Module 5: Datapath

Question 1

central processing unit (CPU)

Answer 1

the electronic circuitry within a computer that carries out the instructions of a computer program by performing the basic arithmetic, logic, controlling, and input/output operations specified by those instructions; also called a central processor or main processor

Question 2

program counter (PC)

Answer 2

register in a computer processor that contains the address (location) of the instruction being executed at the current time

Question 3

ALU

Answer 3

combinational digital electronic circuit that performs arithmetic and logical operations

Question 4

Datapath

Answer 4

pathway that the data flows through in a CPU; set up by control signals specified by an instruction to the CPU

Question 5

Register file

Answer 5

contains small amount of data our processor operates on

Question 6

Control memory

Answer 6

holds control signals for our processor; essentially holds the “program” we want our CPU to execute

Question 7

TEST box

Answer 7

allows us to alter the value of the PC by testing what comes out of the ALU for a particular condition

Question 8

von Neumann model

Answer 8

computer architecture based on a 1945 description by mathematician/physicist John von Neumann and others

4 pieces:

1. processing unit (ALU + register file)
   - -performs all calculations (“overworked clerk”)
2. Memory (for instructions and data memory)
3. Control unit (contains PC)
   - -Serves as index into program memory to indicate which instruction must be carried out by the processing unit
4. Input/Output
   - -provides a means for information to be loaded into or read from the internals of the machine

Question 9

von Neumann loop

Answer 9

4 steps:

1. Fetch instructions from program memory
2. Decode instruction from program memory
3. Execute instruction in ALU (commit data to register file if needed)
4. Update program counter

–repeat loop

Question 10

Building a CPU

Answer 10

4 main pieces:

1. memory
2. data and instructions
3. PC
4. ALU

Question 11

CPU as a finite state machine

Answer 11

FSM consists of 3 basic parts:

1. an n-bit register which stores the state of the machine
   - -in our CPU this would be the memory
2. block of logic that computes the next state as a function of the current state and any inputs
   - -in our CPU this would eb the adder/subtractor (input = control memory)
3. block of logic which computes the output based on the current state
   - -not yet in the CPU (but we will have it soon!)

Question 12

NZP Tester

Answer 12

Two internal parts to the TEST component

1. determine if incoming # is negative/zero/positive
2. compare incoming condition from user to output of part 1