National University of Computer and Emerging Sciences
School of Engineering
Islamabad Campus
Serial No:
EE303-Microprocessor
Interfacing & Programming
Final Exam
Total Time: 03 Hours
Total Marks: 120
Wednesday 18 December, 2019
Course Instructors
________________
Dr. Waseem Ikram
Engr. Azhar Rauf
Signature of Invigilator
____________________________ _______ __________ _____________________
Student Name
Roll No
Section
Signature
DO NOT OPEN THE QUESTION BOOK OR START UNTIL INSTRUCTED .
Instructions:
1. Verify at the start of the exam that you have a total of six (6) questions printed on
fourteen (14) pages including this title page.
2. Attempt all questions on the question-book and in the given order.
3. The exam is open books, closed notes. Please see that the area in your threshold is
free of any material classified as ‘useful in the paper’ or else there may a charge of
cheating.
4. Read the questions carefully for clarity of context and understanding of meaning
and make assumptions wherever required, for neither the invigilator will address
your queries, nor the teacher/examiner will come to the examination hall for any
assistance.
5. Fit in all your answers in the provided space. You may use extra space on the last
page if required. If you do so, clearly mark question/part number on that page to
avoid confusion.
6. Use only your own stationery and calculator. If you do not have your own
calculator, use manual calculations.
7. Use only permanent ink-pens. Only the questions attempted with permanent inkpens will be considered. Any part of paper done in lead pencil cannot be claimed
for rechecking.
Total Marks
Q-1
Q-2
Q-3
Q-4
Q-5
Q-6
Total
20
20
20
20
20
20
120
Marks Obtained
Assessment of CLO CLO 2 CLO 4 CLO 4 CLO 4 CLO 5 CLO 5
Vetted By: ____________________________Vetter Signature: ____________________
National University of Computer and Emerging Sciences
School of Engineering
Islamabad Campus
CLO-02: Describe the AVR based microcontroller architecture, its internal registers and
instruction set.
Q1. Briefly answer the following short Q/A on instructions and addressing modes.
[20]
a. Name four types of memory found in AVR ATMega32 systems and their typical sizes.
[1]
GPR (32), IO (64), SRAM (2048), External SRAM, EEPROM
b. What would be the exact instructions to use if we want to substitute:
a. LDS R17, $29 with the corresponding IN instruction?
[2]
IN R17, UBRRL or IN R17, $09
b. STS R29, $67 with the OUT instruction?
Not possible, there is no corresponding IO Register for address $67
c. Write STS 55, 0x15 in pneumonic assembly form (i.e. refer to the registers by name).
[1]
STS DDRB, R21
d. Where does RISC stand with respect to different addressing modes? Elaborate. What
benefit of indirect and indexed addressing modes?
is
the
[2]
RISC wants reuse and simple instructions. So, RISC microprocessors opt for few, most essential
addressing modes. They avoid duplication and lot of complex indexing and indirect addressing.
Benefit is the ability to use dynamic counting and looping as well as pointers in code where
the count value is changed on the fly.
e. Will assembly language programs written for ATMega32 work on ATMega128 version? Why or
why not?
[1]
Since the register address boundaries will be different for both, it may work if only
pneumonics are used to address registers. However, if physical or IO hex addresses are used,
the program will most likely not run.
f.
Even though there are three register sets used for indirection, they differ in the way they can be
used. Mention the major differences between these three registers.
[1]
All three are 16-bit registers. Register X cannot be used in the displacement mode while Y and
Z can be. Register Z is the only one that can be used to load from program memory – others
cannot.
Final Exam
Fall 2019
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National University of Computer and Emerging Sciences
School of Engineering
Islamabad Campus
g. What is the difference between Little Endian and Big Endian architecture? Which one is ATMega
32?
[1]
h. How is the overflow flag affected by the Indirect addressing mode post-increment and predecrement operations?
[1]
i.
What are the benefits of using IN/OUT vs. LDS/STS instructions?
j.
Given the below memory contents and code, indicate the final contents of the registers used and
memory. Indicate one register for the pointer registers (e.g. use Z for ZL and ZH).
[4]
LDI
DEC
LDS
LD
MOV
LDI
LDI
ST
INC
ST
26, 0x01
26
$1B, 26
R21, X
R23, R21
28, 0x01
$1D, 0x03
Y, R23
R23
-Y, R23
[1]
Address Bus (hex)
0100
0101
0102
0103
0104
Data Bus (dec)
67
99
-56
0
82
Register
Contents
k. Suppose seismic data from two sensors in local magnitude (ML) scale, commonly referred to as
"Richter scale", are stored in two areas of contiguous AVR SRAM memory. Write a program to
compare the two sets of data and display the higher value on Port C continuously. First set is at
location 0x500 and the other at 0x600. Each set has 10 data values
[5]
Final Exam
Fall 2019
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National University of Computer and Emerging Sciences
School of Engineering
Islamabad Campus
CLO-04: Design hardware interface using datasheets and write software routines to fully
exploit the capabilities of the devices.
