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ee2000 9899a

# ee2000 9899a - CITY UNIVERSITY OF HONG KONG Course code&...

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Unformatted text preview: CITY UNIVERSITY OF HONG KONG Course code & title : EE20200 Logic Circuit Design Session : Semester A, 1998-99 Time Allowed : Two hours This paper has EIGHT pages. (Including this page and one page of Appendix) Course, code & title : EE20200 Logic Circuit Design Instructions to candidates: 1. This paper contains TWO parts. 2. Students MUST answer all the questions in Part A. And choose TWO questions from Part B. 3. Start a NEW page for EACH QUESTION. E— Materials, aids & instruments to be used during examination: Non-programmable portable battery operated calculator PART A (Answer all questions in this part - total of 40 marks) Question 1 Use Boolean algebraic techniques to simplify the following Boolean equation. (a®b+55+ab)(5+abc+5c+513) [6 marks] Question 2 Figure Q2 shows a circuit which implements the function f (A2, AHAO) = Y. Tabulate the truth table of the circuit and ﬁnd the minimum SOP expression of Y. [8 marks] 76508; _ E A0 HWH -Hx0 yopFJ Y A] — TJ—lxl yllp ] l l l % ”FF 1 ] E l 1 A2 '“E'WﬂE y3p ] E ; 5 “l l l ! E l t J l ‘ i Decoder J l 1‘ E L x0 yo :0» l i E i ] l i ix yl Ep—ﬁ F l l I 2P * ] y3p L -J Figure Q2 Question 3 Find the minimum SOP expression of the following Boolean function and use PLA to design the circuit. F(a, b, c, d)=HM(1, 4, 5, 6, 9,11)+ 2d(10,13, 14,15) [9 marks] Question 4 Use implication table method to obtain a reduced state table with minimum number of states from the following state table. NS/Output "U (/2 mommoouw [9 marks] Question 5 Figure Q5a shows a sequential circuit with an input x and output Q2. Assuming that the initial conditions for x, Q and Q2 are all Os, complete the timing diagram shown in Figure QSb for the given input x. (You do not need to consider the propagation delay time. You can use the timing diagram given in Appendix A to answer this question and attach it to your answer book.) [8 marks] Figure Q5b PART B (Choose two questions to answer - 30 marks for each question) Question 6 Figure 6 shows a block diagram for a motor control system. Switch S 1 controls the lubrication pump motor, M1. Switch S; controls the conveyor motor, M2. Switch 83 controls the band saw motor, M3. Switch 84 controls the cross—cut saw motor, M4. The motor that provides for lubrication of the conveyor (M1) must be on when the conveyor is on. The motor that drives the conveyor (M2) is on only when both switches SI and 82 are on. The band saw and the cross-cut saw motors require no lubrication, but they must never be on at the same time. If switches 83 and S4 are both turned on at the same time, the system must be completely shut down, including the conveyor and lubrication motors. Also, the cross—cut saw and the conveyor cannot be on at the same time. The control logic controls the motors to prevent any of the unallowed conditions from occurring. A logic 1 represents a ON condition of both S,~ and M. Motors S1 Motor Conveyor From S2 drive switches interface Band saw Cross-cut aw Figure Q6. (a) Tabulate the tmth table of the control unit. [6 marks] (b) Find the Boolean expression of M1, M2, M3 and M4 . Your result should be in minimum SOP form. [8 marks] (c) Design the control logic of M1 using NAND gates only. Draw the circuit. [5 marks] (d) Use a 4-to-1 lines mutliplexer and suitable logic gates to implement the control logic of M1. Draw the circuit. [6 marks] (e) The input of an inverter (74805) with open-collector output is used to connect to M . A LED circuit is required to connect to the output of 74805 to indicate a ON condition of M. For a supply voltage of 5V, ﬁnd the minimum value of a pull—up resistor and draw the LED circuit. The electrical speciﬁcations of 74805 and LED are given in Table Q6. [5 marks] Question 7 Figure Q7 shows a bidirectional universal shift register and its functional table is given in Table Q7. Figure Q7 Table Q7 a. The above register can be used to perform serial data to parallel data conversion. Complete the timing diagram given in Appendix A according to the following steps for each serial-to-parallel conversion. (You must consider the propagation delay time when completing the timing diagram.) i. Clear the output; ii. Start to shift the 4 bits serial data to the register; iii. Hold the data for one clock cycle; iv. Repeat step i. [10 marks] b. Draw the circuit diagrams of a basic ring counter and a Johnson counter using the above register and suitable logic gates. Brieﬂy describe the initialization steps for both counters. (You must show all the pin connections including external inputs.) [10 marks] c. i. Draw a circuit diagram of a 4-bit serial adder based on the above registers, a full- adder module and other logic components. Brieﬂy describe the functions of the components used in your design. [7 marks] ii. Brieﬂy describe the setting of control signals and their associated functions. [3 marks] Question 8 A serial data line is connected to an input of a synchronous sequential circuit. This circuit is used to count the number of Is of the latest three consecutive bits received from the serial input x. This circuit has two output bits yLyo to represent the number of 1s. Table Q8 shows the state assignment of this counting circuit. The three-bit state assignment represents the three consecutive bits received and the leftmost digit represents the latest binary data received from the serial input x. State State Assignment Assignment S4 100 SS 101 S6 110 S7 111 Table Q8 a. Use Moore machine to design a state diagram that describe the operation of the counting circuit. [7 marks] b. Tabulate a state table from (a). [3 marks] c. Use JK ﬂip—ﬂop(s) and other necessary logic gates to design the counting circuit. Draw the circuit. [16 marks] d. Devise a simple circuit from the output circuit of part (c) to produce an even parity bit according to the received three consecutive bits. [4 marks] ***** END ***** Agpendix A Student N 0: Programme: Timing diagram for Question 5: Mode SO Control Inputs S1 clear Serial Ri Data Inputs 03 ' Outputs 02 Q1 L.' ...
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ee2000 9899a - CITY UNIVERSITY OF HONG KONG Course code&...

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