The Microprocessor

CHAPTER 7Load and Store Operations

About this chapter

In the previous two chapters, we looked at arithmetic and logic instructions, which handle all the computing work required in a program. These instructions always operate on the registers, whereas the actual data in the program resides in memory. In this chapter, we will explore the instructions that allow us to transfer data between registers and memory.

What do we learn?

• What is alignment?
• What is endianness?
• What are basic load and store instructions?
• How do load and store instructions manage different data types?
• How does offset addressing work?
• What is a literal pool?

As in the previous chapters, we will write code snippets to deepen our understanding.

7.1 INTRODUCTION

As we learnt in the previous two chapters, computing operations are performed on the registers, while the actual data in the program resides in the memory. Therefore, the processor needs the capability to load data from the memory into its registers and store the computed data back into the memory. Cortex-M0, with its 32-bit data bus and 32-bit registers, can transfer a byte, a 16-bit half-word, or a 32-bit word in a single instruction. Accordingly, the instruction set includes instructions to load or store a byte, half-word and a word.

Figure 7.1 Byte, half-word and word stored at address A.

Figure 7.1 shows a byte, half-word and a ...