5. Processor fundamentals Flashcards
What buses does the system bus contain?
System bus contains the data, address and control buses
What 2 kinds of registers are there?
Registers can be either general purpose or special purpose and for simplicity purposes we say that there is one general purpose register which we call - the accumulator.
What are CIR, IX, MAR, MDR, PC, SR registers?
CIR - current instruction register. Stores the current instruction while it is being decoded and executed.
IX - index register. Stores a value; only used for indexed addressing.
MAR - memory address register. Stores the address of a memory location which is about to have a value read from or written to.
MDR - Memory data register. Stores data that has just been read from memory or is just about to be written to memory.
PC - Program counter. Stores the address of where the next instruction is to be read from.
SR - status register. For the status register each individual bit is used as a logical flag for a specific type of interrupt or problem that has occured. The bit is set to 1 if a condition is detected and 0 otherwise.
What is the function of address bus?
The sole function of the address bus is to carry an address
What is the function of a data bus?
The function of the data bus is to carry data. This might be an instruction, an address or a value.
What is the function of control bus?
Control bus carries control signals from the processor to other components. The control bus also carries the clock’s pulses.
Describe the F-E cycle.
• The address in the program counter is the address of next item to be fetched
• The address is copied into MAR
• Using the address bus the instruction from that address moved/copied from main memory to MDR with the data bus
• The instruction is transferred from MDR to CIR
• Instruction is decoded in the CIR into op code and operand
• The processor executes the instruction.
• The address in PC is incremented ready for next loop
What is the purpose of CU?
CU (Control Unit) is responsible for controlling the flow of data and that program instructions are handled correctly.
What is the purpose of ALU?
ALU (Arithmetic and Logic Unit) is responsible for the arithmetic and logic processing
