12/11/2021, 10:14 Quiz: ELEC1601/ELEC9601 Final Exam
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ELEC1601/ELEC9601 Final Exam
 This is a preview of the published version of the quiz.
Started: Nov 12 at 10:10
Quiz Instructions
1 ptsQuestion 1
A computer encodes integers that lie in the range [ -81; 120 ] using two's
complement numbers.
How many bits are required to represent these numbers?


1 ptsQuestion 2
A computer system has 2^17 bytes of memory, where addresses are encoded
using 13 bits; how many bytes are there per memory cell?
1 ptsQuestion 3
Complete the truth table for the following boolean function:
12/11/2021, 10:14 Quiz: ELEC1601/ELEC9601 Final Exam
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A B C out
0 0 0
0 0 1
0 1 0
0 1 1
1 0 0
1 0 1
1 1 0
1 1 1
( +C) + C(A+B)
′
B
′
A
′
1 ptsQuestion 4
Study the following combinational digital circuit:
What is the value of Out1 when A = 0 and B = 1?
1 ptsQuestion 5
12/11/2021, 10:14 Quiz: ELEC1601/ELEC9601 Final Exam
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Study the following circuit and timing diagram:


What is the values for Out1 and Out2, during clock cycle 1 just after the falling
clock edge? Assume gates have negligible delay
Out1 = [ Select ]
Out2 = [ Select ]
1 ptsQuestion 6
Select all registers in the AVR architecture that are changed over the course of the
following instruction:
LD R28, -X
You can assume:
R28 initially has the value 4,
The address referenced by X contains the value 1
The address referenced by X+1 contains the value 0
The address referenced by X-1 contains the value 2
12/11/2021, 10:14 Quiz: ELEC1601/ELEC9601 Final Exam
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program counter
status register
'X' Register
R1 in register file
instruction register
'Y' Register
1 ptsQuestion 7
System B
Both finish at same time
System A
Not enough information to answer question
Suppose there are two computer systems:
System A has a 3 stage pipeline, and clock period of 50ns,
System B has a 5 stage pipeline, and clock period of 30ns.
Assume both systems receive their first instruction at the same time, which
system will be the first to complete the first instruction, assuming no pipeline
stalls?

1 ptsQuestion 8
A computer system has the value 0x333 in its stack pointer. The stack grows
(when you push data) towards lower memory positions. Suppose the system
executes the sequence of instructions:
PUSH R4
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PUSH R5
PUSH R6
POP R1
POP R2
What is the value of the stack pointer after this sequence?
(If it cannot be computed given the above information, enter the value 0)
1 ptsQuestion 9
Consider the 16 bit encoding used in the AVR architecture shown in the following
figure:
Assume the following values:
R3 = 3
R19 = 51
The instruction being executed (in machine code is): 0011 0011 0011 0011
After the instruction:
R3 has the value: (write this as a decimal value)
R19 has the value: (write this as a decimal value)
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( )
The Z flag in the status register has the value:
1 ptsQuestion 10
Status Register
Program Counter
Instruction Register
Stack Pointer
R1 in register file
'X' Register
Suppose the following command is executed:
jmp someSubroutine
Assume that the address of someSubroutine is held in the 'X' Register
Select all registers in the AVR architecture that are modified during this instruction:
1 ptsQuestion 11
Consider the following definitions in an assembly program:
d1: .byte 0, 1, 2, 3
If d1 is located in address 0xC33D, what is the value stored in that position after
executing the following instructions?
LDI R27, hi8(d1)
LDI R26, lo8(d1)
LDI R19, hi8(d1)
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LDI R18, lo8(d1)
ST -X, R18
1 ptsQuestion 12
An AVR assembly program defines the following variables and labels:
.section .data
D1: .byte 3, 6, 2
D2: .byte 10, 6, 4
What is the result if we subtract the address number of label D1 from the address
number of label D2
1 ptsQuestion 13
How many bytes are reserved in memory if an AVR assembly program has the
following data section:
.section .data
.byte 0x21, 0x2, 0x31
.space 90, 8
1 ptsQuestion 14
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What is the decimal value (base 10) held in R9 after the following sequence of
instructions?

LDI R18, 0x36
MOV R9, R18
SUB R9, R18
1 ptsQuestion 15
From the program memory
From one field of the instruction
From the data memory
From the register file.
Consider the AVR assembly instruction:
LDS R12, label,
(label has been defined in the data section).

