computer science

• a small device that contaibs all components of a computer
• e.g. microwave, washing machine, satnav, camera

pros of embedded system - 

• physically small
• less power - cheaper to run
• less power - no overheating
• efficient
• easy to replace - built on single printed circuit

Data Bus - carries binary data around computer

Address Bus - carries address of memory locations used to store data

Control Bus - sends and recieves signals that controls components + CPU

• fetches memory from RAM
• fetch-execute-decide cycle
• purpose is to process data

The Control Unit - 

• controls the way data moves around the CPU
• Controls + monitors flow of data between CPU and input / output devices
• Executes instructions provided by program

The Arithmetic Logic Unit ( ALU ) -

• performs arithmetic operations
• logic operations / comparisons
• shift operations

Registers - 

• type of memory
• temporarily holds data while software is running
• faster than RAM and Cache
• inside CPU

• both data and software being used are stored in RAM
• task can be changed by loading different program into memory

Features of Von Neumann Layout - 

• RAM has enough memory for both data and program ds - easy to load different program
• control unit handles movement of data and instructions
• info and instructions carried by buses
• ALU in charge of Arithmetic and Logic Operations
• way of inputting and outputting data

Memory Address Register ( MAR ) -

• every instruction is in a specific location
• each location has a unique address
• address being accessed is temporarily stored in MAR
• address passed to RAM via Address Bus

Memory Data Register ( MDR ) -

• data must be stored in MDR for it to be fetched from RAM
• data can travel both ways ( unlike instructions )
• can be fetched from RAM to be decoded by CPU
• after processing it can be sent back to RAM to be temporarily stored
• all data must pass through the MDR via data bus

Program Counter ( PC ) -

• points to instruction currently being executed
• as each instruction is processed, PC is updated with address of next instuction to fetch
• PC copies info to MAR and increments

Accumulator -

• Temporarily stores ALU's results
• makes it simpler to write software that handles data
• program runs faster - registers are faster than RAM

Current Instruction Register ( CIR ) -

• holds the instruction that is currently being decoded and executed

step 1 -   address in PC ( 305 ) is copied to MAR

step 2 -   address in MAR is passed onto Address Bus and Control Unit sends a signal to RAM                 to read this address

step 3 -   instruction at 305 is sent across Data Bus and copied into MDR, then the MDR is                      copied into the Instruction Register. The PC is then incremented

step 4 -   instruction's decoded by Control Unit, so CPU knows what to do.Various parts of the                  CPU are prepared for the next stage

step 5 -   the decoded instructions performed. and the PC is already pointing to the next                            intstruction

step 6 -   cycle restarts