Microprocessors
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5. Immediate addressing (immediate and quick immediate).
6. Implied addressing (implied register).
13.11 32-Bit Microprocessors
This section describes the block diagram, internal architecture, salient features and instruction set of
some of the most popular 32-bit microprocessors, namely 80386 of Intel and 68020 and 68030 of
Motorola. It also gives an introduction to Intel’s 80486 and Pentium series of processors.
13.11.1 80386 Microprocessor
80386 is a 32-bit microprocessor and is the logical extension of 80286. It provides multitasking support,
memory management, pipeline architecture, address translation caches and a high-speed bus interface
in a single chip. 80386 can be operated from a 12.5, 16, 20, 25 or 33 MHz clock. The 80386 has three
processing modes, namely the protected mode, the real address mode and the virtual 8086 mode. The
protected mode is the natural 32-bit environment of the 80386 processor. In this mode, all instructions
and features are available. The real address mode is the mode of the processor immediately after
RESET. In real mode, 80386 appears to programmers as a fast 8086 with some new instructions. Most
applications of the 80386 will use the real mode for initialization only. The virtual 8086 mode (also
called the V86 mode) is a dynamic mode in the sense that the processor can switch repeatedly and
rapidly between V86 mode and protected mode.
Two versions of 80386, namely the 80386DX and the 80386SX, are commonly available. 80386SX
is a reduced bus version of the 80386. The 80386DX addresses 4 GB of memory through its 32-bit data
bus and 32-bit address bus. The 80386SX addresses 16 MB of memory with its 24-bit address bus. It
was developed after the 80386DX for applications that did not require the full 32-bit bus version. A
new version of 80386, named the 80386EX, incorporates the AT bus system, dynamic RAM controller,
programmable chip selection guide, 26 address pins, 16 data pins and 24 I/O pins. Figure 13.17 shows
the block diagram of the 80386 processor.
13.11.1.1 80386 DX registers
80386 DX contains a total of 32 registers. These registers may be grouped into general registers,
segment registers, status and instruction registers, control registers, system address registers and debug
and test registers.
13.11.1.2 Instruction Set
80386 DX executes the following instruction types:
1. Data movement instructions (general-purpose data movement instructions, stack manipulation
instructions and type conversion instructions).
2. Binary arithmetic instructions (addition and subtraction instructions, comparison and size change
instructions, multiplication instructions and division instructions).
3. Decimal arithmetic instructions (packed BCD adjustment and unpacked BCD adjustment
instructions).
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5. Immediate addressing (immediate and quick immediate).
6. Implied addressing (implied register).
13.11 32-Bit Microprocessors
This section describes the block diagram, internal architecture, salient features and instruction set of
some of the most popular 32-bit microprocessors, namely 80386 of Intel and 68020 and 68030 of
Motorola. It also gives an introduction to Intel’s 80486 and Pentium series of processors.
13.11.1 80386 Microprocessor
80386 is a 32-bit microprocessor and is the logical extension of 80286. It provides multitasking support,
memory management, pipeline architecture, address translation caches and a high-speed bus interface
in a single chip. 80386 can be operated from a 12.5, 16, 20, 25 or 33 MHz clock. The 80386 has three
processing modes, namely the protected mode, the real address mode and the virtual 8086 mode. The
protected mode is the natural 32-bit environment of the 80386 processor. In this mode, all instructions
and features are available. The real address mode is the mode of the processor immediately after
RESET. In real mode, 80386 appears to programmers as a fast 8086 with some new instructions. Most
applications of the 80386 will use the real mode for initialization only. The virtual 8086 mode (also
called the V86 mode) is a dynamic mode in the sense that the processor can switch repeatedly and
rapidly between V86 mode and protected mode.
Two versions of 80386, namely the 80386DX and the 80386SX, are commonly available. 80386SX
is a reduced bus version of the 80386. The 80386DX addresses 4 GB of memory through its 32-bit data
bus and 32-bit address bus. The 80386SX addresses 16 MB of memory with its 24-bit address bus. It
was developed after the 80386DX for applications that did not require the full 32-bit bus version. A
new version of 80386, named the 80386EX, incorporates the AT bus system, dynamic RAM controller,
programmable chip selection guide, 26 address pins, 16 data pins and 24 I/O pins. Figure 13.17 shows
the block diagram of the 80386 processor.
13.11.1.1 80386 DX registers
80386 DX contains a total of 32 registers. These registers may be grouped into general registers,
segment registers, status and instruction registers, control registers, system address registers and debug
and test registers.
13.11.1.2 Instruction Set
80386 DX executes the following instruction types:
1. Data movement instructions (general-purpose data movement instructions, stack manipulation
instructions and type conversion instructions).
2. Binary arithmetic instructions (addition and subtraction instructions, comparison and size change
instructions, multiplication instructions and division instructions).
3. Decimal arithmetic instructions (packed BCD adjustment and unpacked BCD adjustment
instructions).