1.1.1: Structure and Function of the Processor
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What does the Arithmetic Logic Unit do to the data?
• Performs arithmetic and logical operations on the data
What instructions can the Arithmetic Logic Unit do?
• ADD • SUBTRACT • MULTIPLY • DIVIDE • On fixed or floating point numbers
What operations can the Arithmetic Logic Unit do?
• Shift operations comparing two values • Using AND, OR, NOT, XOR
What does the Control Unit do?
• Controls and coordinates the activities of the CPU • Directs the flow of data between CPU and other devices
What does the Control Unit do to the next instruction?
• Accepts the next instruction • Decodes it into several sequential steps [e.g. fetching addresses and data from memory] • Manages its execution • Stores the resulting data back in memory or registers
What are Registers?
• A small amount of very high speed memory • Used to temporarily store data, and all arithmetic, logical, and shift operations
What is the purpose of the Program Counter?
• Holds address of the next instruction to be executed
What is the purpose of the Accumulator?
• Stores results from calculations
What is the purpose of the Memory Address Register?
• Holds address of a location that is to be read from or written to
What is the purpose of the Memory Data Register?
• Temporarily stores data that has been read or data that needs to be written
What is the purpose of the Current Instruction Register?
• Holds the current instruction being executed, divided up into operand and opcode
What are Buses?
• A set of parallel wires connecting two or more components inside the CPU
What is the width of a Bus?
• The number of parallel wires the bus has • Typically 8, 16, 32, or 64 wires wide
What is the width of a Bus directly proportional to?
• Directly proportional to the number of bits that can be transferred simultaneously at any given time
What is the Data Bus?
• Bi-directional bus used for transporting data and instructions between components
What is the Address Bus?
• Uni-directional bus used to transmit the memory addresses specifying where data is to be sent to or retrieved from
What is the width of the Address Bus proportional to?
• The number of addressable memory locations
What is the Control Bus?
• Bi-directional bus used to transmit Control Signals between internal and external components
What does the Control Bus do?
• Coordinates the use of Address and Data Busses • Provides status information between system components
What does the Control Signal ‘Bus Request’ do?
• Shows that a device is requesting the use of the Data Bus
What does the Control Signal ‘Bus Grant’ do?
• Shows that the CPU has granted access to the Data Bus
What does the Control Signal ‘Memory Write’ do?
• Data is written into the addressed location using this bus
What does the Control Signal ‘Memory Read’ do?
• Data is read from a specific location to be placed onto the Data Bus
What does the Control Signal ‘Interrupt Request’ do?
• Shows that a device is requesting access to the CPU