Microprocessor Architecture Quiz

Microprocessor Architecture

• A microprocessor is a multipurpose, programmable logic device
• It reads binary instructions from memory
• Accepts binary data as input
• Processes data according to instructions
• Provides results as output

Basic Units of a Microprocessor

• Arithmetic Logic Unit (ALU)
• Array of registers
• Control unit

Microprocessor Applications

• General purpose applications
  • Single-board microcomputers
  • Personal computers
  • Superminis and CD-ROM drives
• Special purpose applications
  • Instrumentation
  • Control
  • Communication
  • Office automation and publication

Software and Hardware

• A program is a sequence of instructions to perform a specific function
• Hardware is the physical components of a system.
• Software is a set of programs to perform a particular task.

Assembly Language

• Assembly language uses English-like words
• It's microprocessor-specific
• Assembly language programs aren't transferable between different machines

Low-Level Language

• Low-level language uses binary (0s and 1s)
• Microprocessors understand only binary code.

High-Level Language

• High-level languages are machine-independent
• Instructions in high-level languages are known as statements
• Examples include BASIC, C, C++, and Java

Operating System

• An operating system manages the interaction between hardware and software of a computer.

Microcomputer

• A computer designed using a microprocessor as its CPU
• Includes microprocessor, memory, and I/O (Input/Output)

Advantages of Assembly Language

• Assembly language programs are compact and require less space.
• They are more efficient than high-level language programs

Advantages of High-Level Language

• High-level languages are easier to troubleshoot (debug) than assembly language programs

Microprocessor Block Diagram

• A microcomputer can be built with a microprocessor on a single chip.

Microprocessor Unit (MPU)

• An MPU includes all necessary control signals
• Some signals need to be generated by discrete components

Microprocessor Buses

• A bus is a group of conducting lines carrying data, address, and control signals.
  • Address bus
  • Data bus
  • Control bus

Address Bus (Unidirectional)

• The address bus is used by the microprocessor to identify a memory location or I/O (Input/Output) device.
• It's an output signal from the processor.

Data Bus (Bidirectional)

• The microprocessor needs to read data from memory or input devices, and write to memory or output devices.
• Therefore, a bidirectional data bus is required

ALE (Address Latch Enable) Signal in 8085

• ALE is used to demultiplex the address and data lines using an external latch
• It's an enable signal for the external latch

Multiplexing Address and Data Lines in 8085

• The data bus and low-order address bus in the 8085 are multiplexed.
• This reduces the number of pins needed.
• The hardware de-multiplexes the bus by latching the low-order address during the first T-cycle, on the falling edge of ALE

8085 Microprocessor Specifications

• 8-bit data bus
• 16-bit address bus
• Word size of 8 bits
• Memory capacity of up to 64KB

Microprocessor Significance

• The microprocessor is the master of the system
• It controls all system activity
• It fetches instructions and data from memory
• It executes instructions to perform actions

Control Section Significance

• It controls data flow within the processor.
• It receives external commands and converts them into control signals.
• It manages execution units such as ALU, data buffers, and registers.

Microprocessor Operations

• Store 8-bit data
• Perform arithmetic and logical operations
• Test conditions
• Sequence instructions
• Use memory locations for temporary data storage (stack)

Arithmetic Logic Unit (ALU)

• The ALU performs arithmetic and logic operations on 8-bit words.
• Inputs are the accumulator and temporary registers.
• Results are stored back in the accumulator.

General Purpose Registers in 8085

• 8085 has six general-purpose registers (B, C, D, E, H, L)
• Can be combined into register pairs (BC, DE, HL) to perform 16-bit operations.
• Used to temporarily store data during program execution

Flag Register Format (8085)

• Includes sign flag (SF), zero flag (ZF), auxiliary carry flag (AF), parity flag (PF), and carry flag (CY)

Flag Functions (8085)

• Sign flag (SF): Indicates the sign of the result (0 for positive, 1 for negative).
• Zero flag (ZF): Set to 1 if the result of an operation is zero; otherwise, reset.
• Auxiliary carry flag (AF): Set if a carry occurs between bits 3 and 4 during an arithmetic operation.
• Parity flag (PF): Set if the result has an even number of 1 bits; otherwise, reset.
• Carry flag (CY): Set if a carry occurs out of the most significant bit during an arithmetic operation; otherwise, reset

Accumulator

• The accumulator is the register associated with ALU operations.
• It temporarily stores the result of ALU operations
• It is often used for input/output operations

Stack

• A stack is a group of memory locations used to store binary data during program execution
• Stack instructions such as PUSH and POP are used in conjunction with the stack

Program Counter (PC)

• The program counter is a 16-bit register.
• It's used by the CPU to keep track of the address of the next instruction to be executed

Stack Pointer (SP)

• A 16-bit register used to keep track of the top of the stack.

Timing and Control

• Timing and control signal are provided by the unit for various operations.
• Controls external and internal circuits
• Operations are synchronized with a clock signal

Opcode

• The opcode is the part of an instruction that specifies the operation.
• Operands are parts of the instruction that provide additional data

IO/M signal

• Identifies if the operation is related to memory or I/O
• Low (0): Memory operation
• High (1): I/O operation

HOLD Signal

• A peripheral (such as DMA controller) requests the use of address, data, and control buses.

Interrupt Signals

• 8085 has hardware interrupts (TRAP, RST7.5, RST6.5, RST5.5, INTR) and software interrupts (RST0 through RST7).
• TRAP has the highest priority.
• There are 12 interrupts in 8085.

Additional Features of Z80

• Separate pins for data and address
• Larger instruction set
• Indexed addressing mode
• Built-in logic to refresh dynamic RAM.

Shadow Registers in Z80

• Alternate registers for each register in Z80

Common Features of 8085 and Z80

• Fabricated using NMOS technology
• 16-bit memory address, 8-bit I/O address
• Software compatible

Differences between 8085 and Z80

• 8085 uses multiplexed low-order address and data lines.
• Z80 uses separate lines for address and data.
• 8085 instruction size: 1–3 bytes
• Z80 instruction size: 1–4 bytes
• 8085 has five hardware interrupts
• Z80 has two hardware interrupts
• 8085 has 74 instructions
• Z80 has 156 instructions

Motorola 6800

• Data size: 8 bits
• Address size: 16 bits

M6800 Flags

• Negative (N)
• Zero (Z)
• Overflow (V)
• Carry (C)

Wait States

• Extra time introduced between T2 and T3 during a machine cycle.
• Used for slower peripherals or devices.

HLT Instruction

• Enters the halt state, tri-stating the buses.

Tri-state Logic

• High, low, and high-impedance states.
• High-impedance state is an open circuit condition.

One-Address Microprocessor Example

• 8085 is a one-address microprocesser