Khaled A. Al-Utaibi

 Computers are Every Where  What is Computer Engineering?  Design Levels  Computer Engineering Fields  What is a Microcomputer ?  Course Objectives  The Stored Program Concept  The Stored Program Processing Cycle  Three-Bus System Architecture  The 80x86 Family

 Microcomputer systems are becoming an essential part of any product or equipment in all fields including − House Appliances − Office Equipment − Telecommunications − Transportation − Traffic Control − Medical Equipment − Industrial Control

 Work

 A microcomputer is an electronic device with a microprocessor as its central processing unit (CPU), a memory, and input/output (I/O) facilities.

 When a microcomputer is equipped with a keyboard and screen for input and output and is running an operating system (DOS, Windows, Linux, etc) it is called a personal computer.

 To introduce the fundamental hardware and software concepts needed for the design of microcomputers system.

− Functions of various processor pins − Memory/IO Read and Write bus cycles − Main types of memory technology − Memory internal organization − Design memory interfaces. − Computer serial and parallel interfaces

 To introduce the fundamental hardware and software concepts needed for the design of microcomputers system. − How interrupts are used to implement I/O control and data transfers − Design interrupt service routines and I/O drivers using assembly language. − Data access from magnetic and optical disk drives using DMA − Types of bus interfaces in a computer system

 Most of today’s computer systems are based on a design principle proposed by Dr. John Von Neumann (1946).

 The basic stored program computer (Von Neumann Architecture) consists of three major parts: (1) CPU, (2) Memory, (3) I/O Devices.

 The basic stored program cycle consists of three major steps: (1) Fetch, (2) Decode, (3) Execute.

 Clock Generator: − Controls the basic timing of the computer − It generates a square wave signal − This signal is used to synchronize all activities within the computer  Registers: − Two types (general purpose, special purpose) − General purpose registers are used to store temporary information − Special purpose registers are used for specific tasks (e.g. the accumulator)

 Fetching, Decoding and Executing an Instruction: − The basic processing cycle begins with a memory fetch or read cycle − The Instruction Pointer (IP) holds the address of next instruction to be fetched. − This address is output on the system address bus. − The memory address decoder examines the binary value of the address on the system address bus and selects the proper memory location.

 Fetching, Decoding and Executing an Instruction: − The CPU activate the memory read control through the system control bus. − This causes the selected data byte (i.e. instruction) in the memory to be placed onto the data bus. − The instruction is then placed in the Instruction Register (IR). − Once in the CPU, the instruction is decoded and executed. − When executing the instruction is completed, the cycle is repeated.

 The Instruction Set: − The job of the Instruction Decoder (ID) is to recognize and activate appropriate controls in the CPU needed to execute the instruction. − The list of all instructions recognized by the ID is called the instruction set. − Microprocessors are classified based on the specification of the instruction sets into two categories:  (1) Complex Instruction Set Computers (CISC) and  (2) Reduced Instruction Set Computers (RISC)

 Modern CPUs: − Most microprocessors today are designed to allow the fetch and execute cycles to overlap. − This is done by dividing the CPU into two units:  (1) a Bus Interface Unit (BIU) and  (2) an Execution Unit (EU). − The job of the BIU is to fetch instructions from memory and store them in a special instruction queue. − The EU then fetches instructions from this queue (not from memory). − Some processors have a pipelined execution unit that allows the decoding and execution of instructions to overlap.

 A bus is a collection of electronic signal lines all dedicated to a particular task.  The architecture considered in the previous slides consists of three types of buses: address, data, and control buses.

 The Data Bus: − The data bus consists of internal and external data buses. − The internal data bus connects the internal components of the CPU (e.g. Registers, ALU, etc.) to the data I/O pins of the CPU. − The external data bus connects the data I/O pins of the CPU to the memory and I/O devices (e.g. printer, monitor, etc). − The width of the internal data bus in bits is usually used to classify a microprocessor (e.g. 8-bit, 16-bit, 32-bi microprocessors)

 The Data Bus: − The width of the internal data bus is usually the same as the external data bust – but not always. − The processor has 32-bit internal and 32-bit external data buses. − The 80386SX processor has 32-bit internal data bus, but 16-bit external data bus. − The Pentium processor has 32-bit internal data bus and 64-bit external data bus.

