Introduction to 80386DX Basic

Introduction to 80386DX Basic

  7:29 AM    Dnyaneshwar Kudande

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                                 1.  80386DX-Basic Programming Model

1.1 Evolution of Processor:

Processor	Introduction	Data Bus	Address Bus	Memory
4004	1971	4	8	256 Byte
8008	1972	8	8	256 Byte
8080	1974	8	16	64KB
8086/88	1978	16/8	20	1MB
80186	1982	16/8	20	1MB
80286	1983	16	24	16MB:Clock speed is high
80386	1986 DX(1986:not compatibility) SX(1988: mostly used, Not Co-Processor)	DX:32+132 pin SX:16+100 pin	32 24	DX:4GB (275,000 transistor) SX:16MB
80486		32	32	Memory Size: 4GB+16K cache

1.2  Difference between 80286, 80386 and 80486:

1.3  Difference between 80386 SX/DX

•         Both have the same internal architecture.

•         Lower cost package and the ease of interfacing to   8-bit and 16-bit memory and peripherals make ,

•         SX suitable for use in low cost systems.

1.4  Introduction to 80386

·         The 80386 is an advanced 32-bit microprocessor optimized for multitasking operating systems and designed for applications needing very high performance.

·         The 32-bit registers and data paths support 32-bit addresses and data types.

·         The processor can address up to 4 gigabytes of physical memory and 64 terabytes (246 bytes) of virtual memory.

·         The on-chip memory management facilities include address translation registers, advanced multitasking hardware, a protection mechanism, and paged virtual memory.

·         Special debugging registers provide data and code breakpoints even in ROM-based software.

1.5  Features of 80386

The 80386 has three processing modes:

1. Protected Mode: 

o   Protected mode is the natural 32-bit environment of the 80386 processor.

o   In this mode all instructions and features are available.

2. Real-Address Mode.

o   Real-address mode is the mode of the processor immediate after RESET.

o   In real mode the 80386 appears to programmers as a fast 8086 with some new instructions.

o   Most applications of the 80386 will use real mode.

3. Virtual 8086 Mode:

o   Virtual 8086 mode is a dynamic mode which can switch repeatedly and rapidly between V86 mode and protected mode.

o   The CPU enters V86 mode from protected then leaves V86 mode and enters protected.

1.6  Internal Architecture

Figure.1: Internal Architecture of 80386DX

ž     The Internal Architecture of 80386 is divided into 3 sections:

—  i) Central processing unit (CPU)

○     Execution unit (EU) and

○     Instruction unit (IU)

—  ii) Memory management unit (MMU)  

○     Segmentation unit

○      Paging unit.

—  iii) Bus interface unit( BIU)