Chapter 4 Flashcards

Question

What can cause interrupts?

Answer 1

o Timing signal o Input/output processes (e.g. disk drive ready to receive more data) o Hardware fault (e.g.: paper jam, out of paper) o User interaction (e.g.: Ctrl+Alt+Break keys to interrupt a process) o Software error (e.g.: .exe not found, division by zero)

Answer 2

1. At the end of each fetch–execute cycle the processor checks for interrupt(s) 2. Checks if an interrupt flag/bit is set (in interrupt register). 3. Processor identifies source of interrupt 4. Checks the priority of interrupt. 5. If the interrupt priority is high enough - Processor saves current contents of registers and - Calls interrupt handler / Interrupt Service Routine (ISR) - Address of ISR is loaded into Program Counter (PC) - When servicing of interrupt complete, processor restores registers 6. Lower priority interrupts are re-enabled 7. Processor continues with next F–E cycle

Answer 3

A bus is a set of parallel wires connecting two or more components of the computer

Answer 4

Carries signal relating to addresses of main memory locations or input/output device to be used between the processor and memory Unidirectional (addresses travel in one direction only) – from the processor to MAR

Answer 5

``` Sends data between the processor, the memory unit (and the input/output devices) ``` Bi-directional (data can travel in both directions). Data is carried from CPU to memory (and vice versa) as well as to and from input/output devices

Answer 6

Carries signals relating to the control and coordination of all activities within the computer (e.g.: read and write functions) from CU to all the other computer components Bi-directional. It carries signals from the CU to all the other computer components

Answer 7

The wider the data bus, the larger the number of bits (word length) that can be transported simultaneously at one time. Increasing the width of address bus increases the performance of a computer system as fewer transfers are needed (increases the performance of a computer system)

Answer 8

``` ▪ Clock cycle/speed ▪ Width of the address bus and data bus ▪ Overclocking ▪ Cache memory ▪ Number of cores ```

Answer 9

• Clock speed can be changed by accessing the BIOS. • But, clock speed higher than that the computer was designed for can lead to: - Instruction is unable to complete in time before the next one is due to be executed → unsynchronised operations - Serious overheating of CPU → unreliable performance

Answer 10

* A type of high-speed RAM which is built into the CPU – faster access times * Holds the most frequently used instructions and data for faster access

Answer 11

* Dual core or quad core * Doubling the number of cores does not imply improvement of computer performance b/c CPU needs to communicate with each core → reduces overall performance

Answer 12

▪ I/O devices are connected to computer via ports ▪ Interaction of the ports with the I/O devices is controlled by the CU ▪ Most common types of ports (on modern computers) o USB ports o HDMI o VGA

Answer 13

▪ An asynchronous serial data transmission method ▪ The standard method for transferring data between a computer and a number of devices ▪ Essentially, the USB cable consists of a four-wire shielded cable: - two for power and the earth - two used in the data transmission

Answer 14

Devices plugged into the computer are automatically detected: device drivers are automatically uploaded The connectors can only fit one way; this prevents incorrect connections being made Has become the industry standard; considerable support is available to the users Several different transmission rates are supported Newer USB standards are backward compatible with older USB standards USB 3.0 allows full duplex data transfer Allows power to be drawn to charge portable devices

Answer 15

Present transmission rate is limited (less than 500 Mbps) Maximum cable length is about 5 metres The older USB standard (e.g. 1.1) may not be supported in the near future

Answer 16

▪ HDMI ports allow output (audio & visual) from a computer to an HDMI–enabled device ▪ Support high definition signals ▪ Replaced VGA

Answer 17

▪ Analogue technology | ▪ Supports 640x480 pixels

Answer 18

Standard for modern televisions and monitors Very fast data transfer rate Improved security Supports modern digital systems

Answer 19

Easy to break connection when moving Limited cable length to retain good signal 5 cable/connection standards

Answer 20

Simpler technology Only 1 standard available Easy to split signal and connect a number of devices from 1 source Secure connection

Answer 21

Out-dated Easy to bend the pins when connecting Cables must be of high quality to ensure good signal

Answer 22

▪ CPU only uses machine code, which is binary (sometimes displayed on screen as hex) ▪ Each different computer type has its own set of machine code instructions ▪ Each machine code instruction performs a single task, e.g.: storing a value in a specified memory location ▪ Writing machine code: - Time consuming - Error prone

Answer 23

▪ Low-level machine specific programming language that uses mnemonics ▪ Structure of assembly – each instruction has: - Opcode (operation code): identifies the operation to be carried out by the CPU - Operand: identifies the data to be used by the opcode (not all instructions have this)

Answer 24

* It translates each assembly language instruction into a machine code instruction * It checks the syntax of assembly language – ensuring that only opcodes of the appropriate machine code instruction set are used

Answer 25

1. Single Pass Assemblers | 2. Two Pass Assemblers

Answer 26

▪ Puts the machine code instructions straight into the computer memory to be executed