Q2. Two AVRs A and B are connected to each other through serial link as shown in figure
below. The AVR ‘A’ reads character data from its RAM and transmits it serially to AVR ‘B’.
The assembly code shows the functionality of AVR B controller. Answer the questions for
the code and explanation given above.
[20]
Here:
AVR
AVR
AVR A
AVR B
LDI R20, 0
; counter which keeps track of the specific character
LDI R16, 0xFF
OUT DDRB, R16
LDI R16, 0x90
OUT UCSRB, R16
LDI R16, 0x86
Rx_ISR: IN R16, UDR
OUT UCSRC, R16
CPI R16, ‘f’
LDI R16, 0x33
BREQ Equal
OUT UBRRL, R16
RJMP Exit
SEI
Equal: INC R20
OUT PORTB, R20
Exit:
RETI
RJMP Here
a. What are necessary condition(s) to enable communication between the two AVRs?
[3]
b. What function is performed by AVR ‘B’ controller as per the assembly code given?
[2]
Final Exam
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School of Engineering
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c. Assume the interrupt for AVR ‘B’ develops a fault so interrupts no longer occur. Convert
the interrupt based AVR ‘B’ assembly code shown above into a polling based code. [10]
Final Exam
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d. Connect the two processors for full-duplex communication. Is it possible to generate the
serial communication clock baud rate using an external clock instead of the internal
processor clock?
Final Exam
[5]
Fall 2019
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National University of Computer and Emerging Sciences
School of Engineering
Islamabad Campus
CLO-04: Design hardware interface using datasheets and write software routines to fully
exploit the capabilities of the devices.
Q3. A temperature monitoring system is to be implemented. The block diagram of the system is
shown below. The temperature sensor is interfaced with analog input channel ADC0 of AVR.
The temperature is measured after every 1 minute interval. Eight LEDs are connected to Port D
of AVR to show the measured temperature. The buzzer is connected with PB1. It is turned on if
the temperature is above the threshold otherwise it remains off.
A 555 chip is configured to generate 1 Hz pulses and connected to T0 pin of AVR controller and
AVR uses Timer 0 to measure 1 minute interval.
[20]
Temp.
Sensor
Buzzer
AVR
LEDS
a. Write the main program which should perform following tasks:
• Declare pin T0 and ADC0 as input and PORT D and PB1 as output.
[2]
• Configure Timer 0 to measure the interval of 1 minute and enable its interrupt.
[4]
• Display read temperature on Port D continuously. Assume that the sensed temperature can
be accommodated in single byte.
[2]
Final Exam
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National University of Computer and Emerging Sciences
School of Engineering
Islamabad Campus
b. Write the ISR which will be called every time the counter counts an interval of 1 minute. The ISR
should perform following tasks:
•
•
•
Write the code to turn on the ADC module of the AVR, select the conversion speed of AVR
(clk/4) and select ADC channel and reference voltage (Vref= 2.56 V internal). The ADC data
should be right justified.
[6]
Write the code to sample and digitize the temperature and reads its value.
[4]
Compare the read value of temperature with threshold value of 350. If it is above the
threshold, the buzzer must be turned on otherwise it must remain off.
[2]
Final Exam
Fall 2019
Page 8 of 14
National University of Computer and Emerging Sciences
School of Engineering
Islamabad Campus
CLO-04: Design hardware interface using datasheets and write software routines to fully
exploit the capabilities of the devices.
Q4. An AVR is setup to test its serial interface (transmitter and receiver) and also the wire link which
connects the transmitter to the receiver. This done by connecting the TXD pin of the AVR to the
RXD pin. The transmitter then transmits a test message to the receiver. The transmitted test
message is compared with the received test message. The serial communication interface is
verified if the two messages match. The testing can be repeated at different baud rates. [20]
a. Write assembly code which initializes the USART for asynchronous communication, no parity, 1
stop bit and 8-bit character.
[4]
LDI R16, 0x86
OUT UCSRC, R16
; asyn, parity disabled, 1 stop, 8-bit char
LDI R16, 0x33
OUT UBRRL, R16
; 9600 baud
LDI R16, 0x18
OUT UCSRB, R16
; enable TX and RX
b. Write assembly code which transmits a message ‘TEST MESSAGE’ and receives the same and
stores the received message in memory.
[10]
LDI XH, 0x05
LDI XL, 0x00
LDI YH, 0x06
LDI YL, 0x00
AGAIN:
[1]
LPM R17, X+
CPI R17, 0
BREQ EXIT
RCALL TMT
RCALL RCV
RJMP AGAIN
[2]
MSG
.DB ‘TEST MESSAGE’,0
[1]
TMT:
SBIS USCRA, UDRE
EXIT:
.ORG $500
RJMP TMT
OUT UDR, R17
RET
RCV:
[2]
SBIS UCSRA, RXC
RJMP RCV
IN R17, UDR
ST Y+, R17
RET
Final Exam
[4]
Fall 2019
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National University of Computer and Emerging Sciences
School of Engineering
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c. Write assembly code which compares the ‘TEST MESSAGE’ with the received message. If
the sent and received messages match Port A displays 00 otherwise it displays FF
[6]
COMPARE:
LDI XH, 0x05
LDI XL, 0x00
LDI YH, 0x06
LDI YL, 0x00
NEXT:
[1]
LM R16, X+
LM R17, Y+
CPI R17, 0
BREQ MATCH
CP R16, R17
BRNE NOMATCH
RJMP NEXT
NOMATCH:
[3]
LDI R17, 0xFF
OUT PORTA, R17
RJMP EXIT
MATCH:
LDI R17, 0
OUT PORTA, R17
[2]
EXIT:
Final Exam
Fall 2019
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National University of Computer and Emerging Sciences
School of Engineering
Islamabad Campus
CLO-05: Design and implement stand-alone microcontroller based systems.
