CPU Simulator Documentation

Architecture Overview

The CPU simulator implements a simple 16-bit architecture with the following features:

• 16-bit word size
• 256 words of memory
• Program Counter (PC)
• Accumulator (ACC)
• Instruction Register (IR)
• Zero and Carry flags

Instruction Set

Instruction	Opcode	Description
HALT	0x0	Stop program execution
LOAD value	0x1	Load immediate value into ACC
LOADM addr	0x2	Load value from memory into ACC
STORE addr	0x3	Store ACC to memory
ADD value	0x4	Add immediate value to ACC
ADDM addr	0x5	Add memory value to ACC
SUB value	0x6	Subtract immediate value from ACC
SUBM addr	0x7	Subtract memory value from ACC
JUMP addr	0x8	Jump to address
JUMPZ addr	0x9	Jump if ACC is zero
JUMPNZ addr	0xA	Jump if ACC is not zero

Example Programs

Counter Program

; Count from 0 to 255
LOAD 0        ; Initialize counter
loop:
    STORE 100  ; Store current value
    ADD 1      ; Increment
    JUMPNZ loop; Continue if not zero
HALT

Memory Copy Program

; Copy memory from address 50 to 100
LOAD 10       ; Number of values to copy
STORE 0       ; Store counter
loop:
    LOADM 50   ; Load from source
    STORE 100  ; Store to destination
    LOAD 1
    ADD 50     ; Increment source address
    STORE 50
    LOAD 1
    ADD 100    ; Increment destination address
    STORE 100
    LOADM 0    ; Load counter
    SUB 1      ; Decrement counter
    STORE 0    ; Store updated counter
    JUMPNZ loop; Continue if counter not zero
HALT

Assembly Syntax

• One instruction per line
• Labels end with a colon (label:)
• Comments start with semicolon (; comment)
• Numbers can be decimal or hexadecimal (prefix with 0x)
• Instructions and labels are case-insensitive

Memory Layout

The memory consists of 256 16-bit words (addresses 0-255). There are no reserved memory locations, and the program can use any memory address for data storage.

• Word Size: 16 bits
• Memory Size: 256 words
• Address Range: 0x000 to 0x0FF
• Instruction Format: 4-bit opcode + 12-bit operand