An open-source assembly simulator based on LMC (Little Man Computer), aimed to teach students basic assembly programming in a user-friendly virtual computer model environment.

The Instruction Set

Core Components:

• Memory: the computer's memory
• Registers:
  • IR (Instruction Register): holds the instruction to be executed
  • MAR (Memory Address Register): holds the current address that is being used for a read/write operation
  • MBR (Memory Buffer Register): holds data that is going to be written into a memory address
  • PC (Program Counter): holds the index of the current executing instruction
• Accumulator: holds a number, used for performing arithmetic operations
  

Additional Components:

• Graphics Screen: displays each memory chunk as a color, being able to read and process the data in different color formats (RGB565, RGB555, RGB444 and etc.)

Memory Handling Mechanism:

There are some ways LDC differentiates from the basic LMC - each memory chunk (or mailbox) has a storage of 2 bytes. The instructions are stored in the following way, considering the decimal format: starting from the left-hand side, the first three digits are used for storing the operand, while the rest of the two digits are used to store the opcode. An operand has a range of [-999; 999] and the opcode has a range of [0-31]. This allows for there to be 32 unique instructions (and an additional instruction without an opcode), due to the nature of short (16-bit) integers.