NOTICE:

Examples

(Clicking an example will replace any code inside the assembly code box)

• Adding two numbers
• Subtracting a number
• Multiplying two numbers
• Dividing a number

LMC Instruction Set

The LMC has nine instructions. Each instruction has an assembly mnemonic that is equivalent to a three-digit (decimal) instruction. In this numerical instruction, the first digit usually represents the instruction, and the second and third digits usually represent a mailbox address.

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 accumulator 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 accumulator 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 accumulator (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 - BRP
numerical/machine code - 8
If the contents of the accumulator (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 accumulator (calculator) to the given address. Note: since the program is stored in memory, data and program instructions all have the same address/location format.

DATA LOCATION

mnemonic - DAT
numerical/machine code - (the data)
When compiled, a program converts each instruction into a three-digit code. These codes are placed in sequential mailboxes. Instead of a program component, this instruction will reserve the next mailbox for data storage.