Computer Hardware Flashcards
1
Q
How do computers represent data?
A
With bits (an instance of a state)
2
Q
What is a bit
A
A bit represents a state (1 or 0)
3
Q
What is a nybble (nibble, or nyble)
A
Four consecutive bits
4
Q
What is a byte?
A
Eight consecutive bits
5
Q
When talking about memory what is the concept of a “word”
A
Basic unit of data that a cpu can process at one time.
6
Q
How many possible characters in ASCII and why?
A
2^7, so 128.
This is because 2 (states 1 or 0) and ASCII characters are stored in 7 bits.
7
Q
What is a combinatorial logic circuit?
A
Circuit whose digital output are dependent only on their digital inputs (works in binary, no memory).
8
Q
All logic gates have two inputs and one output , except for ______.
How does this logic gate behave?
A
NOT (1 input, 1 output)
Invert (E.g., if input is 1, it will invert it and output 0)
9
Q
How many functions for 1 input and 1 output?
A
4
False, Indentity, True, and NOT
10
Q
How many functions for 2 input and 1 output?
A
16
Because there are 4 input combinations: (00, 01, 10, 11) . For each combination there are two possible outputs, therefore 2^4 = 16.
11
Q
What does the AND logic gate look like?
And how does this logic gate work?
A
2 inputs going into a ‘D’ shape, with one output coming off the other end of the D.
Gives true (1) if both are same.
12
Q
What does the NAND logic gate look like?
And how does this logic gate work?
A
Same as AND but with a small circle at the end of the D.
True (1) when they are both NOT true.
13
Q
What does the OR logic gate look like?
And how does this logic gate work?
A
2 inputs going into a ‘shield’ shape, with one output coming off the other end of the D.
True (1) when either input or both are true.
14
Q
What does the EOR/XOR logic gate look like?
And how does this logic gate work?
A
Similar to or, but an arch is on the top of the shield.
You can have one or the other, but can’t have both.
15
Q
What a boolean expression for both the ‘OR’ and ‘AND’ logic gates.
A
Or: Y = A + B
And: Y = A * B
16
Q
Write a diagram to represent 2 input, 2 output for a circuit containing a ‘XOR’ and a ‘AND’ logic gate.
A
Combine both with both input bits going to both logic gates.
17
Q
What is a Ripple Carry Adder?
A
Each full adder takes the current bits being added, along with any carry from the previous addition stage, and produces the sum and carry output, which is then used in the next stage.
18
Q
What is a 3-bit Parity Generator
A
A 3-bit parity generator is designed to ensure that the total number of 1s in the 3-bit binary sequence is always odd, which is typically achieved by setting the parity bit to 1 or 0 to make the total count of 1s odd. This is often used for error checking and correction purposes.
19
Q
Write an equation so P is always true (3-bit Parity Generator)
A
P = (notA * notB * notC) + (A * B * notC) + (A * notB * C) + (notA * B * C)
20
Q
How do 7-segment Digital Displays work?
A
They form an 7 with lines, and bits symbolise which lines to light up.
21
Q
What is the Boolean Operator Precedence.
(order in which Boolean operators (such as NOT, AND, and OR) are evaluated)
A
1st - NOT
2nd - AND
3rd - OR
22
Q
What is a transistor?
And how do they work?
A
An electronic switch.
B = Base, C = Collector, E = Emitter
0v to B = Switch opens, C is disconnected from E
Apply v to B = Switch closes, C is connected to E.
23
Q
What is a demultiplexer?
A
A multi-way switch where the address selects which output receives the input.
E.g., 00 = Y0, 01 = Y1, 10 = Y2, 11 = Y3
24
Q
What is a Set-Reset Latch?
Draw a table to represent S R inputs and their corresponding actions.
A
Used to set and unset latch.
S | R | Action
0 | 0 | None
0 | 1 | Q = 0
1 | 0 | Q = 1
1 | 1 | Invalid
25
Can you make the Flip-Flop using only NAND gates?
Yes, by inverting S and R.
26
What is a D-type Flip-Flop
Data Input (D): The value at the D input represents the data that you want to store in the flip-flop.
Clock Input (CLK): The clock input determines when the data at the D input is sampled and transferred to the Q output. The data is transferred on either the rising or falling edge of the clock signal, depending on the specific type of D flip-flop (positive-edge-triggered or negative-edge-triggered).
Q Output: This is the output of the flip-flop, and it reflects the value of the D input when the clock edge occurs.
