MC68030 View Datasheet(PDF) - Motorola => Freescale

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Description

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MC68030

ENHANCED 32-BIT MICROPROCESSOR

Motorola => Freescale 

Data Organization and Addressing Capabilities

2.2.2 Address Registers

Each address register and stack pointer is 32 bits wide and holds a 32-bit address. Address

registers cannot be used for byte-sized operands. Therefore, when an address register is

used as a source operand, either the low-order word or the entire long-word operand is

used, depending upon the operation size. When an address register is used as the

destination operand, the entire register is affected, regardless of the operation size. If the

source operand is a word size, it is first sign-extended to 32 bits and then used in the

operation to an address register destination. Address registers are used primarily for

addresses and to support address computation. The instruction set includes instructions

that add to, subtract from, compare, and move the contents of address registers. The

following example shows the organization of addresses in address registers.

31

Sign-Extended

16

15

0

16-Bit Address Operand

31

0

Full 32-Bit Address Operand

Address Organization in Address Registers

2.2.3 Control Registers

The control registers described in this section contain control information for supervisor

functions and vary in size. With the exception of the user portion of the status register (CCR),

they are accessed only by instructions at the supervisor privilege level.

The status register (SR), shown in Figure 1–4, is 16 bits wide. Only 12 bits of the status

register are defined; all undefined values are reserved by Motorola for future definition. The

undefined bits are read as zeros and should be written as zeros for future compatibility. The

lower byte of the status register is the CCR. Operations to the CCR can be performed at the

supervisor or user privilege level. All operations to the status register and CCR are word-

sized operations, but for all CCR operations, the upper byte is read as all zeros and is

ignored when written, regardless of privilege level.

2-4

MC68030 USER’S MANUAL

MOTOROLA

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