Little Man Computer

LMC Instruction Set

Note that in the following table 'xx' refers to a memory address (aka mailbox) in the RAM. The LMC has 100 different mailboxes in the RAM ranging from 00 to 99.

Mnemonic	Name	Description	Op Code
INP	INPUT	Retrieve user input and stores it in the accumulator.	901
OUT	OUTPUT	Output the value stored in the accumulator.	902
LDA	LOAD	Load the Accumulator with the contents of the memory address given.	5xx
STA	STORE	Store the value in the Accumulator in the memory address given.	3xx
ADD	ADD	Add the contents of the memory address to the Accumulator	1xx
SUB	SUBTRACT	Subtract the contents of the memory address from the Accumulator	2xx
BRP	BRANCH IF POSITIVE	Branch/Jump to the address given if the Accumulator is zero or positive.	8xx
BRZ	BRANCH IF ZERO	Branch/Jump to the address given if the Accumulator is zero.	7xx
BRA	BRANCH ALWAYS	Branch/Jump to the address given.	6xx
HLT	HALT	Stop the code	000
DAT	DATA LOCATION	Used to associate a label to a free memory address. An optional value can also be used to be stored at the memory address.

Little Man Computer (LMC) Simulators

• QcO's LMC Simulator : Source code at GitHub
• LMC Simulator Applet
• Tiny-Dude : Source code at GitHub
• LMC Simulator Applet (offline)

ProgrammingNaming Conventions

To make your code more readable, you can use the following naming conventions:

• For instructions use All Caps
• For labels ,variables and constants use camelCase
• Prefix labels with lb e.g. lbLoop INP
• Prefix variables with var e.g. varSum DAT 0
• Prefix constants with val e.g. valOne DAT 0

Mini Challenges / Examples

1. Write a program that loads and outputs the value 10.
2. Write a program that adds two inputs together and outputs the result.
3. Write a program that adds three inputs together and outputs the result.
4. Write a program that takes two inputs and subtracts the second from the first.
5. A program that outputs the larger of two input values.
6. A program that outputs the larger of three input values.
7. A program that takes three inputs and Outputs them in ascending order.
8. A program that takes two inputs and subtracts the second from the first. If the result is negative, the program should subtract the first input from the second.
9. A program that counts down from any input value.
10. A program that outputs the product of two input values.
11. A program that outputs the quotient of two input values.
12. A program that outputs the remainder of two input values.

Challenges

1. Write a program to ...

2. Write a program to count the sum of descending numbers from an input down to 1. e.g.

   $$f(n) = n + (n - 1) + (n - 2) + ... + 3 + 2 + 1\\\ f(5) = 5 + 4 + 3 + 2 + 1$$

   solution

3. Write a program to count the number of inputs. solution