INTRO to DIGITAL TECH

OR gate

Output is 1 only when one or both of its inputs are 1

Output is 1 only when both of its inputs are 1

Nand

Sequential Logic

A circuit producing outputs based on present and past inputs to store info (at least one bit).

Combinational Logic

Circuit output only dependent on present combinational input values

What are the two edges

Rising edge and falling edge

What does a rising and falling edge do?

Signals transitions between high and low state

What does a falling edge indicate?

A signal turning off, becoming false

What does a rising edge indicate?

A signal turning on, becoming true

Rising edge

Low to high state

Falling edge

High to low state

What happens in a clock flip flop?

The output only changes when there is an edge on the clock input

Edge triggered 1

output doesn’t change unless theres a specified edge signal

Edge triggered 2

Edge is rising or falling

Edge triggered 3

The input with a triangle symbol indicates the clock input

When the D clock’s active edge occurs

Q takes the value of D

When there is no activity in D clock edge

Q keeps previous value

TRUE OR FALSE: All digital sys with synchronous logic have a system clock

True

TRUE OR FALSE: Sys clocks usually produced by an oscillator is a regular square wave signal

True

Asynchronous Inputs

Change the output immediately to a set value, without waiting for the clock.

Negative edge trigger JK Flip flop

REVIEW

What are the two Asynchronous inputs called?

Preset and Clear

Preset input forces output to what value?

Q=1

What is the meaning of Q in flip flops?

The main output

Clear input forces output to what value?

Q=0

What is this?

Asynchronous table condictions REVIEW

What indicates that signals are active low

The circles on the inputs ( The 0 on the signal causes the set or reset to occur)

TRUE OR FALSE: No clock edge is necessary for the set or reset to take effect

TRUE

A negative edge-triggered D flip-flop responds to asynchronous timing signals like preset (PRE) and clear (CLR)

What is the difference between synchronous and asynchronous inputs?

Asynchronous changes the output immediately while
Synchronous changes the output only when the clock (or control signal) is active.

ACTIVE means

High or Low

MSI

One chip contained the combinational logic to handle data

MUX

take several input signals and send only one of them to the output.

What are the mux sizes

┌────────────┐

D ─▶│ │

CLK▶│► │

└─────Q──────┘

Synchronous

┌────────────┐

D ─▶│ │

CLK▶│► │

CLR▶│o │

└─────Q──────┘

Asynchronous

┌────────────┐

J ─▶│ │

K ─▶│ │

CLK▶│► │

└─────Q──────┘

Synchronous

┌────────────┐

D ─▶│ │

CLK▶│►o │

└─────Q──────┘

Falling edge

┌────────────┐

D ─▶│ │

CLK▶│► │

PR▶ │o │

└─────Q──────┘

Asynchronous

When does overflow occur

When ADDING 2 positives give a negative or 2 negatives give a positive

What indicates sign in sign bit system

1 = negative 0 = positive

A circuit that adds three bits and generates a sum and carry-out is know as a

Full adder

A circuit that adds two bits and generates a sum and carry-out is know as a

Half adder

When does overflow occur?

Results of binary addition and subtraction can’t be represented is too larger or small to fit in number of bits

Overflow in Binary addition

When you add two positive numbers but end up with a negative

Overflow in Binary subtraction

When you subtract two negative numbers but end up with a positive

If number being added has different signs

No overflow

If both numbers added have same signs

Overflow

If subtracted and signs are different its overflow because

The result has the same sign as the number being subtracted

Number being subtracted

Subtrahend