output for 1000ns, due to (3), so 3000ns of the enable we are doing no output work.
Therefore, FIFO size = 3000ns/40ns = 75 entries.
RULES:
1) frequency(clk_A) = frequency(clk_B) / 4
2) period(en_B) = period(clk_A) * 100
3) duty_cycle(en_B) = 25%
Assume clk_B = 100MHz (10ns)
From (1), clk_A = 25MHz (40ns)
From (2), period(en_B) = 40ns * 400 = 4000ns, but we only output for 1000ns, due to (3), so 3000ns of the enable we are doing no output work.
Therefore, FIFO size = 3000ns/40ns = 75 entries.
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