Answer 27

▪ Produces an object program in machine code that can be stored, loaded and executed at a later stage ▪ The source program is scanned twice, so that labels in assembly can be replaced with memory addresses in machine code

Answer 28

!A symbol table is created (labels are added to the table along with the address, if the address is known)! * Read the assembly language program one line at a time * Ignore anything not required (ex comments) * Allocate a memory address for the line of code * Check the opcode is in the instruction set * Add any new labels to the symbol table with the address, if known * Place address of labelled instruction in the symbol table

Answer 29

!An instruction (/opcode/mnemonic) table is created! * Read the assembly language program one line at a time * Generate object code, including opcode and operand, from the symbol table generated in Pass 1 * Save or execute the program

Answer 30

``` ▪ Comments ▪ Symbolic names for constants ▪ Labels for addresses ▪ Macros ▪ Subroutines ▪ Directives ▪ System calls ```

Answer 31

▪ A group of instructions given a name (// subroutine) ▪ Need to be executed several times within the same program ▪ The statements are written once and called using the name whenever they need to be executed. ▪ Macro code is inserted into the source file at each place it is called

Answer 32

1: Defining a macro: - The definition of a macro consists of three parts: the header, body, and terminator MACRO The header . . . . The body: instructions to be executed ENDM The terminator 2: Invoking a macro by using its given on a separate line followed by the list of parameters used if any: [parameter list]

Answer 33

▪ An instruction that directs the assembler to do something ▪ Not a program instruction; It is information for the assemble ▪ Instructs the assembler as to how it should construct the final executable machine code: directing how memory should be used or defining files or procedures that will be used

Answer 34

▪ Some tell the assembler to set aside space for variables ▪ Others tell the assembler to include an external source files ▪ Others establish the start address for your program

Answer 35

▪ Assembler instruction generates machine code ▪ Assembler directive does not create machine code: it directs the assembler to perform certain actions during assembly phase.

Answer 36

1. Data movement 2. Input and output of data 3. Arithmetic operations 4. Unconditional & conditional instructions 5. Compare

Answer 37

``` ▪ Allow data stored at one location to be copied into the accumulator ▪ LDM ▪ LDD ▪ LDI ▪ LDX ▪ LDR ▪ MOV ▪ STO ▪ END ```

Answer 38

▪ Allow data to be read from the keyboard or output to the screen ▪ IN ▪ OUT ** No opcode

Answer 39

``` ▪ Perform simple calculations on data stored in the accumulator and store the answer in accumulator (overwriting the original data) ▪ ADD ▪ SUB ▪ INC ▪ DEC ```

Answer 40

▪ JMP ▪ JPE ▪ JPN ▪ END

Answer 41

▪ CMP | ▪ CMI

Answer 42

``` ▪ Absolute addressing ▪ Direct addressing ▪ Indirect addressing ▪ Indexed addressing ▪ Immediate addressing ▪ Relative addressing ▪ Symbolic addressing ```

Answer 43

▪ The operand refers directly to a memory location

Answer 44

▪ The contents of the contents of the memory location in the operand are used

Answer 45

▪ The operand is used to form an address: operand + the contents of the Index Register (IX)

Answer 46

▪ The operand is the actual value to be loaded

Answer 47

▪ The operand is added to the base address (current address) to give the actual address

Answer 48

▪ The operand is a label that represents the memory location

Answer 49

▪ Logical left shift moves each bit in a word one/more bit position(s) to the left. ▪ Zeros are introduced on the right-hand end ▪ A left shift moves the bits to more significant positions (like multiplying by two) !Does not preserve the sign of the word (positive or negative)!

Answer 50

▪ Logical right shift moves each bit in a word one/more bit position(s) to the right. ▪ Zeros are introduced on the left-hand end ▪ A right shift moves them to less significant positions (like dividing by two) !Does not preserve the sign of the word (positive or negative)!

Answer 51

▪ They can be used for dividing or multiplying an integer variable

Answer 52

▪ The digits dropped off at one end of a word are returned at the other end of the word (in a circle/loop) ▪ No bits are lost

Answer 53

▪ LSL n -> n places to the left ▪ LSR n -> n places to the right ▪ Shifts are always performed on the ACC

Answer 54

▪ In monitoring and control, each bit in a register or memory location can be used as a flag and would need to be tested, set or cleared separately Example: act as sensors to detect when data has been processed ▪ Represented by 1 bit ➔ 8-bit register ▪ The instructions: - AND used to check if the bit has been set - OR used to set the bit - XOR used to clear a bit that has been set

Answer 55

▪ A bitmask is a way of accessing a particular bit ▪ The bitmask is a number which has 0 in all bits that we don’t care about, and a 1 for the bit(s) that we want to examine ▪ By ANDing the bitmask with the original number, we can “extract” the bit(s)