CHAPTER 6: The Little Man Computer

1
CHAPTER 6The Little Man Computer

• The Architecture of Computer Hardware and Systems
  Software An Information Technology Approach
• 3rd Edition, Irv Englander
• John Wiley and Sons ?2003
• Linda Senne, Bentley College
• Wilson Wong, Bentley College

2
Introduction

• The power of the computer does not arise from
  complexity. Instead, the computer has the ability
  to perform simple operations at an extremely high
  rate of speed.
• These operations can be combined to provide the
  computer capabilities that you are familiar with.

3
LMC Little Man Computer

• Original was created by Dr. Stuart Madnick at MIT
  in 1965.
• He produced a newer version in 1979. The newer
  version has a slightly modified instruction set.
  We will use the modified version.

4
The Little Man Computer
5
Mailboxes Address vs. Content

• Addresses are consecutive
• Content may be
• Data or
• Instructions

6
Content Instructions

• Op code
• Operation code
• Arbitrary mnemonic
• Operand
• Object to be manipulated
• Data or
• Address of data

7
Magic!

• Load program into memory
• Put data into In Basket

8
Assembly Language

• Specific to a CPU
• 1 to 1 correspondence between assembly language
  instruction and binary (machine) language
  instruction
• Mnemonics (short character sequence) represent
  instructions
• Used when programmer needs precise control over
  hardware, e.g., device drivers

9
Instruction Set Direct Addressing
10
Instruction Set LOAD (Direct)
11
Instruction Set STORE (Direct)
12
Instruction Set ADD (Direct)
13
Instruction Set SUB (Direct)
14
Instruction Set INPUT
15
Instruction Set OUTPUT
16
Instruction Set HALT
17
Instruction Set SKIP
18
Instruction Set JUMP (Direct)
19
What does this program do?

• 00 IN
• 01 STA 99
• 02 IN
• 03 ADD 99
• 04 OUT
• 05 HLT
• Write the opcode.

20
What does this program do?

• 00 IN
• 01 STA 99
• 02 IN
• 03 STA 98
• 04 ADD 99
• 05 STA 97
• 06 LDA 99
• 07 OUT
• 08 LDA 98
• 09 OUT
• 10 LDA 97
• 11 OUT
• 12 HLT

21
Write a program to

• Enter two number. Find (and output) the sum of
  twice the first number plus the second number.
• Enter two number. Compute the sum of twice the
  first number and three times the second number.
  Output the first number, then the second number,
  then the result.

22
INDIRECT ADDRESSING
23
Instruction Set LOAD (Indirect)
24
Instruction Set STORE (Indirect)
25
Instruction Set ADD (Indirect)
26
Instruction Set SUB (Indirect)
27
Instruction Set JUMP (Indirect)
28
Immediate Addressing
29
Instruction Set LOAD (Immediate)
30
Instruction Set ADD (Immediate)
31
Instruction Set SUB (Immediate)
32
Indirect, Immediate, Direct

• 00 IN
• 01 STA 99
• 02 ADD 05
• 03 STA 99
• 04 ADD 99
• 05 OUT
• 06 SUB 99
• 07 OUT
• 08 HLT

33
Indirect, Immediate, Direct

• 00 IN Input a number gt 10 to the calculator
• 01 STA 99 Direct Addressing--Store data in
  calc to mailbox 99
• 02 ADD 05 Add the number five to the
  calculator
• 03 STA 99 Indirect addressing- Store
  contents of calculator
• to the mailbox pointed to by the contents
• of mailbox 99
• 04 ADD 99 Indirect addressing Add contents
  of mailbox pointed by 99 to
  contents of the calculator
• 05 OUT
• 06 SUB 99 Indirect addressing-- Subtract
  contents of mailbox pointed to by the
  contents of mailbox 99
• 07 OUT Print out result in calculator to
  output basket
• 08 HLT End program

34
Counting Forward INFINITE

• 00 LDA 90
• 01 OUT
• 02 ADD 01
• 03 STA 90
• 04 JMP 01
• 05 HLT
• 90 DAT 00

35
Counting up to an enter num

• 00 IN
• 01 STA 99
• 02 LDA 90
• 03 OUT
• 04 ADD 01
• 05 STA 90
• 06 LDA 99
• 07 SUB 01
• 08 SKN
• 09 JMP 01
• 10 HLT
• 90 DAT 00

36
LMC Input/Output
IN OUT
37
LMC Internal Data
LDA STA
38
Data storage location

• Physically identical to instruction mailbox
• Not located in instruction sequence
• Identified by DAT mnemonic

39
LMC Arithmetic Instructions
ADD SUB
40
Instruction Cycle

• Fetch Little Man finds out what instruction he
  is to execute
• Execute Little Man performs the work.

41
Fetch Portion ofFetch and Execute Cycle
1. Little Man reads the address from the location
counter
2. He walks over to the mailbox that corresponds
to the location counter
42
Fetch, cont.
3. And reads the number on the slip of paper (he
puts the slip back in case he needs to read it
again later)
43
Execute Portion
1. The Little Man goes to the mailbox address
specified in the instruction he just fetched.
2. He reads the number in that mailbox (he
remembers to replace it in case he needs it
later).
44
Execute, cont.
3. He walks over to the calculator and punches
the number in.
4. He walks over to the location counter and
clicks it, which gets him ready to fetch the next
instruction.

45
von Neumann Architecture (1945)

• Stored program concept
• Memory is addressed linearly
• Memory is addressed without regard to content