Data Organization And Addressing Capabilities; Instruction Operands; Memory Management Unit - Motorola MC68030 User Manual

SECTION 2
DATA ORGANIZATION AND ADDRESSING
CAPABILITIES
Most external references to memory by a microprocessor are either program references or
data references; they either access instruction words or operands (data items) for an
instruction. Program references are references to the program space, the section of memory
that contains the program instructions and any immediate data operands that reside in the
instruction stream. Refer to M68000PM/AD, M68000 Programmer's Reference Manual , for
descriptions of the instructions in the program space. Data references refer to the data
space, the section of memory that contains the program data. Data items in the instruction
stream can be accessed with the program counter relative addressing modes, and these
accesses are classified as program references. A third type of external reference used for
coprocessor communications, interrupt acknowledge cycles, and breakpoint acknowledge
cycles is classified as a CPU space reference. The MC68030 automatically sets the function
codes to access the program space, the data space, or the CPU space for special functions
as required. The function codes can be used by the memory management unit to organize
separate program (read only) and data (read-write) memory areas.
This section describes the data organization and addressing capabilities of the MC68030. It
lists the types of operands used by instructions and describes the registers and their use as
operands. Next, the section describes the organization of data in memory and the
addressing modes available to access data in memory. Last, the section describes the
system stack and user program stacks and queues.

2.1 INSTRUCTION OPERANDS

The MC68030 supports a general-purpose set of operands to serve the requirements of a
large range of applications. Operands of MC68030 instructions may reside in registers, in
memory, or within the instructions themselves. An instruction operand might also reside in
a coprocessor. An operand may be a single bit, a bit field of from 1 to 32 bits in length, a byte
(8 bits), a word (16 bits), a long word (32 bits), or a quad word (64 bits). The operand size
for each instruction is either explicitly encoded in the instruction or implicitly defined by the
instruction operation. Coprocessors are designed to support special computation models
that require very specific but widely varying data operand types and sizes. Hence,
coprocessor instructions can specify operands of any size.
MOTOROLA MC68030 USER'S MANUAL 2-1