Dept. of Applied Electronics Technology, NTNU

6.06.0Registers and CountersRegisters and Counters

, Jeng-Han Tsaijht i@ t d tjhtsai@ntnu.edu.tw

http://web.ntnu.edu.tw/~jhtsai/

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Dept. of Applied Electronics Technology, NTNU

6-1 Registers6-1 RegistersA n-bit register

n flip-flops capable of storing n bits of binary information4-bit register

Fig. 6.1

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Fig. 6.1Four-bit register

Dept. of Applied Electronics Technology, NTNU

4-bit register with parallel loadg pload'

load

Fig 6 2Fig. 6.2Four-bit register with parallel

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with parallel load

Dept. of Applied Electronics Technology, NTNU

6-2 Shift Registers6-2 Shift RegistersShift register

a register capable of shifting its binary information in one or both directions

Simplest shift register

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01 10

11

01

Fig. 6.3

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Fig. 6.3Four-bit shift register

Dept. of Applied Electronics Technology, NTNU

Serial transfer vs. Parallel transferSerial transfer

Information is transferred one bit at a timeshifts the bits out of the source register into the destination register

Parallel transfer:All the bits of the register are transferred at the same time

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Dept. of Applied Electronics Technology, NTNU

Example: Serial transfer from reg A to reg Bp g g

Fig. 6.4

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gSerial transfer from register A to register B

Dept. of Applied Electronics Technology, NTNU

Example: Serial transfer from reg A to reg BExample: Serial transfer from reg A to reg B

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Dept. of Applied Electronics Technology, NTNU

Serial addition using D flip-flopsSerial addition using D flip flops

01011 0

101000

1 01

1010

11

10011?001

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Fig. 6.5Serial adder

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Serial adder

Dept. of Applied Electronics Technology, NTNU

Serial adder using JK flip-flopsg p p

JQ = x yK ( )

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KQ = x y = (x + y)S = x y Q

Dept. of Applied Electronics Technology, NTNU

Circuit diagramJQ = x yKQ = x y = (x + y)S QS = x y Q

CiCi

Fi 6 6

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Fig. 6.6Second form of serial adder

Dept. of Applied Electronics Technology, NTNU

Universal Shift RegisterUnidirectional shift registerBidirectional shift registerBidirectional shift registerUniversal shift register:

has both direction shifts & parallel load/out capabilitieshas both direction shifts & parallel load/out capabilities

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Dept. of Applied Electronics Technology, NTNU

Capability of a universal shift register:1 A l t l t l th i t t 01. A clear control to clear the register to 0.2. A clock input to synchronize the operations.3 A shift right control to enable the shift right operation and3. A shift-right control to enable the shift right operation and

the serial input and output lines associated w/ the shift right.4. A shift-left control to enable the shift left operation and the f f p

serial input and output lines associated w/ the shift left.5. A parallel-load control to enable a parallel transfer and the n

ll l i li i d / h ll l fparallel input lines associated w/ the parallel transfer.6. n parallel output lines.7 A control state that leaves the information in the register7. A control state that leaves the information in the register

unchanged in the presence of the clock.

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Dept. of Applied Electronics Technology, NTNU

Example: 4-bit universal shift registerExample: 4 bit universal shift register

Fig 6 7

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Fig. 6.7Four-bit universal shift register

Dept. of Applied Electronics Technology, NTNU

Function table !

Clear s1 s0 A3+ A2+ A1+ A0+ (operation)C ea s1 s0 3 2 1 0 (ope at o )

0 0 0 0 0 Clear1 0 0 A A A A N h e1 0 0 A3 A2 A1 A0 No change1 0 1 sri A3 A2 A1 Shift right1 1 0 A A A sli Shift left1 1 0 A2 A1 A0 sli Shift left1 1 1 I3 I2 I1 I0 Parallel load

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Dept. of Applied Electronics Technology, NTNU

Function Table Function Table

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Dept. of Applied Electronics Technology, NTNU

AA A1A2

A0

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Fig. 6.7 Four-bit universal shift register (continued)

Dept. of Applied Electronics Technology, NTNU

6-3 Ripple Counters6-3 Ripple CountersCounter:

a register that goes through a prescribed sequence of statesupon the application of input pulses

Input pulses: may be clock pulses or originate from some external source

The sequence of states: may follow the binary number sequence ( Binary counter) orthe binary number sequence ( Binary counter) orany other sequence of states

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Dept. of Applied Electronics Technology, NTNU

Categories of counters1.Ripple counters

The flip-flop output transition serves as a source for triggering other flip-flops

no common clock pulse (not synchronous)

2 S h t2.Synchronous counters:The CLK inputs of all flip-flops receive a common clock

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Dept. of Applied Electronics Technology, NTNU

Example: 4-bit binary ripple counter Binary count sequence: 4-bit

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Dept. of Applied Electronics Technology, NTNU

10

10

Fig. 6.8 Four-bit binary ripple

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y ppcounter

Dept. of Applied Electronics Technology, NTNU

BCD ripple counterBCD ripple counter

Fig. 6.9 State diagram of a decimal BCD counter

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g

Dept. of Applied Electronics Technology, NTNU

The circuitThe circuit

Fig. 6.10 BCD ripple counter

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pp

Dept. of Applied Electronics Technology, NTNU

Three-decade BCD counterThree-decade BCD counter

Fig. 6.11 Block diagram of a three decade decimal BCD counterBlock diagram of a three-decade decimal BCD counter

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Dept. of Applied Electronics Technology, NTNU

6-4 Synchronous Counters6-4 Synchronous CountersSync counter

A common clock triggers all flip-flops simultaneously

Design procedureapply the same procedure of sync seq cktspp y p y qSync counter is simpler than general sync seq ckts

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Dept. of Applied Electronics Technology, NTNU

4-bit binary countery

C_en A0_ 0

C_en A0 A1

C_en A0 A1 A2

Fig. 6.12 Four-bit synchronous binary counter

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y y

Dept. of Applied Electronics Technology, NTNU

4-bit up/down up

pbinary counter down up A0

down A'0

down A'0 A'1 up A0 A1

down A'0 A'1 A'2

Fig 6 13

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Fig. 6.13 Four-bit up-down binary counter

Dept. of Applied Electronics Technology, NTNU

BCD countersBCD counters

Si lifi d f i Simplified functions:

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Dept. of Applied Electronics Technology, NTNU

282010/12