12-0 registers and counters © 2010. cengage learning, engineering. all rights reserved. 1-0 unit 12

12-1

Registers and Counters

© 2010. Cengage Learning, Engineering. All Rights Reserved.

1-1

UNIT UNIT 1212

12-2

Registers( 暫存器 ) 與 Counters( 計數器 ):

在一般的計算機中，暫存器被廣泛使用在記憶體以外的”暫時資料儲存”。因此對於 CPU等模組提供相互間的資料轉移、基礎運算。而計數器主要用來進行循序電路在處理工作上的排序，以時序脈波 (clock) 來控制信號。

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Figure 12.1 4-Bit D Flip-Flop Registers with Data, Load,

Clear, and Clock Inputs

4-Bits D-FF Register

1. This register has a load signal that ANDed the clock.2. When Load=0, register not clocked……hold the present value. when Load=1, the data will be load into the FF on the falling edge of the Clk3. For example, if Q outputs are (0000) and Data is (1101). when load=1, the output Q change to 1101 after falling edge clock. 4. However, this design with gating the Clk will lead to a timing problems.

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To avoid the timing issue, the signals are connected to become a common input

1.When Load =1, the Clk is enable, then D input will be loaded into the output Q2.With a bus notation.

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Figure 12.2 Data Transfer Between Registers

The Data transfer between Registers

When En=1, Load=1, the data in A will store in Q after the rising edge of the clock.When En=0, load=1, the data in B will store in Q.

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Figure 12.3 Logic Diagram for 8-Bit Register with Tri-State

Output

A 8-bit register and how data transfer by using tri-state bus

When EnA=0, A are output to bus, when LdG=1, data is load into register G

Use a decoder to select data transfer:

12-7

Figure 12.5 n-Bit Parallel Adder with Accumulator

A n-bits parallel adder with accumulator

To store one number(Xi) in a register of FF(called accumulator), and add a second Number(Yi) to it, leaving the results stored in the accumulator.

Process:1.ClrN2.Store Xi in Accumulator register (Ad, CLK) 3.Load adders input Yi, Si = Xi + Yi (Ad, CLK)

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Figure 12.6 Adder Cell with Multiplexer

Select Yi or Si into a register by a MUX : it is complex!!

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Figure 12.7 Right-Shift RegisterShift register

A shift register in which binary data can be stored and this data can be shifted to The left or right when shift signal is applied.

The initial register is 0101When Series input(1101) loadedThe sequence of the shift registerIs : 0101 1010 1101 0110 1011

Right-shift

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Figure 12.8 8-Bit Serial-in, Serial-out Shift Register

Shift registers: Serial-in Serial out:

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Figure 12.10 Parallel-in, Parallel-Out Right Shift Register

Shift registers: Parallel-in and Parallel-out

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Table 12.1 Shift Register Operation

Shift registers: Parallel-in and Parallel-out : two input control

0

1

1

0

1

0

1

0

©2010 Cengage Learning Engineering. All Rights Reserved. 12-13

Figure 12.12 Shift RegisterA shift register with inverted feed back is often called a Johnson counter

initial 000,D3= 1, then it become 100(and then 110,111,011….)

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Figure 12.13 Synchronous Binary Counter

Asynchronous Counter: 非同步二進制計數器又稱為漣波計數器 (Ripple counter)

1. 第一級的輸出狀態改變後，後一級才會有動作。2. 因此若連續加時脈信號到第一級 FF Clk, 則會進行一非同步的計數工作。3. N 個 FF 的非同步計數器，可以計數範圍由 0~2n-1 為止。舉例來說 , 下面可計數 0-15

J=K=1, 遇到負緣觸發 , 狀態反相

當 FF 的級數增加，而輸入時序脈波頻率很高，發生後一級正反器狀態還沒改變，下一時序脈波又再度送入第一級，導致計數錯誤。

這是非同步計數的缺點。

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Synchronous Counter: 同步二進制計數器

T-FF: 當 T=1, 轉態 (0 變 1, 1 變 0)

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Figure 12.14 Kanaugh Maps For Binary Counter

TA=1

Tc=BA TB=A


Figure 12.15 Binary Counter with D Flip-Flops

Synchronous Counter: 同步二進制計數器 : convert T-FF to a D-FFBy adding XOR gate.


Figure 12.16 Kanaugh Maps for D Flip-Flops

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Figure 12.17 State Graph and Table Up-Down Countre

UP-down binary counter

Up counter (U=1, D=0)

Down counter (U=0, D=1)


Figure 12.18 Binary Up-Down Counter


Figure 12.19 Loadable Counter with Count Enable


Figure 12.20 Circuit for Figure 12.19


Figure 12.21 State Graph for Counter


Table 12.3 State Table for Figure 12.21


Figure 12.22


Table 12.4 Input for T Flip-Flop


Figure 12.23 Counter Using T Flip-Flops


Figure 12.24 Timing Diagram for Figure 12.23


Figure 12.25 State Graph for Counter


Figure 12.26 Counter of Figure 12.21 Using D Flip-Flops


Table 12.5 S-R Flip-Flops Inputs


Table 12.6


Figure 12.27 Counter of Figure 12.21 Using S-R Flip-Flops


Table 12.7 J-K Flip-Flop Inputs


Table 12.8


Table 12.9 Determination of Flip-Flop Input


Figure 12.28 Counter of Figure 12.21 Using J-K Flip-Flops


Figure 12.29 Derivation of Flip-Flop Input


Images From End of Chapter Problems Problem 12.1

12-0 registers and counters © 2010. cengage learning, engineering. all rights reserved. 1-0 unit 12

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