Digital Electronics Term 2

Question 1

Iterative and incremental processes in software development

Answer 1

Iterative: fixing errors in the next iteration of the code, testing then repeat
Incremental: features are added one at a time

Question 2

Machine code, assembly language, high level definitions

Answer 2

MC: raw binary instructions, no abstraction
AL: symbolic notation for machine code instructions (ADD, SUB etc), slightly more human readable
HL: similar to natural language, lots of abstraction

Question 3

Compiler, assembler definition

Answer 3

C: converts high level code into machine code
A: converts assemply language code into machine code

Question 4

Portability in code definition and examples

Answer 4

Code being able to run on multiple different processors
Machine code = not portable. Would require rewriting for processors with different instruction sets
High level = very portable
Can use compilers for different processors means same code can be compiled multiple times

Question 5

Compliation process: 4 steps

Answer 5

1. Source code goes through Preprocessor. Involves being expanded with any files or macros
2. Compilation: source code converted into assembly code made of of mnemonics of the instruction set architecture
3. Assembly: assembly code is converted into binary machine code (object code) according to instruction format of the particular architecture
4. Linking: combining object code together with any library code to create an executable file

Question 6

Flags for c++ compliation stages (last one is special)

Other Flags for c++ compliation (two of them)

Answer 6

• E, -S, -c, g++
• Wall: outputs any warnings about the code
• O: optimises code, different levels (-O1, -O2, -O3)

Question 7

Why is the main() function special compared to others?

Answer 7

It defaults to returned 0 (hence why its int main() )

Other functions must explicitly contain a return statement

Question 8

What is the link between C and C++?

Answer 8

C++ is a superset of C

C code is also C++ code but not all C++ code is C code

Question 9

What can’t variable names contain in C++?

Answer 9

Spaces, commas or special charactors other than underscore

Question 10

Types of variable and their bit length: 6 in total. Think about sign and decimal places as well

Answer 10

Char (8 bits)
Short (16 bits)
Int (32 bits)
Long long (64 bits)
All can be unsigned or signed. Range example: char= 0-255 OR -128-127

Float (32 bits, 7 decimal places)
Double (64 bits, 16 decimal places)

Question 11

Pull up/pull down resistors on input pins

Answer 11

PU: pin reads logic 1 by default, logic 0 from input
PD: pin reads logic 0 by default, logic 1 from input

Question 12

Positive/negative logic on output pins

Answer 12

You can use a pin to sink/source small amounts of current
Positive:
Logic 1 on pin: 3.3 V
Causes current to flow from the pin
Pin acts as a current source
Negative: Logic 0 on pin: 0V
Causes current to flow from a supply into the pin
Pin acts as a current sink

Question 13

Mbed DigitalOut commands

Answer 13

write-set output to 1/0 (or use = as a shortcut)
wait-delay in code
BusOut-a way to address multiple pins at once (array with LSB first)
Example: array with 4 LED’s. Putting in 2 activates the second LED, 7 activates first 3 (think binary numbers)

Question 14

Mbed DigitalIn commands

Answer 14

read-returns 0/1 depending on whether its 0V/3.3V on the input pin
mode-changes pin to pull up, pull down or pull none

Question 15

PWN definition and uses

Answer 15

Pulse-width modulation
Outputs a periodic waveform controlled by changing its frequency and duty-cycle
Controls brightness of LEDs and speed of motors

Question 16

Duty-cycle definition and equation

Answer 16

Ratio of the 'on' time to the period
Remember f=1/T
DC= Tpw/T
DC=duty-cycle
Tpw='on' time

Question 17

Mbed PWM commands

Answer 17

PwnOut-sets a pin as a PWN output
Only works with certain pins
period-sets period of waveform
write/=-sets duty-cycle of waveform
Values must between 0.0 to 1.0

Question 18

ADCs definition

Answer 18

Used to convert an analogue voltage on a pin into a digital value
Useful as many sensors output an analogue voltage
REVISE how this is calculated

Question 19

Mbed ADC commands

Answer 19

AnalogIn-used to create a ADC input
Only works on certain pins
read-reads analogue voltage on pin
Returns number between 0.0 to 1.0

Question 20

Serial communication definition and types

Answer 20

Sending data between devices one bit at a time
In contrast to parallel communication where mulitple bits are sent together over a bus
Types: asynchronous and synchronous