Motorola M68000 Betriebsanweisung PDF herunterladen (Seite 55)

CHAPTER 4

GETTING STARTED

In order to write a program in assembly language, you must develop

a familiarity with the machine instructions of the 68000. These instruc

tions can be grouped together depending on their functions. For example,

there are instructions that are used to move data between memory and

the registers, and another group of instructions that perform the standard

arithmetic operations like addition, subtraction, multiplication, and divi

sion. Still others perform only control functions such as looping. Rather

than present all the instructions from each group in order, you will learn

some key instructions from each group so that you can start to under

stand complete programs without being overwhelmed with too many

instructions.

After you have completed this chapter you will know enough to

actually write and execute simple 68000 assembly language programs.

It is important that you take the time to experiment with your computer

system before going on to the more advanced material. Try running the

programs from this chapter as well as some of your own design. Let’s get

started.

Data Movement

Moving data between registers, and between registers and memory,

is a fundamental requirement of all programs. The 68000, like many

other microprocessors, provides a variety of machine instructions to per

form these operations. The most fundamental instruction is the move

instruction, which has the appropriate mnemonic, MOVE. There are ac

tually a number of different move instructions which all have this same

mnemonic. The assembler determines which of the actual machine in

structions is needed by a combination of an optional suffix or extension

to the mnemonic, and the types of the operands used with the MOVE

instruction. This means that we can move a constant into a register, the

contents of a memory location into a register, or a register into a register,

1 2 ... 50 51 52 53 54 55 56 57 58 59 60 ... 255 256

Keine Kommentare

Motorola M68000 Betriebsanweisung Seite 55