year 1 sequential logic

Question 1

what is combinational logic?

Answer 1

the output depends on the inputs only
it has no feedback

Question 2

what is sequential logic?

Answer 2

the output depends on the input and what the output was doing before
it has got feedback

Question 3

how does the not-set-not-reset work?

Answer 3

1. not-set goes low, Q goes high
2. not-set goes back high, Q stays low
3. not-reset goes low, Q goes low
4. not-reset goes back high, Q stays low

Question 4

what are some limitations of the not-set-not-reset?

Answer 4

inputs of 0 with 0 cause both outputs to be high
inputs are active low
outputs change straight away - not able to synchronise with other latches

Question 5

what is propagation delay?

Answer 5

logic gates take roughly 5ns for the signal to go through

Question 6

what is the purpose of a transition circuit?

Answer 6

a transition circuit provides a short pulse
if there are lots of latches synchronised on a clock pulse we add a transition circuit to ensure that the pulse is very short so the synchronisation is accurate

Question 7

how does the data latch work?

Answer 7

when the clock rises
what ever is at D
is sent to Q
and held there

Question 8

how do you wire a binary up ripple counter?

Answer 8

1. clock the first latch only
2. join not Q back to D
3. take outputs from Qs
4. not Q clocks the next latch
5. join all resets to 0v