A386DX Просмотр технического описания (PDF) - Intel

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A386DX

32-BIT CHMOS MICROPROCESSOR WITH INTEGRATED MEMORY MANAGEMENT

Intel 

Intel386TM DX MICROPROCESSOR

Table 2-3 BASE and INDEX Registers for 16- and 32-Bit Addresses

16-Bit Addressing

32-Bit Addressing

BASE REGISTER

INDEX REGISTER

SCALE FACTOR

DISPLACEMENT

BX BP

SI DI

none

0 8 16 bits

Any 32-bit GP Register

Any 32-bit GP Register

Except ESP

1248

0 8 32 bits

The OPERAND LENGTH and Address Length Pre-

fixes can be applied separately or in combination to

any instruction The Address Length Prefix does not

allow addresses over 64K bytes to be accessed in

Real Mode A memory address which exceeds

FFFFH will result in a General Protection Fault An

Address Length Prefix only allows the use of the ad-

ditional Intel386 DX addressing modes

When executing 32-bit code the Intel386 DX uses

either 8- or 32-bit displacements and any register

can be used as base or index registers When exe-

cuting 16-bit code the displacements are either 8 or

16 bits and the base and index register conform to

the 80286 model Table 2-3 illustrates the differenc-

es

2 6 DATA TYPES

The Intel386 DX supports all of the data types com-

monly used in high level languages

Bit A single bit quantity

Bit Field A group of up to 32 contiguous bits

which spans a maximum of four bytes

Bit String A set of contiguous bits on the Intel386

DX bit strings can be up to 4 gigabits long

Byte A signed 8-bit quantity

Unsigned Byte An unsigned 8-bit quantity

Integer (Word) A signed 16-bit quantity

Long Integer (Double Word) A signed 32-bit quan-

tity All operations assume a 2’s complement rep-

resentation

Unsigned Integer (Word) An unsigned 16-bit

quantity

Unsigned Long Integer (Double Word) An un-

signed 32-bit quantity

Signed Quad Word A signed 64-bit quantity

Unsigned Quad Word An unsigned 64-bit quanti-

ty

Offset A 16- or 32-bit offset only quantity which

indirectly references another memory location

Pointer A full pointer which consists of a 16-bit

segment selector and either a 16- or 32-bit offset

Char A byte representation of an ASCII Alphanu-

meric or control character

String A contiguous sequence of bytes words or

dwords A string may contain between 1 byte and

4 Gbytes

BCD A byte (unpacked) representation of decimal

digits 0 – 9

Packed BCD A byte (packed) representation of

two decimal digits 0 – 9 storing one digit in each

nibble

When the Intel386 DX is coupled with an Intel387

DX Numerics Coprocessor then the following com-

mon Floating Point types are supported

Floating Point A signed 32- 64- or 80-bit real

number representation Floating point numbers

are supported by the Intel387 DX numerics co-

processor

Figure 2-10 illustrates the data types supported by

the Intel386 DX and the Intel387 DX numerics co-

processor

20

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