1. REGISTERS AND COUNTERS
By Dr. Heman Pathak
Chapter -7

2. Registers
 A register is a group of flip-flops with each flip-flop capable of
storing one bit of information.
 An n-bit register has a group of n flip-flops and is capable of
storing any binary information of n bits.
 In addition to the flip-flops, a register may have combinational
gates that perform certain data-processing tasks.
 In its broadest definition, a register consists of a group of flip-flops
and gates that effect their transition.
 The flip-flops hold the binary information and the gates control when
and how new information is transferred into the register.

3. Registers

4. Loading the Register
 The transfer of new information into a register is
referred to as loading the register.
 Serial load: (transfer in serial mode)
 Transfer of new binary information into a register bit by bit
 Number of clock pulses needed to load the register =
 Number of flip-flops in the register
 Parallel load: (transfer in parallel mode)
 If all the bits of the register are loaded simultaneously with
a common clock pulse transition, we say that the loading is
done in parallel .

5. Registers with Parallel Load (RS Flip-flop)
S R Q(T+1)
0 0 Q(T)
0 1 0
1 0 1
1 1 -
L S R Q(T+1)
0 0 0 Q(T)
1 I I’ I
1 1 0 1
1 0 1 0
L
I
I’

7. Registers with Parallel Load (D Flip-flop)
D Q(T+1)
0 0
1 1
L d Q(T+1)
0 Q(T) Q(T)
1 I I
1 1 1
1 0 0
L’
Q
L
I
Q
I
L
D

9. Shift Registers
 A register capable of shifting its binary information in
one or both directions is called a shift register.

10. Shift Registers (Shift-Right)
1101 0 0 0 0
110 1 0 0 0
11 0 1 0 0
1 1 0 1 0
1 1 0 1
Serial load: (transfer in serial mode)
Transfer of new binary information into a register bit by bit
Number of clock pulses needed to load the register =
Number of flip-flops in the register

11. Shift Registers (Shift-Left)
0 0 0 0 1101
0 0 0 1 101
0 0 1 1 01
0 1 1 0 1
1 1 0 1

12. Shift Registers
 A register capable of shifting its binary information in one or both directions is
called a shift register.
 The logical configuration of a shift register consists of a chain of flip-flops in
cascade, with the output of one flip-flop connected to the input of the next flip-
flop.
 All flip-flops receive common clock pulses that initiate the shift from one stage to
the next.
 The simplest possible shift register is one that uses only flip-flops (D).
 The output of a given flip-flop is connected to the D input of the flip-flop at its
right.
 The clock is common to all flip-flops.
 The serial input determines what goes into the leftmost position during the shift.
 The serial output is taken from the output of the rightmost flip-flop.

13. Serial Transfer

14. Sequential Circuit

15. Sequential Circuit

16. Sequential Circuit

17. Bidirectional Shift Register with Parallel Load
 A register capable of shifting in one direction only is
called a unidirectional shift register.
 A register that can shift in both directions is called a
bidirectional shift register.
 Some shift registers provide the necessary input and
output terminals for parallel transfer.
 The most general shift register has all the capabilities
listed below.

18. Bidirectional Shift Register with Parallel Load
The most general shift register has all the capabilities listed
below.
1. An input for clock pulses to synchronize all operations.
2. A shift-right operation and a serial input line associated with the shift
right.
3. A shift-left operation and a serial input line associated with the shift-left.
4. A parallel load operation and n input lines associated with the parallel
5. transfer.
6. n parallel output lines.
7. A control state that leaves the information in the register unchanged
8. even though clock pulses are applied continuously.

19. Bidirectional Shift Register with Parallel Load
A4
No Change A4
Shift Right SIR
Shift Left A3
Parallel Load I4
A3
No Change A3
Shift Right A4
Shift Left A2
Parallel Load I3
A2
No Change A2
Shift Right A3
Shift Left A1
Parallel Load I2
A1
No Change A1
Shift Right A2
Shift Left SIL
Parallel Load I1
A4 A3 A2 A1

21. Serial Addition

22. Serial Addition

23. Serial Addition

24. Asynchronous or Ripple Counter
 Counter is a sequential circuit which is used for counting input
pulses passing through it.
 Counters are of two types.
 Asynchronous or ripple counters.
 Synchronous counters.
 A ripple counter is an asynchronous counter where only the first
flip-flop is clocked by an external clock.
 All subsequent flip-flops are clocked by the output of the
preceding flip-flop.
 Asynchronous counters are also called ripple-counters because of
the way the clock pulse ripples it way through the flip-flops.

