Digital Electronics: Principles, Devices and Applications

Microprocessors 5515. Immediate addressing (immediate and quick immediate).6. Implied addressing (implied register).13.11 32-Bit MicroprocessorsThis section describes the block diagram, internal architecture, salient features and instruction set ofsome of the most popular 32-bit microprocessors, namely 80386 of Intel and 68020 and 68030 ofMotorola. It also gives an introduction to Intel’s 80486 and Pentium series of processors.13.11.1 80386 Microprocessor80386 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 interfacein a single chip. 80386 can be operated from a 12.5, 16, 20, 25 or 33 MHz clock. The 80386 has threeprocessing modes, namely the protected mode, the real address mode and the virtual 8086 mode. Theprotected mode is the natural 32-bit environment of the 80386 processor. In this mode, all instructionsand features are available. The real address mode is the mode of the processor immediately afterRESET. In real mode, 80386 appears to programmers as a fast 8086 with some new instructions. Mostapplications of the 80386 will use the real mode for initialization only. The virtual 8086 mode (alsocalled the V86 mode) is a dynamic mode in the sense that the processor can switch repeatedly andrapidly between V86 mode and protected mode.Two versions of 80386, namely the 80386DX and the 80386SX, are commonly available. 80386SXis a reduced bus version of the 80386. The 80386DX addresses 4 GB of memory through its 32-bit databus and 32-bit address bus. The 80386SX addresses 16 MB of memory with its 24-bit address bus. Itwas developed after the 80386DX for applications that did not require the full 32-bit bus version. Anew 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 showsthe block diagram of the 80386 processor.13.11.1.1 80386 DX registers80386 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 debugand test registers.13.11.1.2 Instruction Set80386 DX executes the following instruction types:1. Data movement instructions (general-purpose data movement instructions, stack manipulationinstructions and type conversion instructions).2. Binary arithmetic instructions (addition and subtraction instructions, comparison and size changeinstructions, multiplication instructions and division instructions).3. Decimal arithmetic instructions (packed BCD adjustment and unpacked BCD adjustmentinstructions).