1. The CPU

2. Parts of the CPU Control Unit Arithmetic & Logic Unit Registers

3. Control Unit Send out the signals to fetch instructions from memory. Interpret those instructions Send out signals to enable instructions to be carried out. This is known as the fetch execute cycle

4. Arithmetic & Logic Unit Carries out arithmetic calculations Carries out logic operations (AND/OR)

5. Registers Temporary storage locations in processor itself Store data during calculations Store the address of the next instruction to be executed Hold the instruction as it is being decoded and executed

6. Registers Program Counter (PC) - Stores the memory address of the next program instruction Instruction Register (IR) - Holds the code for the current instruction Accumulator (ACC) - Holds values before and after processing by the ALU Memory Data Register (MDR) - Holds data prior to a memory write or after a memory read. Memory Address Register (MAR) - Holds the address of the memory location to be accessed.

7. Buses Address Bus Data Bus Control Bus Other internal buses which transfer data inside the CPU

8. Address Bus used by the processor to pinpoint the memory location, needed this is a one-way bus.

9. Data Bus used to transfer the data its size will usually match the word size i.e. the size of the memory locations this is a two-way bus.

10. Control Bus initiates and controls whatever process is taking place Read Line – initiates memory read operation. Write Line - initiates memory write operation. Clock – Generates pulse to synchronise components. Interrupt – Signal to processor of an interrupt like a key press or mouse click. Processor saves stack and deals with the interrupt. NMI – Non-Maskable Interrupt. Interrupt which cannot be ignored. Reset – Clears all registers, aborts program and gives control back to the operating system.

11. The Fetch Execute Cycle In Action Click on the next slide to show the next step

12. 1101 2256 3241 4506 5 6 7 8 9 10 PCIR MDR MAR ACC Control Unit READ LINE WRITE LINE Arithmetic Logic Unit 1 1 101 2 Address Bus Data Bus The program counter is copied into the MARThe read control line is activated The contents of memory is transferred to the MDR Add one to the program counterCopy contents of MDR to IRDecode the instructionExecute the instruction