25. Binary Ripple Counter
 Negative-Edge-Triggered J-K Flip-Flop

26. Binary Ripple Counter

27. Binary Ripple Counter

28. Binary Ripple Counter

29. Binary Ripple Counter

30. Binary Down Ripple Counter
Take the output from the
complemented terminals of
all flip-flops

31. Binary Down Ripple Counter
Instead of Negative-Edge-Triggered
flip-flops use Positive-Edge-Triggered
flip-flops

32. Binary Down Ripple Counter

33. BCD or Decade Ripple Counter
 BCD or Decade Ripple Counter is a serial digital counter that counts
ten digits.
 As it can go through 10 unique combinations of output, it is also
called as “Decade counter”.

34. BCD or Decade Ripple Counter
CLK Q8 Q4 Q2 Q1
Q1
CLK J K
External 1 1
Q2
CLK J K
Q1 Q8’ 1
Q4
CLK J K
Q2 1 1
Q8
CLK J K
Q1 Q2Q4 1

35. BCD or Decade Ripple Counter
Q8 Q4 Q2 Q1
Q1
CLK J K
External 1 1
Q2
CLK J K
Q1 Q8’ 1
Q4
CLK J K
Q2 1 1
Q8
CLK J K
Q1 Q2Q4 1

36. BCD or Decade Ripple Counter

37. BCD or Decade Ripple Counter

38. Synchronous Counter
 Synchronous Counters are so called because the
clock input of all the individual flip-flops within the
counter are all clocked together at the same time by
the same clock signal

39. Synchronous Down Counter
`
`
`
`

40. Synchronous Up-Down Counter
UP Down Action A4 A3 A2 A1
0 0 No Change 0 0 0 0
0 1 Down Counter A3’A2’A1’ A2’A1’ A1’ 1
1 0 Up Counter A3A2A1 A2A1 A1 1
1 1 Not Allowed - - - -

41. Synchronous Up-Down Counter

42. Synchronous BCD Counter

43. Synchronous BCD Counter
TQ2
8421 00 01 11 10
00 0 1 1 0
01 0 1 1 0
11 X X X X
10 0 0 X X
TQ4
8421 00 01 11 10
00 0 0 1 0
01 0 0 1 0
11 X X X X
10 0 0 X X
TQ8
8421 00 01 11 10
00 0 0 0 0
01 0 0 1 0
11 X X X X
10 0 1 X X

44. Binary Counter with Parallel Load
 Counter is basically a register that goes through a predetermined
sequence of state.
 This counter can be loaded in parallel with 4-Bit input data.
Load Count Action
0 0 No Change
0 1 Count
1 0 Load
1 1 Load
J K Action
0 0 No Change
Q Q Count
I I’ Load
I I’ Load

46. Binary Counter with Parallel Load

48. Timing Sequences in Serial Mode

49. Word-Time Generation

50. Timing Signals in Parallel Mode

51. Ring Counter
 A ring counter is a type of counter composed of flip-
flops connected into a shift register, with the output of the
last flip-flop fed to the input of the first, making a "circular"
or "ring" structure.

52. Ring Counter
Straight ring counter
Q0 Q1 Q2 Q3
0 1 0 0 0
1 0 1 0 0
2 0 0 1 0
3 0 0 0 1
0 1 0 0 0
1 0 1 0 0
2 0 0 1 0
3 0 0 0 1
0 1 0 0 0

53. Ring Counter

54. Ring Counter

55. Johnson Counter
 In Johnson counter, the complemented output of last flip
flop is connected to input of first flip flop.

56. Johnson Counter

57. Johnson Counter
Total number of used states = 2*n =2*4 = 8
Total number of unused states = 2n – 2*n = 24-2*4 = 8
 Advantages of Johnson counter:
 It can count twice the number of states the ring counter can count.
 Johnson ring counter is used to count the data in a continuous loop.
 Johnson counter is a self-decoding circuit.
 Disadvantages of Johnson counter:
 Johnson counter doesn’t count in a binary sequence.
 more number of states remain unutilized than the states being utilized.
 The number of flip flops needed is one half the number of timing signals.

58. Johnson Counter
A B C D
0 0 1 0
1 0 0 1
0 1 0 0
1 0 1 0
1 1 0 1
0 1 1 0
1 0 1 1
0 1 0 1

59. Integrated Circuits
 An integrated circuit (IC) is a small silicon
semiconductor crystal called a chip, containing
the electronic components for the digital gates.
 The various gates are interconnected inside the
chip to form the required circuit.
 The chip is mounted in a ceramic or plastic
container, and connections are welded by thin
gold wires to external pins to form the integrated
circuit.
 The number of pins may range from 14 in a small
IC package to 100 or more in a larger package.

