8085 Microprocessor Architecture

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Questions and Answers

What is the primary advantage of the 8085 microprocessor over its predecessor 8080?

  • Higher operational clock speed
  • Ability to perform 16-bit operations
  • Ability to address up to 64KB (correct)
  • Advanced interrupt handling mechanism

Which of the following is NOT a feature of the 8085 microprocessor?

  • It has a 16-bit address bus (correct)
  • It is compatible with NMOS technology
  • It requires a +5V power supply
  • It operates at 3.2 MHz single-phase CLK

In the context of 8085 microprocessor operations, what does the term 'Machine Cycles' refer to?

  • The states of memory access during data transfer processes
  • The various types of bus transfers occurring in microprocessor tasks
  • The duration of time a microprocessor takes to execute a particular command (correct)
  • The sequence of operations a processor performs in a single instruction

Which component is specifically used for interfacing programmable devices with the 8085 microprocessor?

<p>Programmable Peripheral Interface (PPI) (C)</p> Signup and view all the answers

What is the maximum addressing capability of 8085 microprocessor?

<p>64KB (C)</p> Signup and view all the answers

What type of data bus does the 8085 microprocessor utilize?

<p>8-bit data bus (A)</p> Signup and view all the answers

Which of the following instructions are NOT part of the instruction set of 8051 microcontroller?

<p>String manipulation instructions (A)</p> Signup and view all the answers

What distinguishes the usage of Memory Mapped I/O from I/O Mapped I/O in the context of the 8085?

<p>Memory-mapped I/O uses dedicated address space while I/O mapped does not (B)</p> Signup and view all the answers

Which interrupt has the highest priority in the 8085 microprocessor?

<p>TRAP (B)</p> Signup and view all the answers

What type of addressing mode involves providing the operand explicitly within the instruction?

<p>Immediate Addressing Mode (C)</p> Signup and view all the answers

Which of the following is NOT a type of machine cycle in the Intel 8085 microprocessor?

<p>Data Transfer Cycle (B)</p> Signup and view all the answers

Which signal condition does the microprocessor verify while executing an instruction when INTR = 1?

<p>The condition of the INTR signal (A)</p> Signup and view all the answers

Which of the following applications is NOT typically associated with the 8085 microprocessor?

<p>Smartphones (B)</p> Signup and view all the answers

What does the execution of the RST 6.5 interrupt entail in the 8085 microprocessor?

<p>Storage of PC data into the stack and addresses to 0034H (D)</p> Signup and view all the answers

Which of the following bus timings identifies the stable period of the address during a machine cycle?

<p>T1 (D)</p> Signup and view all the answers

What will happen to the INTR signal when the microprocessor is in RESET state?

<p>INTR moves to a disabled state (A)</p> Signup and view all the answers

Which addressing mode is characterized by the address of the operand being placed in a register?

<p>Register Addressing Mode (D)</p> Signup and view all the answers

Which of the following control signals does NOT manage the direction of data flow in the 8085 microprocessor?

<p>PC (C)</p> Signup and view all the answers

In which application is the 8085 microprocessor NOT commonly used?

<p>Smart thermostats (A)</p> Signup and view all the answers

Which machine cycle is responsible for fetching data from memory for processing?

<p>Memory Read Cycle (B)</p> Signup and view all the answers

What is the primary function of the SID and SOD signals in the 8085 microprocessor?

<p>Serial interfacing (D)</p> Signup and view all the answers

Which component of the 8085 microprocessor is primarily responsible for managing data flow and execution of instructions?

<p>Timing and Control Unit (C)</p> Signup and view all the answers

What is the main role of the Flag Register in the 8085 microprocessor?

<p>To analyze test conditions through various flags (D)</p> Signup and view all the answers

What operation does the Adder component of the ALU in the 8085 perform?

<p>Arithmetic Operations like addition and subtraction (D)</p> Signup and view all the answers

Which of the following registers in the 8085 is specifically used for addressing memory locations?

<p>Memory Address Register (C)</p> Signup and view all the answers

What is the function of the Address Bus in the 8085 microprocessor architecture?

<p>Identify memory addresses for instruction fetching (B)</p> Signup and view all the answers

Which signal indicates that the data bus is ready to send data during an operation in the 8085 microprocessor?

<p>ALE (B)</p> Signup and view all the answers

In the context of the 8085 microprocessor, what does the acronym 'PSW' stand for?

<p>Program Status Word (B)</p> Signup and view all the answers

What is the bit-length of the registers BC, DE, and HL when paired for 16-bit operations in the 8085 microprocessor?

<p>16 bits (B)</p> Signup and view all the answers

Which component within the 8085 architecture performs operations such as rotate left and shift right?

<p>Shifter (A)</p> Signup and view all the answers

Which of the following describes how the 8085 microprocessor communicates internally with I/O devices?

<p>Using the System Bus comprising Address, Data, and Control Bus (B)</p> Signup and view all the answers

How does the 8085 microprocessor handle power supply requirements?

<p>Using a fixed +5V power supply (D)</p> Signup and view all the answers

Which of the following is NOT a type of interrupt signal used by the 8085?

<p>HOLD (D)</p> Signup and view all the answers

During the reset state of the 8085 microprocessor, what is the initial value of the Program Counter (PC)?

