Microprocessor Systems: Fundamentals

Microprocessor Systems

• Microprocessors are widely used, replacing hardware-based logic designs with software-controlled flexibility.
• This shift allows for easy modification of system characteristics through software changes.
• New applications have emerged because of the microprocessor's cost-effectiveness compared to minicomputers and complex hardware logic.

Fundamentals of Microprocessors

• Microprocessors are programmable, multipurpose, clock-driven, and register-based electronic devices.
• They read binary instructions from memory, accept binary data as input, process the data, and output results.

Learning Objectives

• After reading this, students should discuss the birth, basic principles, and operation of microprocessors.
• Describe the principle of microprocessor systems

Technical Skills

• One must be familiar with logic circuits and switching theory.

Duration

• Topic 1, "The Fundamentals of Microprocessor," requires 4.5 hours.
• Topic 2, "Memory Mapping Format of a Microprocessor," needs 3.0 hours.

Computer Types

• Mainframe computers: Large, room-sized machines.
• Minicomputers: Smaller than mainframes, fitting in a large filing cabinet, cheaper, and operable in regular rooms.
• Microcomputers: Resulted from the advent of microprocessors in 1971, small and used in various applications.
• Personal computers: General-purpose computers with microprocessors.

Microprocessor Origins

• Automatic machine control initially used TTL logic circuitry. Sequential operations used flip-flops and counters. Process conditions used combinational logic.
• The minicomputer's introduction enabled computer-controlled machinery and industrial processes.
• In 1971, an engineer conceived designing logic where circuit sequences were program-stored, leading to the microprocessor.

Core Components

• Microprocessor systems consist of the Arithmetic and Logic Unit (ALU), registers, and buses.

Definitions

• ALU: Circuitry for arithmetic and logical operations (ADD, SUBTRACT, AND, OR, SHIFT).
• Registers: Temporary internal storage, typically holding 8 or 16-bit operands.
• Bus: Parallel wires (metallization or conductive silicon) conveying information.

The ALU

• In practice, one input operand (1 byte) goes into a special register known as an ACCUMULATOR, so the result of one addition can be carried forward to the next. Here, the result is stored in the accumulator, overwriting any previous data. It derives its name from this accumulating action.
• A typical sequence adds two 8-bit numbers by loading the accumulator with operand A, fetching operand B, adding them, and storing the result in the accumulator.
• ALUs require function select inputs for diverse operations beyond adding or ANDing.
• The 74HC181 is a 4 + 4 bits ALU with 32 programmable functions.

General Microprocessor

• Providing data words at inputs, storing output words, and giving function codes are needed to make an ALU a processor.
• An 8-bit microprocessor handles larger words in 8-bit chunks.

Microprocessor Function

• Registers and the ALU connect via a DATA BUS, enabling data transfer for operations.
• Timing and control circuits manage which device uses the data bus at a time.
• Instead of private connections, devices share wires, using time multiplexing.

Buses

• Besides the 8-bit data bus, a 16-bit address bus exists, controlled by signals.
• A microprocessor has limited internal data storage.

Memory

• External memory can be read and written to using the internal data bus.
• Buffers manage external memory chips.

Data Bus

• The data bus is bidirectional to transfer data to and from external memory.
• A control signal, READ/NOT-WRITE (R/W), dictates data direction. HIGH signals a memory read; LOW indicates a memory write.
• The address bus carries a 16-bit code that identifies external memory cells.
• The settings of the R/W line dictates each memory location's response to its code and its data direction.
• The address bus is unidirectional because the microprocessor usually generates addresses. 65536 external bytes of data can be accessed by the address bus of 8-bit microprocessors (16-bits wide).

Registers

• Data Registers: These are registers that carry out arithmetic and logical instructions.
• Address Registers: Addresses stored in them can be manipulated. Used for data movement instructions
• Program Counter: Tracks the processor's location in a program..
• Instruction Register: Holds the binary instruction word while it's being executed.
• Temporary Registers: used to hold transitory data while an instruction is being carried out

Buses: Essential Data Pathways

• Buses enable data transfer between components of a computer system.
• To transfer 8 bits, 8 wires or PCB tracks are normally used for these.

Buses: Function and Types

• Address Bus: Connects the processor to memory and interfaces. Used to show which memory or interface register is sending or getting data (16 bits in 6809).
• Data Bus: Transfers data between the processor, memory, and interfaces but must prevent scrambling by allowing only one device to place data on the bus at a time; the 6809 system's data bus has 8 bits.

Summary of Microprocessor Systems

• The ALU executes logical and arithmetic operations
• ALUs are often connected with accumulators, making it easier to perform logical and arithmetic operations on their contents.
• Registers can execute certain ways that allow them to perform specific operations inside the computer
• Timing and control circuits coordinate data transfers in order.
• The ALU, the timing circuits process data and transfer data back and forth in a matter of nanoseconds.
• Address and Data Busses are in place to transfer data within and outside the microprocessor.

Memory Mapping

• Memory mapping translates between logical address space and physical memory.
• Memory mapping goals include logical-to-physical address translation, memory protection, and memory resource management.
• Memory mapping impacts computer performance via instruction execution time and program run time.
• Each time a program displays a logical memory address, the translation mechanism must translate that address into the appropriate physical memory location.

Little-Endian

• With little-endian hardware, the lowest byte of a multi-byte scalar gets stored at the lowest memory address. Intel/AMD x86, Digital VAX, and Digital Alpha use this format.

Big-Endian

• With big-endian setups, the most significant byte of a multi-byte number is stored "first," meaning at the lowest memory address. IBM mainframes, Motorola 680x0, Sun SPARC, PowerPC, and most RISC machines use this format.

Integer Storage

• With big-endian storage, the highest, most significant byte of a multi-byte scalar is stored "first" in the lowest memory address.
• Conversely, with "little-endian," the lowest, least significant byte is stored initially in the lowest address.
• Considering 0x44332211, with "little-endian, is 0x11; the two memory storage patterns are 104 11, 103 22, 102 33, 101 44