The Little Man Computer

Instruction cycle (fetch) Read address from Location Counter; Walk to address 3. Read content

Instruction cycle (execute LOAD 1/2) 1. Go to mailbox specified by instruction 2. Read content

Instruction cycle (execute LOAD 2/2) 3. Go to calculator and punch content 4. Increment LC

Input/output interface System Block Diagram CPU Highest Address Memory Lowest ALU Input/output interface Control unit Program counter

The Little Man Computer

Generic CPU With Registers Program Counter ( PC ) Instruction Register ( IR ) Memory Memory Address Register ( MAR ) Memory Data Register ( MDR ) Accumulator ( A or Acc )

Memory address register Memory Unit n bits Memory cell bit 0 1 2 3 4 2n-1 bit 1 Memory address register Address decoder bit n - 1 0 1 2 m - 1 Memory data register m bits p. 160

MAR-MDR example

A visual analogy for memory