60. Integrated Circuits
 As the technology of ICs has improved, the number of gates that can
be put in a single chip has increased considerably.
 Small-scale integration (SSI) devices contain several independent
gates in a single package. The inputs and outputs of the gates are
connected directly to the pins in the package. The number of gates is
usually less than 10 and is limited by the number of pins available in
the IC.
 Medium-scale integration (MSI) devices have a complexity of
approximately10 to 200 gates in a single package. They usually
perform specific elementary digital functions such as decoders,
adders, and registers.

61. Integrated Circuits
 LSI Large-scale integration (LSI) devices contain between 200 and a
few thousand gates in a single package. They include digital
systems, such as processors, memory chips, and programmable
modules.
 Very-large-scale integration (VLSI) devices contain thousands of gates
within a single package. Examples are large memory arrays and
complex microcomputer chips. Because of their small size and low
cost, VLSI devices have revolutionized the computer system design
technology, giving designers the capability to create structures that
previously were not economical.

62. Digital Logic Families
 Digital integrated circuits are classified not only by their logic operation
but also by the specific circuit technology to which they belong.
 The circuit technology is referred to as a digital logic family.
 Each logic family has its own basic electronic circuit upon which more
complex digital circuits and functions are developed.
 The basic circuit in each technology is either a NAND, a NOR, or an
inverter gate.
 The electronic components that are employed in the construction of the
basic circuit are usually used for the name of the technology.
 Many different logic families of integrated circuits have been introduced
commercially.

63. Digital Logic Families
 TTL - Transistor-transistor logic
 ECL - Emitter-coupled logic
 MOS - Metal-oxide semiconductor
 CMOS - Complementary metal-oxide semiconductor
 I2L - Integrated Injection Logic

64. Transistor-Transistor Logic
 TTL is a widespread logic family that has been in operation for many
years and is considered as standard.
 The transistor-transistor logic family was an evolution of a previous
technology that used diodes and transistors for the basic NAND gate.
 This technology was called DTL, for "diode-transistor logic." Later the
diodes were replaced by transistors to improve the circuit operation and
the name of the logic family was changed to "transistor-transistor logic."
 This is the reason for mentioning the word "transistor" twice.
 Power supply voltage for TTL circuits is 5 volts, and the two logic levels are
approximately 0 and 3.5 volts.

65. Transistor-Transistor Logic

66. Emitter-Coupled Logic (ECL)
 The emitter-coupled logic (ECL) family provides the
highest-speed digital circuits in integrated form.
 ECL is used in systems such as supercomputers and signal
processors where high speed is essential.
 The transistors in ECL gates operate in a non-saturated
state, a condition that allows the achievement of
propagation delays of 1 to 2 nanoseconds.

67. Emitter-Coupled Logic (ECL)

68. Metal-Oxide Semiconductor (MOS)
 The metal-oxide semiconductor (MOS) is a unipolar transistor that
depends on the flow of only one type of carrier, which may be
electrons (n-channel) or holes (p-channel).
 This is in contrast to the bipolar transistor used in TTL and ECL gates,
where both carriers exist during normal operation.
 A p-channel MOS is referred to as PMOS and an n-channel as
NMOS.
 NMOS is the one that is commonly used in circuits with only one type
of MOS transistor.

69. Complementary MOS (CMOS)
 The complementary MOS (CMOS) technology uses PMOS
and NMOS transistors connected in a complementary
fashion in all circuits.
 The most important advantages of CMOS over bipolar
are the high packing density of circuits, a simpler
processing technique during fabrication, and a more
economical operation because of low power consumption.

70. Complementary MOS (CMOS)

71. INTEGRATED INJECTION LOGIC
 Integrated injection logic (IIL, I2L, or I2L) is a class of digital circuits built with
multiple collector bipolar junction transistors (BJT).
 When introduced it had speed comparable to TTL yet was almost as low power as
CMOS, making it ideal for use in VLSI (and larger) integrated circuits.
 The gates can be made smaller with this logic family than with CMOS because
complementary transistors are not needed.
 Although the logic voltage levels are very close (High: 0.7V, Low: 0.2V), I2L has
high noise immunity because it operates by current instead of voltage.
 I2L was developed in 1971 by Siegfried K. Wiedmann and Horst H. Berger who
originally called it merged-transistor logic (MTL).
 A disadvantage of this logic family is that the gates draw power when not
switching unlike with CMOS.