<p>0000 (A)</p> Signup and view all the answers

What function do the HOLD and HLDA signals serve in the 8085 microprocessor?

<p>Indicate Direct Memory Access requests (C)</p> Signup and view all the answers

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Study Notes

8085 Microprocessor Architecture

  • Developed by Intel in 1977, it is an 8-bit microprocessor capable of addressing 64KB of memory.
  • Utilizes NMOS technology and operates on a single +5V power supply with a 3.2 MHz clock speed.
  • Consists of an 8-bit ALU, providing arithmetic and logical operations.
  • Its architecture includes units like ALU, Timing and Control unit, Interrupt Control, Serial I/O Control, registers, and the CPU as its core.

ALU

  • Performs arithmetic operations like addition, subtraction, increment, decrement, and logical operations like AND, OR.
  • Its word length is determined by its internal data bus, which is 8-bits in the 8085.
  • Contains components like Adder, Shifter and Status register.

Timing and Control Unit

  • Responsible for generating control signals for various operations like memory and I/O management.
  • Provides timing, control, and status signals, orchestrating communication between the CPU, memory, and peripheral devices.

System Bus

  • 8085 communicates with memory and I/O devices via the Address bus, Data bus, and Control bus.
  • Data Bus: Bi-directional, carries instructions and data between microprocessor and memory. Its size denotes the type of arithmetic operation possible.
  • Address Bus: Unidirectional, transmits instructions from the microprocessor to memory. Its size determines the memory capacity the 8085 can address.
  • Control Bus: Includes unidirectional and bi-directional signals, responsible for synchronizing and coordinating operations between the microprocessor and peripheral devices.

Registers

  • 8085 has six 8-bit general-purpose registers: B, C, D, E, H, and L. These can be paired to form 16-bit registers BC, DE, and HL for performing 16-bit operations.
  • Accumulator: An 8-bit register in the ALU, stores data and the results of arithmetic and logical operations.
  • Flag Register (Status Register): Consists of 5 flags (CF, PF, ZF, SF, AC), used to analyze the result of operations. The combined accumulator and flag register is called the Program Status Word (PSW).
  • Stack Pointer: A 16-bit register used as a memory pointer, pointing to the memory location used for stack operations.
  • Program Counter: A 16-bit register that holds the address of the next instruction to be fetched and executed.
  • Instruction Register/Decoder: Temporarily stores the current instruction from memory, decodes it, and sends the decoded data to the CPU.

8085 Microprocessor Pin Diagram

  • Utilizes combined Address/Data bus pins (A0-A15) for unidirectional signal transmission from the microprocessor to peripheral devices.
  • ALE (Address Latch Enable) signal activates the lower 8 bits of the data bus during the initial T state of the machine cycle.
  • S0 and S1 are status signals, determining the operation (read, write, halt, fetch) based on their 4 possible combinations.

8085 Addressing Modes

  • Different ways to specify operands for instructions.
  • Direct Addressing Mode: Directly specifies the memory location of the operand.
  • Register Addressing Mode: Operands are stored in registers (like B, C, D, E, H, L, Accumulator).
  • Immediate Addressing Mode: The value of the operand is directly encoded within the instruction.
  • Indirect Addressing Mode: The address of the operand is stored in a register pair (BC, DE, HL).
  • Implicit Addressing Mode: Operand is implied by the instruction itself, such as the Accumulator in some instructions.

Interrupts in 8085

  • Signals triggered by external devices, allowing the microprocessor to deviate from its normal program execution.
  • 8085 has 5 hardware interrupt signals:
    • TRAP: A non-maskable interrupt with the highest priority. Executes the ISR located at 0024H address.
    • RST 7.5: A maskable interrupt with the 2nd highest priority, executing ISR at 003CH address.
    • RST 6.5: A maskable interrupt with the 3rd highest priority, executing ISR at 0034H address.
    • RST 5.5: A maskable interrupt, executing ISR at 002CH address.
    • INTR: A maskable interrupt with the lowest priority. It is enabled during the RESET state.

8085 Applications

  • Instrumentation Domain: Used in digital kiosks, security systems, function generators, credit card systems, medical devices, and control panels (like printing presses).
  • Entertainment Industry: Implemented in gaming consoles, DVD players, and other electronic devices.
  • Communication Systems: Used in digital phones, satellite communication, telephone exchanges, and television/computer motherboards.
  • Home Appliances: Controls appliances like ovens, washing machines, and refrigerators.

Machine Cycles & Bus Timings

  • 8085 uses a series of machine cycles for instruction execution, typically consisting of four types:

    • Opcode Fetch Cycle: Retrieves the instruction code from memory based on the Program Counter.
    • Memory Read Cycle: If the instruction requires data from memory, the microprocessor fetches it.
    • Memory Write Cycle: If the instruction stores data back into memory, the microprocessor writes it.
    • I/O Read/Write Cycle: Enables data transfer between the microprocessor and I/O devices.
  • Bus timings determine the timing characteristics of data transfer over the system buses, involving:

    • Clock Speed: Typically 3 MHz in 8085, defining the rate of instruction processing.
    • Cycle Timing: Diagram showing the timing of address, data, and control signals within each machine cycle.
    • Control Signals: Manage data flow and operation of memory and I/O devices.
    • Memory and I/O Timings: Specifying time constraints for memory and I/O operations.

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