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Little Man Computer

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The Little Man Computer (LMC) was created by Dr. Stuart Madnick. The LMC models a simple von Neumann architecture computer, so it has all of the basic features of a modern computer. The LMC can be programmed in machine or assembly code, and the following simulator will allow you to run your programs.

LMC Commands

LOAD mnemonic - LDA numerical/machine code - 5

Load the contents of the given mailbox onto the accumulator (calculator). Note: the contents of the mailbox are not changed.


STORE mnemonic - STA numerical/machine code - 3

Store the contents of the accumulator (calculator) to the mailbox of the given address. Note: the contents of the accumlator are not changed.


ADD mnemonic - ADD numerical/machine code - 1

Add the contents of the given mailbox onto the accumulator (calculator). Note: the contents of the mailbox are not changed, and the actions of the accumulator are not defined for add instructions that cause sums larger than 3 digits.


SUBTRACT mnemonic - SUB numerical/machine code - 2

Subtract the contents of the given mailbox from the accumulator (calculator). Note: the contents of the mailbox are not changed, and the actions of the accumulator are not defined for subtract instructions that cause negative results -- however, a negative flag will be set so that BRP can be used properly (see below).


INPUT mnemonic - INP numerical/machine code - 901

Copy the value from the "in box" onto the accumulator (calculator).


OUTPUT mnemonic - OUT numerical/machine code - 902

Copy the value from the accumulator (calculator) to the "out box". Note: the contents of the accumlator are not changed.


END mnemonic - HLT numerical/machine code - 000

Causes the Little Man Computer to stop executing your program.


BRANCH IF ZERO mnemonic - BRZ numerical/machine code - 7

If the contents of the accululator (calculator) are 000, the PC (program counter) will be set to the given address. Note: since the program is stored in memory, data and program instructions all have the same address/location format.


BRANCH IF ZERO OR POSITIVE mnemonic - BRZ numerical/machine code - 8

If the contents of the accululator (calculator) are 000 or positive (i.e. the negative flag is not set), the PC (program counter) will be set to the given address. Note: since the program is stored in memory, data and program instructions all have the same address/location format.


BRANCH ALWAYS mnemonic - BRA numerical/machine code - 6

Set the contents of the accululator (calculator) to the given address. Note: since the program is stored in memory, data and program instructions all have the same address/location format.

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