Successfully reported this slideshow.
Upcoming SlideShare
×

# Lect20 Engin112

See all

### Related Audiobooks

#### Free with a 30 day trial from Scribd

See all
• Full Name
Comment goes here.

Are you sure you want to Yes No
• Be the first to comment

### Lect20 Engin112

1. 1. ENGIN 112 Intro to Electrical and Computer Engineering Lecture 20 Sequential Circuits: Flip flopsENGIN112 L20: Sequential Circuits: Flip flops October 20, 2003
2. 2. Overvie w ° Latches respond to trigger levels on control inputs • Example: If G = 1, input reflected at output ° Difficult to precisely time when to store data with latches ° Flip flips store data on a rising or falling trigger edge. • Example: control input transitions from 0 -> 1, data input appears at output • Data remains stable in the flip flop until until next rising edge. ° Different types of flip flops serve different functions ° Flip flops can be defined with characteristic functions.ENGIN112 L20: Sequential Circuits: Flip flops October 20, 2003
3. 3. D Latch S D S’ Q C Q’ R R’ S R C Q Q’ D C Q Q’ 0 0 1 Q0 Q0’ Store 0 1 0 1 1 1 1 0 0 1 1 0 1 Reset X 0 Q0 Q0’ 1 0 1 1 0 Set 1 1 1 1 1 Disallowed X X 0 Q0 Q0’ Store ° When C is high, D passes from input to output (Q)ENGIN112 L20: Sequential Circuits: Flip flops October 20, 2003
4. 4. Clocking Event° What if the output only changed on a C transition? Positive edge triggered D C Q Q’ D Q 0 0 1 C Q’ 1 1 0 X 0 Q0 Q0’ Hi-Lo edge Lo-Hi edgeENGIN112 L20: Sequential Circuits: Flip flops October 20, 2003
5. 5. Master-Slave D Flip Flop ° Consider two latches combined together ° Only one C value active at a time ° Output changes on falling edge of the clockENGIN112 L20: Sequential Circuits: Flip flops October 20, 2003
6. 6. D Flip ° Stores a value on the positive edge of C - Flo ° Input changes at other times have no effect on output p Positive edge triggered D C Q Q’ D Q 0 0 1 C Q’ 1 1 0 X 0 Q0 Q0’ D gets latched to Q on the rising edge of the clock.ENGIN112 L20: Sequential Circuits: Flip flops October 20, 2003
7. 7. Clocked D Flip-Flop ° Stores a value on the positive edge of C ° Input changes at other times have no effect on outputENGIN112 L20: Sequential Circuits: Flip flops October 20, 2003
8. 8. Positive and Negative Edge D Flip- Flop ° D flops can be triggered on positive or negative edge ° Bubble before Clock (C) input indicates negative edge trigger Lo-Hi edge Hi-Lo edgeENGIN112 L20: Sequential Circuits: Flip flops October 20, 2003
9. 9. Positive Edge-Triggered J-K Flip-Flop °Created from D flop J K CLK Q Q’ °J sets 0 0 ↑ Q0 Q0’ 0 1 ↑ 0 1 °K resets 1 0 ↑ 1 0 °J=K=1 -> invert output 1 1 ↑ TOGGLEENGIN112 L20: Sequential Circuits: Flip flops October 20, 2003
10. 10. Clocked J-K Flip Flop ° Two data inputs, J and K ° J -> set, K -> reset, if J=K=1 then toggle output Characteristic TableENGIN112 L20: Sequential Circuits: Flip flops October 20, 2003
11. 11. Positive Edge-Triggered T Flip-Flop °Created from D flop T C Q Q’ °T=0 -> keep current 0 ↑ Q0 Q0’ °K resets TOGGLE 1 ↑ °T=1 -> invert currentENGIN112 L20: Sequential Circuits: Flip flops October 20, 2003
12. 12. Asynchronous Inputs• J, K are synchronous inputs o Effects on the output are synchronized with the CLK input.• Asynchronous inputs operate independently of the synchronousinputs and clock o Set the FF to 1/0 states at any time. ENGIN112 L20: Sequential Circuits: Flip flops October 20, 2003
13. 13. Asynchronous InputsENGIN112 L20: Sequential Circuits: Flip flops October 20, 2003
14. 14. Asynchronous Inputs • Note reset signal (R) for D flip flop • If R = 0, the output Q is cleared •This event can occur at any time, regardless of the value of the CLKENGIN112 L20: Sequential Circuits: Flip flops October 20, 2003
15. 15. Parallel Data Transfer ° Flip flops store outputs from combinational logic ° Multiple flops can store a collection of dataENGIN112 L20: Sequential Circuits: Flip flops October 20, 2003
16. 16. Summary ° Flip flops are powerful storage elements • They can be constructed from gates and latches! ° D flip flop is simplest and most widely used ° Asynchronous inputs allow for clearing and presetting the flip flop output ° Multiple flops allow for data storage • The basis of computer memory! ° Combine storage and logic to make a computation circuit ° Next time: Analyzing sequential circuits.ENGIN112 L20: Sequential Circuits: Flip flops October 20, 2003

### Be the first to comment

Dec. 8, 2015
• #### AashGates

Nov. 18, 2019

Total views

691

On Slideshare

0

From embeds

0

Number of embeds

12

19

Shares

0

0

Likes

2