Q5. A stepper motor based robot can move precise steps in the forward and backward direction.
The user specifies the direction and steps and the robot moves precisely in the specified
direction.
[20]
a. Draw the connection of the stepper motor to the AVR through a driver. The stepper motor is a
unipolar motor. The stepper motor rotates 1o with each step. Robot wheel diameter is 10 cm. How
much distance will the robot cover if 0b0010101 specifies the number of steps.
[8]
[6]
Distance covered = (21/360) x 10 = 1.83 cm [2]
b. Write assembly code which reads an 8-bit value from Port A. The distance to be moved is
calculated and the robot moves in the forward and backward direction for the specified distance.
The MSB specifies the forward (MSB = 1) or backward (MSB = 0) direction of movement. The
remaining 7 bits specify the steps.
[12]
LDI R20, 0xFF
OUT DDRB, R20
LDI R20, 0
OUT DDRA, R20
LDI R20, 0x66
L1:
OUT PORTB, R20
IN R16, PINA
SBRS R16, 7
BRGE forward
ANDI R16, 0x7F
BKAgain: LSR R20
BRCC OV1
ORI R20,0x80
OV1:
OUT PORTB, R20
RCALL DELAY
DEC R16
BNEQ BKAgain
RJMP L1
Final Exam
; Port B o/p
; Port A i/p
[2]
;
;
;
;
;
;
[1]
step pattern
read input
check for direction
forward
get number of steps
next step
[3]
; step pattern
; last step backward?
[3]
Fall 2019
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forward: ANDI R16, 0x7F
FDAgain: LSL R20
BRCC OV2
ORI R20,0x01
OV2:
OUT PORTB, R20
RCALL DELAY
DEC R16
BNEQ FDAgain
RJMP Ll
Final Exam
Islamabad Campus
; get number of steps
; next step
; step pattern
; last step forward?
[3]
Fall 2019
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National University of Computer and Emerging Sciences
School of Engineering
Islamabad Campus
CLO-05: Design and implement stand-alone microcontroller based systems.
Q6. The speed of a variable speed DC motor is proportional to the pulse width of an input
signal. Thus wider the input pulse higher is the motor speed and vice versa. The
following specification are used to implement the DC motor speed controller:
[20]




XTAL = 8 MHz
Pulse width of the input signal is in the range of 1 μs to
255 μs
The frequency of the Phase correct PWM mode used to
control the DC motor speed is 1.961 kHz.
Since the motor speed is proportional to pulse width
therefore:
Input signal pulse width
255 s
191 s
128 s
64 s
Duty cycle for DC motor
100%
75%
50%
25%
a. To which pin of the AVR is the input signal
connected?
[2]
b. Draw the connection of the DC motor with the AVR through a driver circuit. Timer 2 is
used to generate the Phase correct PWM to control the DC Motor speed.
[6]
c. Write assembly code for the speed of the DC motor based on the input pulse width. [12]
A.
a. ICP1 (PD6)
b.
Connected to OC2 (PD7) pin
Final Exam
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c. Fgenerated wave = Foscillator/510N
Islamabad Campus
N = Foscillator/510 Fgenerated wave = 8000/510 x 1.961 = 8
BEGIN:
[1]
LDI R20, 0x00
OUT TCCR1A, R20
L3:
L1:
LDI R20,0x42
; input capture on rising edge
OUT TCCR1B, R20
; prescalar divide/8
SBI DDRD, 7
; set OC2 output
[2]
IN R21, TIFR
SBRS R21, ICF1
; check flag for edge
RJMP L1
; no edge goto check again
IN R16, ICR1L
; save rising edge arrival time
OUT TIFR, R21
; reset flag
LDI R20, 0x02
; reconfigure for falling edge
[3]
OUT TCCR1B, R20
L2:
IN R21, TIFR
SBRS R21, ICF1
; check flag for edge
RJMP L2
; no edge goto check again
IN R22, ICR1L
; save falling edge arrival time
OUT TIFR, R21
; reset flag
SUB R22, R16
; calculate pulse width
OUT OCR2, R22
; duty cycle
[3]
LDI R20, 0x62
Final Exam
OUT TCCR2, R20
; non-inverted mode, prescalar div/8
RJMP L3
; measure next pulse
Fall 2019
[3]
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