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电子科技大学2014 - 2015 学年第 二 学期期 中 考试卷

课程名称：数字逻辑设计及应用 考试形式：闭卷 考试日期：2015年5月10日 考试时长：120分钟

课程成绩构成：平时 30/20 %， 期中 30/20 %， 小班讨论 0/20 %， 期末 40 % 本试卷试题由__VII___部分构成，共__6___页。

题号 得分 得 分 I. Please fill out the correct answers in the brackets “( )” . ( 2’ X 20 = 40’ )

1. [510.5] 10 = ( 111111110.1 )2 = ( 1FE.8 ) 16

2. (2015)10 =( 0010000000010101 )8421BCD =( 0101001101001000 ) Excess-3

3. If X’s signed-magnitude representation XSM is 000110102, then (2X)’s 8-bit two’s

complement representation is ( 00110100 ), and (-X/2)’s 8-bit two’s complement representation is ( 11110011 ). 4. If a logic function is

(0,4,5,7),

is

.(0,2,3,7)

and

, its complement expression is

its

dual

expression

I II III IV V VI VII 合计 5. For CMOS inverters, can different outputs of common CMOS inverters be connected together?

[Yes or No] ( No ); Three-state inverters have three-state outputs, which are HIGH、LOW and ( Hi-Z ). Can different outputs of three-state inverters be connected together? [Yes or No] ( Yes ). 6. Given a binary number X=101101012, its corresponding Gray code is ( 11101111 ).

7. If [X] two’s-complement =0111 00112, [Y] two’s-complement =1001 11002, then [X-Y] two’s-complement=（ 10101001 ），whether overflow occurs? [Yes or No] ( Yes ). 8. Given 126 different states, it requires at least (

7 ) binary bits to represent them.

9. For CMOS NOR gates, their unused inputs should connect to ( 0 ) state. 10. From Table 1 below, if 74HC devices drive 74LS devices,

in HIGH state , DC noise margin VNH is ( 1.84 ), Fan-out NH is ( 200 ); in LOW state , DC noise margin VNL is ( 0.47 ), Fan-out NL is ( 10 ).

Table 1

Description

LOW-level input voltage (V) LOW-level output voltage (V) HIGH-level input voltage (V) HIGH-level output voltage (V) LOW-level input current (uA) LOW-level output current (mA) HIGH-level input current (uA) HIGH-level output current (mA)

Symbol VILmax VOLmax VIHmin VOHmin IILmax IOLmax IIHmax IOHmax

Family 74LS 0.8 0.5 2.0 2.7 -400 8 20 -0.4

74HC 1.35 0.33 3.85 3.84 1 4 -1 -4

得 分

II. Choose the correct answer and fill the item number in the brackets. (Single

selection for question 1~8, Multi-selection for 9~10, 2’ X 10=20 ) 1. For logic function

( C ) A. C.

B.

D.

, its minimal sum is

2. Given a circuit design, its output expression with positive logic is

then its output expression with negative logic is ( A.

B.

C

)

,

C. D.

3. For the priority encoder 74X148, its inputs are: I0-L, I1-L, I2-L, I3-L, I4-L, I5-L, I6-L, I7-L，outputs are Y2-L,Y1-L,Y0-L. The inputs and outputs are all active-low. When active-low enable input EN_L=0, I1-L = I5-L = I4-L =0, and any other inputs are all 1, then Y2-L, Y1-L, Y0-L is

( B ).

A. 110 B. 010 C. 001 4. Except enable lines, an 8-1 multiplexer should have ( A. 1 B. 2 C. 3

D. 101

C ) control/select lines. D. 4

5. The truth table of a circuit is shown in Table 2, the logic expression of this circuit is ( D ).

A. F=A+B B. F=S+A+B C.

Table 2 S 0 0 0 0 1 1 1 1 6. In one number system

B ) A. 5

B. 6

C. 7

B

B) D)

D. 8 )

A 0 0 1 1 0 0 1 1 B 0 1 0 1 0 1 0 1 F 0 1 0 1 0 0 1 1 is correct, its radix is ( D.

7. In figure 1, the output logic function is (

A) C)

ABCDEFigure 1

VccY

8. If the minimal sum of a logic function is same as canonical sum, it may have ( A. static-0 hazard

B. static-1 hazard

D ).

C. both static-0 hazard and static-1 hazard D. neither static-0 hazard nor static-1 hazard 9. In two-level AND-OR circuit design, our minimization is aimed to (

B

C

)

A. minimize the inputs of OR gates B. minimize the number of AND gates

C. minimize the inputs of AND gates D. shorten the signal path from input to output 10. Methods that are ( A A. sum-of-products C. truth table

B

C

D

) can be used to describe combinational circuits

B. product-of-sums D. timing diagram

III. Combinational Circuit Analysis And Design: [40’] 1.Given F(W,X,Y,Z)=W/Y/Z/+W/X/Z+WXY/Z+YZ, there are also don’t-cares defined as d(9,12,14). Simplify the logic function F(A,B,C,D) into the minimal-product using Karnaugh map, and write out NOR-NOR logic expression of the minimal-product. (8’)

参考评分标准：

1.填写F的卡诺图正确4分 2.化简的表达式正确2分

Fminimal-product (W,X,Y,Z)=(Y/+Z)(W/+Z)(W+X/+Y+Z/)

3.“或非-或非“表达式正确2分

FNOR-NOR(W,X,Y,Z) = [(Y/+Z)/+(W/+Z)/+(W+X/+Y+Z/)/]/

2. A combinational circuit is shown as below. (8’)

(1) Write out the product-of-sum expression of output F(W,X,Y,Z) for the circuit.

(2) Analysis all conditions that the static hazard may exit for the circuit, and indicate types of static hazard.

(3)Write out the minimal-product of output F(W,X,Y,Z) for the hazard-free.