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• 3. Assembly Language Operations
• The Current Program Status Register
• Comparison Operations
• Branches and Conditional Execution
  • Basic Branching
  • Conditional Branches
  • Conditional Branch Instructions
  • Conditional Execution

Basic Branching

In a simple program, one instruction follows another and execution is a sequential process. The processor starts at the first instruction and works its way to the last instruction.

Frequently it will be essential for the processor to execute instructions in a different order. This might be to perform an iterative process such as a loop where the program executes a series of instruction and then returns to the start of the sequence to repeat the same set of instructions with different values. Alternatively the processor may have to make a decision, perhaps by performing a comparison operation, and on the basis of that comparison, skip over many instructions to reach a different section of the program and continue execution from the start of the new section.

This movement around a program is called branching. It is accomplished by suitable branch instructions, sometimes known as jump instructions.

The simplest branch instruction is:

The B instruction is an unconditional branch - when the processor encounters such a branch, it always jumps to the designated point. In assembly language, it is possible and desirable to represent the destination of the branch by a symbolic label. The assembler translates this label into the correct memory location, saving the programmer from having to figure out where this actually will be!