Flip Flops

1
Flip Flops

• TI Type 502 Flip Flop 1st production IC in 1960.

2
Interest

• 1919 W. H. Eccles and F. W. Jordan publish the
  first flip-flop circuit design.
• M74HC74AM Fairchild CMOS flip-flop for frequency
  manipulation is used in a Smart Card Reader.

3
Logic Circuit Classifications

• Combination Logic Circuits
• Building block is the logic gate.
• Use AND, OR, NOT gates.
• Sequential Logic Circuits
• Building block is the flip flop (FF).
• Used in timing and memory devices.
• Flip Flops are wired to form counters, shift
  registers, and various memory devices.

4
R-S Flip Flop

• Logic Symbol Wiring
  Diagram

Also called R-S Latch Set-Reset FF
Set
Normal
Output
Input
Reset
Complementary

• Truth Table
  Waveform Diagram

Set
Hold
Reset
Set
Hold
Input
S
R
Q
Output
5
Clocked R-S Flip Flop

• Logic Symbol Wiring
  Diagram

Output FF operates Synchronously in step with
clock.

• Truth Table
  Waveform Diagram

CLK
Input
S
R
Q
Output
6
Questions

• Q. What type of waveform is used in flip flops?
• A. Square Waves.
• Q. What does the RS stand for in the RS Flip
  Flop?
• A. Reset Set.

7
D Flip Flop

• Logic Symbol Wiring
  Diagram

Also called Delay FF Data FF D-type
Latches Delayed 1 Clock Pulse
Data
Normal
D
Q
Output
Input
FF
Clock
Complementary
CLK

• Truth Table
  Similar Wiring

FF
D
Q
S
Q

CLK
FF
CLK
R
8
7474 D Flip Flop

• Logic Symbol

Note The asynchronous inputs (PS CLR) Override
the synchronous inputs (D CLK) .
Data
Normal
PS
D
Q
Output
Input
FF
Clock
Complementary
CLK

• Truth Table

9
D (Delay) Flip Flop Uses

• Sequential logic devices used in temporary memory
  devices.
• Wired together to form shift registers and
  storage registers.
• Delays data from reaching output Q one clock
  pulse.
• CMOS examples 74HC74, 74FCT374, 40174
• Over 50 different ICs in FACT CMOS family.

10
J-K Flip Flop

• Logic Symbol

• Truth Table

11
7476 J-K Flip Flop

• Logic Symbol

Note 7476 uses the entire pulse to transfer data
from J K data inputs to Q Q outputs.

• Truth Table

12
J-K Flip Flop Uses

• Universal Flip Flop. Has all features of other
  FF.
• When being used only in the toggle mode, commonly
  called a T Flip Flop.
• CMOS examples 74HC76, 74AC109, 4027.
• Most commonly used as counters.

13
Questions

• Q. What circuit can be used to give a clock
  signal?
• A. Astable multivibrater.

14
IC Latches

• Input
• Keyboard

Output Display
Encoder
4-Bit Latch
Decoder
7
8
9
4
5
6
1
2
3
0
Decimal
Decimal
Binary

• A device that serves as a temporary buffer memory
  is called a latch. An example of a 4-bit latch is
  the 7475.
• A latch is transparent when the enable input is
  high, the normal outputs follow the data in the D
  inputs.
• One example of flip flops is to latch or hold
  data.

15
IC Latch Uses

• The latch is the fundamental memory device used
  in digital electronics.
• Almost all digital equipment contains simple
  memory devices called latches.
• CMOS examples 4042, 4099, 74HC75
• 4043 is an example of a BCD-7 Segment
  latch/decoder/driver chip.

16
CMOS D Flip-Flop Schematic
17
D Flip Flop using Nor gates
What logic gates are more efficient?
18
CMOS D Flip-Flop

• CMOS technology allows a very different approach
  to flip-flop design and construction. Instead of
  using logic gates to connect the clock signal to
  the master and slave sections of the flip-flop, a
  CMOS flip-flop uses transmission gates to control
  the data connections.

19
Triggering Flip Flops

• The added inverter bubble at the clock input
  shows that triggering occurs on the negative
  going edge of the clock pulse.
• The J-K master/slave flip flop uses the entire
  pulse (positive edge and the negative edge) to
  trigger the flip flop.
• Waveform 165.

20
Schmidt Trigger

• Schmidt Trigger Inverter commonly used to square
  up input signal. This reshaping of the waveform
  is called signal conditioning.

21
IEEE vs. Logical Symbols

• See internet links.

22
Conclusions

• Q. What are some circuit uses for flip flops?
• A. Counters, shift registers, and various memory
  devices.