Microprocessor Theory and Applications with 68000/68020 and Pentium

6

ASSEMBLY LANGUAGE PROGRAMMING WITH THE 68000

In this chapter we describe the fundamental concepts associated with assembly language programming using the Motorola 68000 microprocessor. Topics include 68000 registers, addressing modes, instruction sets, and assembly language programming.

6.1 Introduction

The 68000 is Motorola's first 16-bit microprocessor. Its address and data registers are all 32 bits wide, and its ALU is 16 bits wide. The 68000 requires a single 5-V supply. The processor can be operated from a maximum internal clock frequency of 25 MHz. The 68000 is available in several frequencies, including 4, 6, 8, 10, 12.5, 16.67, and 25 MHz. The 68000 does not have on-chip clock circuitry and therefore, requires an external crystal oscillator or clock generator/driver circuit.

The 68000 has several different versions, which include the 68008, 68010, and 68012. The 68000 and 68010 are packaged either in a 64-pin DIP (dual in-line package) with all pins assigned or in a 68-pin quad pack or PGA (pin grid array) with some unused pins. The 68000 is also packaged in 68-terminal chip carrier. The 68008 is packed in a 48-pin dual in-line package, whereas the 68012 is packed in an 84-pin grid array. The 68008 provides the basic 68000 capabilities with inexpensive packaging. It has an 8-bit data bus, which facilitates the interfacing of this chip to inexpensive 8-bit peripheral chips. The 68010 provides hardware-based virtual memory support and efficient looping instructions. Like ...