Q' Output: This is the complement of the Q output (inverted Q). If Q is high, Q' is low, and vice versa.
USED FOR:
Data Storage
Synchronization
Sequential Logic
Edge Detection
Frequency Division
Memory Elements
Data Transfer
Control Logic
Serial-to-Parallel Conversion
27
What is a T-type Flip-Flop
A T-type flip-flop, also known as a toggle flip-flop, is a type of digital circuit used in electronics and digital logic design. It has a single input (T) and a single output (Q). The purpose of a T-type flip-flop is to change its output state based on the input signal.
Here's how a T-type flip-flop operates:
When the input (T) is set to 0, the flip-flop retains its current state. In other words, the output doesn't change.
When the input (T) is set to 1, the flip-flop toggles its state. If the output was 0, it changes to 1, and if it was 1, it changes to 0. This is why it's called a "toggle" flip-flop.
T-type flip-flops are used in various applications, including counters and frequency dividers, where the toggling behavior is valuable for creating clock signals and binary counting sequences.
28
What is a JK-type Flip-Flop
A JK-type Flip-Flop is a digital circuit element with two inputs, J (set) and K (reset), and a clock input.
If we feed 0 0 to the inputs (Let's say J and K) it does not change the clock.
If we feed 0 1, it resets it.
If we feed 1 0, it sets it.
If we feed 1 1, it toggles it (Gives not what Q was before)
29
How can we change the JK-type Flip-Flop into a T and D flip-flop.
T: Set K = J
D: Set K = notJ
30
How does an Asynchronous Ripple Counter work?
What if we use a 2-bit Ripple Counter?
Switches between 0 and 1 each clock cycle. (Output is half the frequency of the input square wave, or clock cycle)
First will be 0, 1, 0 ,1, 0, 1 ...
2-bit will be 00, 11, 00, 11...
And so on.
31
Show an example of Synchronous Counter bits
1, 0, 1, 0, 1, 0
00, 01, 10, 11, 00
32
What do Sequential Circuits do?
Store state between each use (i.e., they have memory).
33
How can you detect inputs with state transition diagrams?
Given the need to find 11011. Write a state transition diagram for this.
34
What is a Tristate Buffer, and what are it's three states?
What are the combinations are their corresponding outputs.
High (1), Low(0), High-Impedance(Z).
- Output is either the input (D) or high-impedance.
D | E | Y
0 | 0 | Z
0 | 1 | 0
1 | 0 | Z
1 | 1 | 1
When E is 0 (disabled), the output Y is in a high-impedance state (Z), regardless of the value of D.
When E is 1 (enabled), the output Y is equal to the value of D.
35
How are buses represented?
With widow arrows (which represents several wires).
36
What are some 'buses' features?
- Used to communicate with parts of the computer.
- Only one transmitter at a time.
- Only one addressed bus can respond (tristate buffer disconnects other devices).
- 2 levels of buses; internal to chip & external to chip.
37
Memory size is dependent on ____?
address bus 'width'
2^n bytes for n-lines on the address bus: 2^8 = 256B
So 2^16 = 64KB
2^32 = 4GB
...
38
How are flip flops grouped?
Into bytes (or larger).
Flip-flops can be grouped into various configurations based on the specific design requirements, which may or may not align with byte-sized or larger data units.
39
Memory made from flip flops are called ____?
Static Ram:
- Used in the CPU cached RAM.
- Used anywhere a small amount of fast RAM is needed.
- SRAM is expensive.
Note: The main memory of your computer is Dynamic Ram.
40
How is Dynamic Ram stored?
Explain the aspects of capacitors, that demand attention for Dynamic Ram.
On a capacitor as a charge
0 = No Charge
1 = Charged
Capacitors are leaky
- Need to be periodically refreshed.
- A read operation drains the capacitor.
41
What's another name for Read-Only-Memory
Non-Volatile Memory
42
What is an ALU (Arithmatic Logic Unit)?
What components does it have?
Performs arithmetic operations and performs logical operations
- Addition, subtraction, etc
- AND, OR, SHIFT, etc
- Two inputs.
- AND logic gate
- Add circuit
- Load
43
What does the control unit do?
Generates control signals:
- Connect to registers on the bus.
- Control the function of ALU.
- Provides timing signals to the system.
44
What are registers?
What does it do when connected to the ALU and control unit?
Memory cells with names: A bunch of flip-flops storing values.
Typically holds data same size as the memory words.
Stores values, and feeds it back in.
45
What are the special purpose registers and what do they do?
