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Little Man Computer

Little Man Computer. When your program gets “translated to machine code” all 0’s & 1’s The translator must know the language of the program (java) as well as the language of the cpu – “the instruction set” LMC is a simple instruction set for “toy” computer. About The LMC.

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Little Man Computer

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  1. Little Man Computer • When your program gets “translated to machine code” all 0’s & 1’s • The translator must know the language of the program (java) as well as the language of the cpu – “the instruction set” • LMC is a simple instruction set for “toy” computer

  2. About The LMC • It is a model/illustration of a computer • Created by Dr. Stuart Madnick at MIT in 1965 (he updated it in 1979) • A fairly accurate representation of how computers still work today.

  3. Calculations and other operations performed by: CPU (Central Processing Unit)

  4. LMC Model

  5. 789 456 LMC Schematic 00 123 123 01 500 02 199 03 500 04 399 05 95 96 97 98 99 123 05

  6. 789 456 System Counterparts ALU Input/output interface 00 123 123 01 500 02 199 03 500 04 399 05 Control unit 95 96 97 98 99 123 05 Program counter

  7. System Block Diagram CPU Memory ALU Input/outputinterface Control unit Program counter

  8. LMC Instruction Set • Layout of Instructions • 3 digits (use decimal; idea is similar in binary) • Think of memory as storage locations – mailboxes that can hold one slip of paper with 3 digits

  9. LMC Instruction Set • Interpretation of the 3 digit • 1st digit = instruction called the operation code op code for short • 2nd and 3rd digits mailbox address (for the most part) • eg. • 225 means “store into mailbox 25”

  10. LMC Instruction Set

  11. LMC Instruction Set

  12. LMS Instruction Set

  13. LMS Instruction Set

  14. A program to add 2 numbers 00 500 input 01 299 store data 02 500 input 03 399 add 04 600 output 05 700 stop 99 data

  15. A program to find positive difference of 2 numbers 00 Input 500 01 Store 11 211 02 Input 500 03 Store 12 212 04 Subtract 11 411 05 Skp if Neg 800 06 Jmp 09 909 07 Load 11 111 08 Subtract 12 412 09 Output 600 10 Halt 700 11 Data 000 12 Data 000

  16. Fetch, (Decode,) Execute Instruction Cycle • Fetch: get the next instruction as indicated by the program counter: goes to mbox address and reads the 3 digit code (the instruction) and then increments the program counter • Decode: electronically decode the instruction to determine which operation to perform (not shown in LMC) • Execute: perform the instruction • Repeat cycle until halt

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