Where is the microprocessor getting the operand loaded in R12?
1 ptsQuestion 16
Register X contains an address with value 0x012F.
12/11/2021, 10:14 Quiz: ELEC1601/ELEC9601 Final Exam
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The values in Data memory at addresses 0x012E, 0x12F and 0x0130 are 0x05,
0x05 and 0x08 respectively.
What is the value of Register 13 after the following instructions?
LD R12, X+
LD R13, X-
(write the base10 equivalent)
1 ptsQuestion 17
Suppose a program invokes a subroutine.
The subroutine requires 8 input parameters and 7 global variables to operate.
Assume the parameters are passed to the subroutine and result returned through
the stack. The result is 1 byte.
After the subroutine call, you wish to discard all input parameters and store the
result in R20.
How many times should you execute the command POP R20 after returning from
the subroutine?
1 ptsQuestion 18
Study the following program
It was generated by the compiler avr-gcc that uses the AVR libc library, so obeys
the convention for register management
LDI R5, 1
LDI R20, 2
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LDI R21, 3
PUSH R21
CALL my_subroutine ; Call the subroutine
POP R20
The result of the subroutine call was the integer 0x5123.
State the values (in base 10) in each of the following registers after the end of this
section of code. If unknown, type UNKNOWN.
R5:
R20:
R21:
R24:
R25:
1 ptsQuestion 19
Suppose a subroutine receives 5 1 byte parameters, returns a 1 byte result, and
the return address occupies 3 bytes. Internally, the subroutine needs 2 local
register. The subroutine returns a 1 byte result via the stack.
The program was generated by the compiler avr-gcc that uses the AVR libc library,
so obeys the convention for register management
Once in the subroutine, at the first instruction, what is the required displacement
(in bytes) from the top of the stack to the memory location where the result will be
stored?
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1 ptsQuestion 20
Study the following code (you can assume ". . ." refers to code that is not shown
main:
...
LDS R25, x
CALL subroutine2
...
PUSH R25,
CALL subroutine1
POP R0,
...
subroutine1:
...
MOV R25, R8
CALL subroutine2
...
MOV R24, R7 ; result
RET
subroutine2:
...
RET
How many calls to subroutine 2 are made in this code fragment (you can assume
that there all subroutine calls are shown in this code?
1 ptsQuestion 21
Study the following Boolean Expressions:
Show how this could be implemented on the following device:
F = ( )(A+B+C)
′
(A (B+ ))C
′
′
′
G = +CB
′
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1 ptsQuestion 22
Imagine a door lock that is password protected. It has two inputs, ‘x’, ‘y’, and a
reset button. The user can only press one input at a time.
To open the door, a user must first press the reset button. The user can then enter
one of two codes to unlock the door:
‘x’, ‘y’, ‘y’, ‘x’ or
y’, ‘x’, ‘y’, ‘x’
After the door has been unlocked, after 30 seconds it is automatically re-locked.

1. Draw the state transition diagram for the finite state machine (FSM) encoding
such a system. It must include the value of the inputs and output (door
unlocked or door locked). Try to use as few states as possible.
Take a picture of your final drawing and upload this to Canvas
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1 ptsQuestion 23
Consider the following fragment of code written in a high level programming
language:
int data[5] = {15, 25, 36, 12, 50};
int result = 0;
int count = 0;
while (count < 5)
{
result = my_function(result, data[count]);
count = count + 1;
}
Write a sequence of AVR assembly instructions equivalent to the previous code.
You can assume my_function is written elsewhere. You do not need to write this,
but you can access it by calling the subroutine.
.segment .data
data: .byte 15, 25, 36, 12, 50
result: .space 1, 0
count: .byte 0
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1 ptsQuestion 24
Complete the following program that monitors the status of a sensor connected to
digital PIN 5 (copy, then fill in gaps. Note that you do not need to fill in every gap).
The program should achieve the following:
When the sensor is not active, the program makes an LED connected to PIN 9
flash off and then on for half a second each and the message SENSOR
DOWN is sent to the serial communication link at 9600bps.
When the sensor is active, the LED should change its current value (if it is off,
it should change to on), then hold for 2 seconds and send the message
SENSOR UP through the serial communication link.

//Global variable declarations
bool sensor_on = false;
(gap 1) ..................................
(gap 2) ..................................
void setup()
{
(gap 3) ..................................
(gap 4) ..................................
(gap 5) ..................................
}
void loop ()
{
(gap 6) if (..................................)
{
(gap 7) ..................................
(gap 8) ..................................
(gap 9) ..................................
(gap 10) ..................................
}
else
{
(gap 11) ..................................
(gap 12) ..................................
(gap 13) ..................................
(gap 14) ..................................
(gap 15) ..................................
(gap 16) ..................................
(gap 17) ..................................
(gap 18) ..................................
}
}

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