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Cork Institute of Technology
Bachelor of Engineering (Honours) in Electronic Engineering – Stage 2
(NFQ – Level 8)
Summer 2007
Digital Systems and Microprocessors
(Time: 3 Hours)
Answer any68000 Instruction Sets are available. FIVE questions Blank Before & After Tables available
Examiners: Prof. G. HurleyDr. S. Foley Dr. W.P O’Connor
Q1 Assume the values shown in Table.1-1 exist for the first instruction [(a)] only , then show what happens when each of the instructions in Table.1-2 is executed. Brief comments and the status of the flags are required. (Use the Before & After table provided). Table.1- Values that exist at the start of each instruction.
D0 = $12345678 D1 = $456789AB D2 = $AB12DE34 D3 = $ D4 = $00002000 D5 = $FFFFFFFF D6 = $2346C001 D7 = $FE89AB
A0 = $00400500 A1 = $00400544 A2 = A3 = A4 = A5 = A6 = A7 =
-- Memory Contents CCR = 00000000 (^2)
400500 1234 5678 ABCD EF98 9876 5421 FEDC BA 400540 CAFE BAD8 BC12 DEF0 D3C4 F1E2 6251 7328 Instructions to be executed. a) SUB.W D7, D24 b) MOVE.L 8(A0), 2(A1) c) MOVE.W D6, (A0) + d) ADD.W 6(A1), D e) ROL.W #3, D2 f) LSR.L #2, D g) ASR.W #3, D5 h) CMP.W #$BC72, D i) ADD.W 4(A1), D4 j) MOVEA.W D1, A Table.1-2 (20 marks)
Q2 (a) Identify and briefly explain each item of information in the two lines of code below. Then describe the sequence of steps involved when the MC68000 MPU executes the two instructions (Table 2(a)). 00400400 : 2E3C0000012C MOVE.L #300,D 00400406 : 11460010 MOVE.B D6,$10(A0) Table.2(a) (4 marks) (b) State the addressing mode of each operand in the instructions below. (i) MOVE.W #$400600, – (A0) (ii) MOVE.W 4(A0), $400400 (2 marks) (c) Identify and rectify the deliberate errors in each of the following instructions: (i) MOVE.B – (D5), A (ii) MOVE.W #$12345678, $ (iii) MOVE.B +(A1), # (iv) ROR.W #F, D0 (4 marks) (d) Write a M68000 based assembly language program to generate the first 8 numbers of the Fibonacci series (0, 1, 1, 2, 3, 5, 8, 13, …..). A detailed flowchart and comments should accompany your code. (10 marks)
Q3 (a) Draw a detailed block diagram of the MC68000 microprocessor, showing all registers and busses. (4 marks) (b) If a RAM chip is described as an 1MByte device, state the pins you would expect to find on its pinout diagram, showing all workings. (4 marks) (c) A 68K-microcomputer system requires 2Mbytes of RAM, with a base address $600000. RAM chips of capacity 512KB are available, each with a single active-low CS input. (i) Devise a complete memory map, which shows the addresses occupied by each 512KB chip. (ii) Draw a detailed block diagram of the microcomputer, highlighting 512Kbytes of RAM, address decoding, microprocessor control lines and address and data lines. (12 marks)
Q5 (a) In relation to the input/output unit of a computer, explain the difference between serial and parallel ports – use diagrams to illustrate your answer. (6 marks) (b) The message DLX2 is sent using asynchronous ASCII with even-parity, 1 start-bit and 2 stop-bits. A data storage oscilloscope is used to read the transmit line. What is the bit pattern that appears on the oscilloscope’s CRT. ASCII values are : D = 44 16 , L = 4C 16 , X = 58 16 , 2 = 32 16 (6 marks) (c) Describe fully the MC68681/ DUART (include registers/control lines/handshaking etc.). Explain the function of each part of this device. Hence show its connections to the MC68000 MPU. (8 marks)
Q6 (a) Use the truth-table in Table.6-1 to implement the 7,4 Hamming Code (i.e. 4 information bits, M 4 , M 3 , M 2 , M 1 and 3 Parity bits, P 3 , P 2 , P 1 ) using a decoder and additional gates. Information Bits Parity Bits M 4 M 3 M 2 M 1 P 3 P 2 P (^1) 0 0 0 0 0 0 0 0 0 0 1 0 1 1 0 0 1 0 1 0 1 0 0 1 1 1 1 0 0 1 0 0 1 1 0 0 1 0 1 1 0 1 0 1 1 0 0 1 1 0 1 1 1 0 0 0 1 0 0 0 1 1 1 1 0 0 1 1 0 0 1 0 1 0 0 1 0 1 0 1 1 0 0 1 1 1 0 0 0 0 1 1 1 0 1 0 1 0 1 1 1 0 1 0 0 1 1 1 1 1 1 1 Table.6-1 : The 7,4 Hamming Code (5 marks)
(b) Explain carefully why a stack is needed in a computer and show, using diagrams, how it is organised and controlled in a MC68000-based computer. (5 marks) (c) Describe in detail the sequence of events that take place when the JSR instruction below is encountered (assume A7 = $400600 initially). 400400 4EB900400500 JSR $ 400406 …………….. (4 marks) (d) Demonstrate your understanding of exception processing with regard to MC68000 MPU. Thus, indicate how interrupts are handled within the microprocessor. (6 marks)
