SECTION 5-11 523) Use the Texas Instrument website to look up the 74ALS74A DFF.
ID: 2291239 • Letter: S
Question
SECTION 5-11 523) Use the Texas Instrument website to look up the 74ALS74A DFF. (a)* How long can it take for the Q output of a 74ALS74A to switch from 0 to 1 in response to an active CLK transition? (b)* How long does the D input need to be stable before the active clock edge on the 74ALS74A? (c) What is the narrowest pulse that can be applied to the PRE of a 74ALS74A FF? Use the Texas Instrument website to look up the 74ALS112A DFF. (a) How long does it typically take to asynchronously clear a 74ALS112? (b) How long maximum does it take to asynchronously set a 74ALS112? (c) What is the shortest acceptable interval between active clock transitions for a 74ALS74A? (d) The Jinput of a 74ALS112A goes HIGH 15 ns before the active clock edge. The K input has been at O. Will the flip-flop be reliably set? (e) How long does it take (after the clock edge) to synchronously store a 1 in a cleared 74ALS74A D flip-flop?Explanation / Answer
23.a. The corresponding parameter is tPLH mentioned in "switching characteristics" in page 4 in the datasheet
5ns < tPLH < 16ns
b. The corresponding parameter is tsu mentioned in "recommended operating conditions" in page 3 in the datasheet
tsu = 15ns
c. The corresponding parameter is tw mentioned in "recommended operating conditions" in page 4 in the datasheet
tw = 4ns.
24. a. tw for CLR is min 10ns. So it takes min of 10ns to asynchronously clear.
b. tw for PRE is min 10ns. So it takes min of 10ns to asynchronously set
c. The max frequency of operation is 30MHz which means the shortest interval between 2 active clock edges is is the time period = 1/fmax. ie Tmin = 1/(30e6) = 33.33ns.
d. The set up time tsu is 22ns. So the J input should appear at least 22ns before the active clock edge. So in this case since it appears only 15ns earlier, it is a setup violation and thus the flip flop wont be reliably set.
e. The parameter being referred here is the hold time th. As per the data sheet th is 0ns. So it takes 0ns or data is immediately stored after the clock edge.
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