Assembly Language — common mistakes

You are not expected to memorise the binary opcodes for instructions. The exam will always provide the necessary instruction set. Your task is to understand what each instruction does and be able to trace the execution of a program step-by-step, tracking the contents of registers (ACC, IX) and memory.

Learning assembly language provides a fundamental understanding of computer architecture. It reveals how the CPU, memory, and registers work together. This knowledge is crucial for performance-critical applications like device drivers, embedded systems, and real-time computing, where direct hardware control is necessary.

No, it is not. Assembly language is architecture-specific. An assembly program written for an Intel x86 processor will not run on an ARM processor (found in most smartphones) because they have different instruction sets, registers, and architectures. This is why assembly language is not considered 'portable'.

The opcode (operation code) is the instruction itself—it tells the CPU what to do (e.g., ADD, LDR, JMP). The operand is the data or memory address that the instruction operates on—it tells the CPU what to do it with (e.g., the value #5 or the address 250).

A two-pass assembler reads the assembly code twice. It's needed to handle 'forward references'—when an instruction jumps to a label that hasn't been defined yet. On the first pass, it builds a symbol table of all labels and their addresses. On the second pass, it uses this completed table to translate all instructions, including the forward jumps, into machine code.