The program counter
- Stores the address of the current instruction.
The accumulator
- Source of one of the operands.
- Destination of the result.
The status flags
- Individual bits store information about results of the operations.
- Result of the last instruction was negative, zero,
or positive.
- Carry from the most recent arithmetic operation.
- Overflow occurred during the last instruction.
46
What are CPU instructions?
(6809 Instruction Structure)
Bit patterns
Can be split into a number of fields
- Operation to be executed
- Address in memory
- Which registers (or memory cells) to use as operands
- Where to place the result (registers or memory)
Long Explanation:
'cmpb #9' Let's break it down:
Operation to Be Executed: 'cmpb' represents the operation to be executed. 'cmpb' stands for "compare byte." It's an operation that compares the value of a byte-sized operand.
Address in Memory: The '#' symbol is often used in assembly language to represent an immediate value, which means that the value 9 is the constant operand to be used in the comparison. In this context, there might not be a specific memory address involved, as the value 9 is directly provided in the instruction.
Operand: The operand is the value 9 that you want to compare.
Where to Place Result: The 'cmpb' instruction does not produce a result that is typically stored anywhere. It is used for comparing values. The result of the comparison is stored in status flags, such as zero flag, carry flag, or sign flag, depending on the architecture. These flags are used to make decisions in conditional branches (like jump if equal, jump if not equal, etc.) that follow the comparison.
47
What are the Three Key Concepts of Von Neumann Architecture?
- Data and instructions are stored in a single read-write memory.
- Contents of memory are addressable by location, without regard to the type of data contained.
- Execution occurs in a sequential fashion, unless explicitly altered, from one instruction to the next.
48
What is machine code, coded in?
1's and 0's
49
How much memory does 6809 have?
64KB 2^16
- Though, we only do math with 8 bit numbers, it is a 16 bit address bus.
- 64,000KB of memory broken into memory (256 pages, 2^8).
50
What bits are the 6809 registers.
A, B = 8 bit (does math with them)
All the rest are 16bits (access memory).
51
What are the 6809 registers are what are they used for?
Index Register (X) & (Y)
Makes accessing indexes in memory easier.
User Stack Pointer (U):
For own purposes.
System Stack Pointer (S):
Used for function calls, keeps track of processes.
Program Counter (PC):
Which instruction we are executing.
D (A and B):
52
What are the 6809 Condition Codes (CC), and what do they do?
The Condition Codes (CC) holds information about the result of the previous operation.
N - If last math operation resulted in negative.
Z - If last math operation resulted in 0.
V - Overflow, meaning result of operation cannot be represented within the valid range for signed numbers.
C - Carry or borrow of most significant bit.
53
What do instructions consist of?
Are instructions different length?
(6809 assembly)
(1) One or more fields:
- The mnemonic opcode (e.g., return to subroutine).
- And (optionally) parameters called operands (e.g., GOTO (bra more)).
(2) Yes, they often are.
54
Discuss Operand Symbols
immediate (if no # is given then it's an address, otherwise it is NOT an address)
$ hex value
% binary value
55
List a few aspects of Assembly Languages.
- Can't declare variables (only use registers).
- Only loop constraint is GOTO
- Can only compare using integers and bytes.
- Can only branch if comparison matches certain conditions.
56
What location does SCREEN start with 6809
$0400
57
How do you format creating a constant in 6809?
58
What is an important note to remember when using registers in 6809.
We need to restore them:
Save at start:
- pshs
Restore when done:
- puls
59
How can you store a string into memory? (Assembly)
message:
.byte "", 0
What does the 0 do? Our subroutine only stops when it sees the $00
60
What does LEA (Load Effective Address) do?
Does computation to find where to get it from.
61
What are CMOC 6809 calling conventions? / rules
- A routine must preserve Y, U, S and DP.
- Parameters are pushed on the stack in reverse order.
- Caller must pop them off the stack after the call.
- Chars -> int
- Unsigned char -> unsigned int
- Return 8 bit value in B.
- Return 16 bit values in D.
62
What are some key notes with C routines?
A routine can be scoped to it's current file
- static
Routines must be declared before use (.h file)
- extern int eleven(void)
63
What word is used to represent constants
const
64
Enums, what are they?
Hold constant values, which can only be integer
65
What is different about C variables to Java?
C does not initialise variables
66
What does typedef do in C?
Struct example{}
- struct example G
typedef Struct example{}
- example G
67
What does static mean in C
- Scope of routine local to this source code file.
