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):
1

Why do we use truth tables?

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

2

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.

3

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

4

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

D is the input signal

is the output signal

Ck is the clock signal

5

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