 Memory Banks: − How a 64-bit (or 32-bit or 16-bit) processor can access an 8-bit-wide memory? − The memory is divided into banks. − The 8086 processor (16-bit) requires 2 banks (16/8=2).

 Memory Banks: − How a 64-bit (or 32-bit or 16-bit) processor can access an 8-bit-wide memory? − The memory is divided into banks. − The processor (32-bit) requires 4 banks (32/8=4).

 The address Bus: − It is used to identify the memory location or I/O device (also called I/O port) to be accessed by the CPU − The width of this bus in the 80x86 family varies from one processor to the other for example:  The 8086/8088 processors have 20-bit address bus.  The processor has 24-bit address bus.  The 80386/80486/Pentium processors have 32-bit address bus.  The Pentium Pro processor has 36-bit address bus.

 Example 1: How many different memory addresses can an 8086 output? Repeat for and processors.

 Example 1: How many different memory addresses can an 8086 output? Repeat for and processors. − 8086 processor has 20 address lines − Addressable memory locations = 2 20 = 1M − processor has 24 address lines − Addressable memory locations = 2 24 = 2 4 x2 20 = 16M − processor has 32 address lines − Addressable memory locations = 2 32 = 2 2 x2 30 = 4G

 The Control Bus: − How can we tell if the address on the address bus is a memory address or an I/O port ? − How can we tell if the memory or I/O access is a read or write operation ? − These questions are answered by the control bus. − Each time the processor outputs an address, it also activates one of 4 control signals  (1) Memory Read  (2) Memory Write  (3) I/O Read  (4) I/O Write

 The 8086 Microprocessor (1978): − 20-bit address bus. − 16-bit internal data bus. − 16-bit external data bus. − Separate bus interface unit (BIU) and execution unit (EU). − 16-bit registers (with the ability to access the high or low 8 bits separately). − Built in hardware multiply and divide instructions. − Support for an external floating-point math coprocessor.

 The 8088 Microprocessor (1979): − 20-bit address bus. − 16-bit internal data bus. − 8-bit external data bus. − Separate bus interface unit (BIU) and execution unit (EU). − 16-bit registers (with the ability to access the high or low 8 bits separately). − Built in hardware multiply and divide instructions. − Support for an external floating-point math coprocessor.

 The & Microprocessors (1982): − A personal computer (PC) based on the 8086/8088 microprocessors requires several additional chips such as: a clock generator, a programmable timer, a programmable interrupt controller, a direct memory access controller and a circuitry to select the I/O devices. − To simplify the design, Intel introduced the & microprocessors. − The 80186/80188 integrates on a single chip an 8086/8088 microprocessor and all the chips mentioned above. − The & are often referred to as high- integration processors − Used as a microcontroller

 The Microprocessor (1982): − 24-bit address bus. − 16-bit internal data bus. − 16-bit external data bus. − Designed to be software compatible with 8086 & microprocessors. − Provides two programming modes:  Real Mode  Protected Mode

 The Microprocessor (Real Mode): − The processor function exactly like the 8086 processor. − That is, any 8086 program can be run on a Real Mode processor without any change. − The processor uses only its 20 least significant address lines. − So, the memory space is limited to 1 MB.

 The Microprocessor (Protected Mode): − In this mode, the processor supports a multiprogram environment. − It gives each program a predetermined amount of memory. − This uses the full memory space which is 16MB. − This mode is called Protected Mode because several programs can be loaded into memory at once (each in its own segment), but are protected from each other.

 The Microprocessor (1984): − 32-bit address bus. − 32-bit internal data bus. − 32-bit external data bus. − 32-bit registers. − Provides three modes:  Real Mode (identical to that of 80286)  Protected Mode (manages 4 GB of memory in a way similar to that of the 80286).  Virtual Mode (similar to Real Mode, except that multiple 8086 processors can run simultaneously

 The Microprocessor (1989): − 32-bit address bus. − 32-bit internal and external data bus. − 32-bit registers. − On-chip cache (stores the most recently used instructions and data ) − Integrated Floating-Point Unit (FPU) − Real & Protected Modes as in − Pipelined design

 The Pentium Microprocessor (1993): − 32-bit address bus. − 32-bit internal − 64-bit external data bus. − 32-bit registers. − Two instructions pipelines − On-chip cache − Integrated FPU