MOTOROLA
M68000 8-/16-/32-BIT MICROPROCESSOR USER’S MANUAL
2-1
SECTION 2
INTRODUCTION
The section provide a brief introduction to the M68000 microprocessors (MPUs).
Detailed information on the programming model, data types, addressing modes, data
organization and instruction set can be found in M68000PM/AD, M68000 Programmer's
Reference Manual. All the processors are identical from the programmer's viewpoint,
except that the MC68000 can directly access 16 Mbytes (24-bit address) and the
MC68008 can directly access 1 Mbyte (20-bit address on 48-pin version or 22-bit
address on 52-pin version). The MC68010, which also uses a 24-bit address, has much
in common with the other devices; however, it supports additional instructions and
registers and provides full virtual machine/memory capability. Unless noted, all
information pertains to all the M68000 MPUs.
2.1
PROGRAMMER'S MODEL
All the microprocessors executes instructions in one of two modes—user mode or
supervisor mode. The user mode provides the execution environment for the majority of
application programs. The supervisor mode, which allows some additional instructions
and privileges, is used by the operating system and other system software.
2.1.1 User' Programmer's Model
The user programmer's model (see Figure 2-1) is common to all M68000 MPUs. The
user programmer's model, contains 16, 32-bit, general-purpose registers (D0–D7, A0–
A7), a 32-bit program counter, and an 8-bit condition code register. The first eight
registers (D0–D7) are used as data registers for byte (8-bit), word (16-bit), and long-word
(32-bit) operations. The second set of seven registers (A0–A6) and the user stack pointer
(USP) can be used as software stack pointers and base address registers. In addition,
the address registers can be used for word and long-word operations. All of the 16
registers can be used as index registers.