- This variable maintains its value between calls.
68
What does volatile do in C?
Do NOT optimise access to this variable.
69
What is * known as
What is ** known as
Dereferencing
Double-dereferencing
70
How do you find the index of a variable, for example 'b'
int *b_pointer = &b;
We use a pointer variable as addresses might be bigger or smaller than an integer.
To retrieve a value from a pointer just dereference it, for example., int b = *b_pointer
71
Why use pointers in C?
- Abstraction
- Ability to change parameter
- Multiple return values in routine
72
What is call by value?
We pass the value of variable, which means routine has a copy. Therefore, changes do not propagate back.
Example foo(v)
73
What is call by address?
We pass the address of parameter, meaning changes propagate back.
Example foo(&v)
74
What is call by address abstraction?
Manipulates objects without knowing which object in advance.
75
What is call by address swap?
A method can change the value of a thing being pointed to, without knowing what they are.
76
What is call by address efficiency?
Passing the address of start of array:
foo(&array[0])
77
Explain aspects/features of Pointer Arithmatic (Moving, incrementing, and decrementing)
(Aspect 1)
long *me
me++
++ increments the address by sizeof(*me) bytes
(Aspect 2)
Units are counted in elements being pointed to
E.g., int will increase by size(int)
(Aspect 3)
Cannot do arithmetic outside of one allocated block, but can compute (but not address)
- Explanation: It's essential to understand that this computation doesn't involve addressing new, unallocated memory. You're working within the bounds of the memory block that has been reserved for the pointer.
78
How do you find the size of an Array in C?
- Keep track yourself, or put a sentinel value at the end and count to it. (Often '\0'
79
How do we pass arrays in C?
We do NOT pass by value, instead we pass a pointer to the first object in the array.
80
Quoted strings or "string literals" are allowed or not allowed to be changed?
Where can these be used?
Not allowed.
Can be used anywhere an array can be used.
81
uint8_t integer_array[2];
uint16_t integer_array[2];
How many bytes of memory do these allocate?
- 2 Bytes
- 4 Bytes (16 bit, so 2 bytes instead of 1) and
82
What if we don't know how big an array needs to be?
We can use malloc().
For example:
uint8_t *space = malloc(16 * sizeof(uint_8);
83
We want to allocate space to store 16 unsigned 64-bit integers
uint64_t *block = malloc(sizeof(uint64_t) * 16)
84
What are some rules about free'ing memory?
When you have finished using an allocated block you must free this block.
- Never free memory you didn't allocate.
- Never free the same memory twice.
- You MUST call free before you lose the pointer to the block of memory.
85
List aspects of Structs in C
- Everything is public
- Class, without methods, no constructers, no default values
86
What is shallow copy, and what C aspects use it?
Shallow copy, ultimately copies the pointer to the thing, but not the thing itself. Therefore, a shallow copied string, will point to the same place in memory.
Struct assignment is by shallow copy:
E.g., first = second
Second points to the same location as first, but doesn't copy the value.
87
How is struct assignment done?
How is passing a struct to routines done?
How is passing a struct to routines, so that the initial value changes the passed value.
- By shallow copy
- By value
- By address
88
What do queue items hold?
A value and a pointer
89
How are structs stored
In memory together, with a name for each variable, and an 'overall' name for all the values.
90
What does a union allow in C?
Why is this important?
Union gives us multiple views of the same memory
See if the most significant or least significant digit is stored first.
91
What does the compiler, assembler and loader do?
Compiler
- Converts a high level language description of a program into an assembly code description
Assembler
- Converts assembly language into machine code
Loader
- Loads program into memory
92
How do you declare a pointer to a routine?
How to assign pointer to routine?
How to call the routine
int (*method)(int param);
- Takes param int and returns int
method = square;
result = method(6);
93
Where can pointers to routines be used?
Anywhere a variable can be used.
94
What benefits do modules provide?
- Abstraction
- Our queue (for example) could have a print method, but so could others. We can call "ob -> print()" without needing to know (exactly) which print method is called.
95
What does a constructer do for ADT structs?
Creates the object, initialises it, and sets up the function pointers.
96
What does RAII state?
Hint (C language)
"a resource is a class invariant, and is tied to the object lifetime"
Meaning, you should ONLY allocate in the constructer and deallocate only in destructor
- Allocation might be malloc(), opening a file, etc
- Deallocation might be free(), closing a file, etc.
97
Where should structs be declared?
A class(struct) declaration in C should be in .h
