microprocessors - 80386dx

UNIT 1Microprocessors

What is a Microprocessor?

Also called as the Brain of the computer. It is an integrated circuit that incorporates

all the functions of the Central Processing unit (CPU)

It is used to perform various arithmetic and logical operations, stores data and controls the system.

In 1971, Intel introduced first microprocessor Intel 4004 which was able to perform processing, transmit data and apply simple mathematical operations.

Smart phones, washing machines, microwave also have microprocessors.

Basic Architecture of a Microprocessor

Accumulator

Timing and clock

circuit Program Counter

Stack Pointer

ALU

Interrupt Circuit

Working Registers

Basic Architecture of a Microprocessor ALU(Arithmetic and Logic Unit): - used to perform arithmetical(+,-,*,/) and

logical(and,or,ex-or,not,ex-nor) operation. Accumulator: - It is used to store the result of the ALU. Registers: - It is used to store data. - Registers are classified into: >General Purpose Registers >Temporary Registers >Special purpose Registers

Basic Architecture of a Microprocessor Interrupt Control: - It accepts different types of interrupt

request input. For a valid interrupt request it takes the necessary actions.

Timing and Control Unit: - It provides timing signal(Clock cycles). - It provides control signals to the system. Buses: - The different types of buses are: >Data bus: To carry data >Address bus: To send address of memory

locations >Control bus: To carry control signals (eg.

Read/write)

Arithmetic and Logical Unit

ALUInput

Operands

Opcode

Output Operand

Definitions Opcode: Operation that is to be

performed in operands. Operands: data on which operations are

to be performed. Instruction: combination of opcode and

operands to instruct a system. Instruction set: a set of instructions that

can be issued to a system. Program/Subroutine/Procedure: Set of

instructions written in a particular order.

Definitions Interrupt: It is a mechanism by which an

I/O device(h/w interrupt) or an instruction(s/w interrupt) can suspend the normal execution of the processor and get itself serviced.

Interrupt service routine(ISR): A small program or a routine that when executed services the corresponding interrupting source is called as an ISR.

Definitions Vectored/Non-Vectored interrupt: If the

ISR address of the interrupt is to be taken from the interrupting source itself, then it is called as non-vectored interrupt; otherwise it is a vectored interrupt.

Maskable/Non-maskable interrupt: Interrept that can be masked(disabled) and unmasked(enabled) by the programmer is called as maskable interrupt else it is a non-maskable interrupt.

Types of Microprocessor: There are basically 3 types of

microprocessors:• Complex Instruction Set

Microprocessors.- consists instruction that perform complex tasks.- requires large amount of time to execute instructions.

• Reduced Instruction Set Microprocessors.- work with simple instructions.- requires less amount of time for execution.

• Superscalar Microprocessors.- perform number of tasks at the same time.

Application of Microprocessors: Microcomputers Personal Computers Printing Machines Security Systems Play Stations Digital Projectors Washing Machines Microwave Ovens

Evolution of Microprocessor: 4-bit microprocessor

- In 1971, Intel Corp. introduced 4-bit microprocessor 4004.- It had a single chip that can perform arithmetic and logical operations on 4-bit data.

8-bit microprocessor- In 1973, Intel introduced 8-bit microprocessor 8008,8085.- It can perform arithmetic and logical operations on 4,8 bit data.

16-bit microprocessor- Intel 8086 and 80286.- can perform arithmetic and logical operations on 4,8 and 16 bit data.

Evolution of Microprocessor: 32-bit microprocessor:

- Intel 80386.- Performs arithmetic and logical operations on 4,8,16 and 32 bit data.

64-bit microprocessor: - Intel Pentium.

- Performs arithmetic and logical operations on 4,8,16 and 32 bit data.

80386 Microprocessor It is a 32-bit microprocessor. It has 32-bit registers. ALU can operate on 8/16/32 bit data

operands. It supports physical address of 4GB. It supports virtual address of 64TB. It operates in 3 different modes : real,

protected and virtual mode. The memory management unit provides

virtual memory, paging and segmentation, 4 level of protection.

Clock frequency: 20,25, and 35MHz (Clock cycles/second)

80386 Microprocessor 80386 is categorized as:

- 80386SX(16bit data bus,24bit address bus, 32bit registers)- 80386SL(16bit data bus,24bit address bus, 32bit registers in addition to bus controller, memory controller, cache controller)- 80386DX(16/32bit data bus,32bit address bus, 32bit registers)- 80386EX(80386DX(16/32bit data bus,32bit address bus, 32bit registers)

Types of Memory Cache Memory Primary Memory Secondary Memory

Cache Memory- Cache memory is a extremely high speed memory that can speed up CPU operation.- It is used to access data/instructions that are most regularly used by CPU.- Quick access to these data/instructions will speed up the software program.- It stores data for temporary use.

Primary Memory- RAM(Random Access Memory) accesses memory locations randomly.- Volatile memory – means data will be lost when power is off.- Faster than secondary memory.- Two types of RAM:

> Static RAM (SRAM) > Dynamic RAM (DRAM)

SRAM Vs DRAMSRAM (Static RAM) DRAM (Dynamic

RAM)SRAM uses flip flops DRAM uses

capacitors.No refreshing required

Continuous refreshing required to retain data

Faster data access Slower access to dataMore space as more number of components required.

