Definitions

Definitions

• Definitions

• Latches

• Set-Reset – SR
• The D Latch

• Material from section 5-3 of text

When the control input to a flip-flop changes value the state of the latch in the flip-flop will change state.

• When the control input to a flip-flop changes value the state of the latch in the flip-flop will change state.

• In a D-latch when the control input is a ‘1’, any changes on the input D will propagate to the output with the value of D at the time the control transitions from ‘1’ the final stored value.

• In a D flip-flop, the value on D on the rising edge (falling edge) of the control input will be the captured value.

Constructed in such a way that they are edge-triggered.

• Constructed in such a way that they are edge-triggered.

• This is in contrast to latches which are level sensitive and said to be transparent.

• There are two general methodologies for making flip-flops

• Edge-triggered
• Master-Slave

The Master-Slave SR Flip-flop

• The Master-Slave SR Flip-flop

• And its operation

Can be constructed from the MS SR FF by replacing the master SR latch by a D latch.

• Can be constructed from the MS SR FF by replacing the master SR latch by a D latch.

• This arrangement is also negative edge triggered.

The SR latch model with control input C

• The SR latch model with control input C

tb model

• tb model

• Links in the latch in a master slave manner

Waveform display

• Waveform display

The D can be constructed from the use of a D latch and an SR latch.

• The D can be constructed from the use of a D latch and an SR latch.

Add an inverter to the clock input

• Add an inverter to the clock input

A HDL model of the D latch was written.

• A HDL model of the D latch was written.

Results now for the D F/F

• Results now for the D F/F

• Remember the delays

Allows direct setting of state of flip-flop.

• Allows direct setting of state of flip-flop.

• When initially powered state of flip-flop is unknown. The sets the FF to a known state.

Covered sections 5-1 and 5-2

• Covered sections 5-1 and 5-2

• Problems for hand in

• L20 HW (on webpage)

• Problems for practice

• none

• Reading for next class: sections 5-4