Truth Tables and the Clock Flashcards Preview

Digital System Design 2 > Truth Tables and the Clock > Flashcards

Flashcards in Truth Tables and the Clock Deck (5):

Why do we use truth tables?

To encode behaviour, by noting how each input codeword maps to each output codeword


Why do we use the clock signal?

To create a sequence of operations (in RTL) we need time to structure it. Circuit imperfections such as propogation delay and rising/falling times are managed and hidden behind a logical delay, which we create using the alternating high/low clock signal. Each consecutive high/low pair is a clock cycle.


Describe the difference between combinational and sequential gates.

Combinational gates perform logic value operations and have variable delay 

Sequential gates perform logic value storage and require very particular delay values


Describe the D flip-flop, giving its 3 principle signals

D is the input signal

is the output signal

Ck is the clock signal


Where are the following delays measured from?

Propagation delay tpd?

Set up time tsu?

Hold time th?

tpd = Clock to Q

tsu = Clock back to D

th = Clock forward to D