Less space as less number of components are required.

Costly CheaperUsed as Cache memory

Used as Main Memory

Secondary Memory- ROM (Read Only Memory) - Non-volatile memory- retains data- cheaper than RAM - eg. Hard disks, CD/DVD etc.

Secondary MemoryTypes of ROM: > PROM (programmable read only

memory) - written only once, cannot be re-

written.> EPROM (Erasable programmable ROM) - can be erased with UV Rays and can be re-written. > EEPROM ( Electronically Erasable PROM) - can be erased with an electrical beam.

Architecture of 80386DX

Architecture of 80386DX Architecture of 80386DX is divided into:

- Central Processing Unit (CPU)- Memory Management Unit (MMU)- Bus Interface Unit (BIU)

Architecture of 80386DX

Central Processing Unit Central Processing Unit has:

- Execution Unit- Instruction Unit

Task of CPU is to fetch instruction, decode it and execute the given instruction.

Execution Unit Execution Unit has: - 8 general purpose registers

- 8 special purpose registers - These registers will be used either

to store data or calculate offset addresses.- Execution unit is used to execute instructions from Instruction unit.

Instruction Unit Instruction unit has:

- Prefetch unit- Decode unit

Instruction Prefetch unit is used to fetch instructions in advance. It will store next instructions to be executed in prefetch queue.

Instruction Decode unit is used to decode the prefetched instruction and will store the decoded instruction in Decoded instruction queue.

Central Processing Unit When Execution unit is executing the

current instruction the prefetch unit fetches the next 16B instructions and stores in it Prefetch queue.

The execution of program needs arithmetic and logical operations performed by the ALU.

Operands for the ALU come from the Register File – General Purpose registers.

Execution unit has 32 bit flag register used to give the status of the result.

Protection test unit gives protection to programs based on their privileges.

Memory Management Unit Memory Management unit consists of:

- Segmentation Unit- Paging Unit

Segmentation unit: - divides memory into different segments.- maximum segment size is of 4GB.

Paging unit:- divides memory in terms of pages. - Page size is 4KB- works under control of segmentation unit. i.e. segments are divided into pages.

Bus Interface Unit Bus Interface unit has:

- Request Prioritizer: resolve the priorities of various bus request. It will control the access to a bus.- Address Driver: provides addresses- Pipeline and transreceiver will receive different instructions and store it in pipeline.

Register Organization Memory locations inside the processor

are nothing but the registers. There are two types of registers:

- User registers: used for user applications.- System registers: used by the operating system.

Register Organization of 80386

General Purpose Registers It holds the operands of an instruction on

which operation is to be performed. 80386 has 8 32-bit registers that can be

used as either 8/16/32 bit registers. 32-bit registers are known as extended

registers. (prefix E) EAX,EBX,ECX,EDX,EBP,ESP,ESI and EDI

are general purpose registers.

Segment registers These are 16-bit registers that hold the

base address of a segment:- CS: Base address of code segment- DS: Base address of data segment- ES,FS,GS: Base address of data segment- SS: Base address of stack segment.

Instruction Pointer and Flag Register EIP:

- 32-bit register that contains memory offset of the next instruction.

Flag register:- 32-bit flag register is used to give the status of the result of the operation performed by the ALU.

Flag register

Flag register Carry flag (CF):

- 1 if operation results in a carry.- 0 otherwise

Parity flag (PF):- 1 if result contains even number of 1’s- 0 otherwise

Auxilliary Flag (AF):- 1 if there is a carry from 3rd bit to 4th bit- 0 otherwise

Flag register Zero flag (ZF)

- 1 is result is 0- 0 otherwise

Sign Flag (SF)- 1 is result of the operation is negative- 0 otherwise

Trap Flag (TF)- 1 if it operates in single step mode. - 0 otherwise

Flag register Interrupt enabled Flag (IF):

- 1 means interrupts from devices are allowed- 0 means interrupts are ignored

Direction Flag (DF):- 1 means it is a string operation- 0 otherwise

Input/Output Privilege level (IOPL):- 2 bit field to set privilege to the instructions to be executed.

Flag register Nested Flag (NF):

- 1 means current instruction is a nested instruction- 0 otherwise

Resume Flag (RF):- 1 at starting execution of every instruction.- 0 no execution

Virtual mode Flag (VM):- 1 processor operating in virtual mode- 0 normal mode

System Registers Segment Descriptor registers:

- stores information about the segments. Control Registers: CR0,CR2,CR3

- control overall system operations. System address registers:

- stores address of descriptor tables Debug and Test registers: DR0-DR7

- used when debugging programs.

Operating Modes in 80386 Protected Mode Real Address Mode Virtual Address Mode

Machine Cycle Fetch

- get instruction from the memory Decode

- interpret/understand the instruction Execute

- execute/run the instruction Store

- store result of the execution

Signal in 80386 CLK: provides clock timing to the processor D0-D31: data transmission A2-A31: address transmission Ready: indicates previous cycle is finished and

ready for next cycle VCC: power supply ERROR: error in execution INTR: interrupt request INTA: interrupt acknowledgement NMI: non-maskable interrupt Reset: reset processor settings