Assembly Instructions | Part 2 | Groups | AS/A Level | By ZAK

Grouping of Instruction Sets:
1. Introduction
In computer architecture, instructions are often categorized into groups based on their functionalities. This classification helps in understanding the roles these instructions play in program execution.
2. Input and Output of Data
- IN: Inputs a character and stores its ASCII value in the accumulator (ACC). This is a basic input instruction.
- OUT: Outputs the character corresponding to the ASCII value stored in ACC. This is a basic output instruction.
3. Arithmetic Operations
- ADD [address]: Adds the contents of the given memory address to ACC. It's a direct arithmetic addition.
- ADD #n/Bn/&n: Adds a constant value (`n`) to ACC. This represents immediate arithmetic addition.
- SUB [address]: Subtracts the contents of the given memory address from ACC. Direct arithmetic subtraction.
- SUB #n/Bn/&n: Subtracts a constant value (`n`) from ACC. Immediate arithmetic subtraction.
- INC [register]: Increments the contents of a register (either ACC or IX) by 1.
- DEC [register]: Decrements the contents of a register (either ACC or IX) by 1.
4. Unconditional and Conditional Instructions
- JMP [address]: Unconditionally jumps to the given memory address.
- JPE [address]: Jumps to the given address if the preceding comparison was True (equal).
- JPN [address]: Jumps to the given address if the preceding comparison was False (not equal).
5. Compare Instructions
- CMP [address]: Compares the contents of ACC with the contents at the given memory address.
- CMP #n: Compares the contents of ACC with the constant value `n`.
- CMI [address]: Indirect comparison. Compares the contents of ACC with the contents at the address located at the given address.
6. Storage Instruction
- STO [address]: Stores the contents of ACC at the specified memory address. Essential for saving computation results or transferring data.
7. Termination Instruction
- END: Returns control to the operating system, signaling the end of the program execution.
8. Conclusion
Understanding how these instructions are grouped based on their functionality is crucial for effective programming, particularly in assembly language. Each group serves a specific purpose: handling data input/output, performing arithmetic operations, controlling the flow of the program through conditional and unconditional jumps, comparing values, and managing storage. Mastery of these groups and their respective instructions is key to efficient low-level programming and system design.