Processors and Controllers: 8086 Microprocessor
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Questions and Answers

What signal causes the processor to immediately terminate its present activity?

RESET

What does the INTR signal represent in the 8086 microprocessor?

  • Clock input
  • Interrupt Request (correct)
  • Data Transmission
  • Address Latch Enable

    • The NMI (Non-Maskable Interrupt) is a hardware interrupt that can be disabled.

    False

    The _ pin is used to differentiate memory access and I/O access in the 8086 microprocessor.

    <p>M/</p> Signup and view all the answers

    Match the following segment registers in the 8086 microprocessor with their descriptions:

    <p>Code Segment (CS) = Contains the base or start of the current code segment Data Segment (DS) = Points to the current data segment Stack Segment (SS) = Points to the current stack Extra Segment (ES) = Points to the extra segment in which data is stored</p> Signup and view all the answers

    What mechanism is known for overlapping instruction fetch with execution in 8086 architecture?

    <p>pipelining</p> Signup and view all the answers

    Which flag is set if the result of computation or comparison is zero in 8086 architecture?

    <p>Zero Flag</p> Signup and view all the answers

    Directions Flag is used by string manipulation instructions to process strings in __________ mode.

    <p>auto incrementing</p> Signup and view all the answers

    Overflow Flag in 8086 microprocessor architecture is set if the operation result overflows the destination register.

    <p>True</p> Signup and view all the answers

    Match the following registers with their descriptions:

    <p>Stack Pointer (SP) = Used to access data in the stack segment and automatically updated during POP or PUSH Base Pointer (BP) = Contains an offset address in the current SS, used for based addressing mode Accumulator Register (AX) = Consists of two 8-bit registers AL and AH, used for I/O operations and arithmetic calculations Counter Register (CX) = Consists of two 8-bit registers CL and CH, used as a counter and in LOOP instructions</p> Signup and view all the answers

    What type of addressing mode is used when BX or BP is used as the base value for effective address in a memory operation?

    <p>Based Addressing</p> Signup and view all the answers

    String Addressing mode is employed in string operations to operate on string data.

    <p>True</p> Signup and view all the answers

    In Indirect I/O port Addressing mode, the 16-bit port address is stored in the _ register.

    <p>DX</p> Signup and view all the answers

    Match the memory addressing mode with its description:

    <p>Relative Addressing = Effective address specified relative to the Instruction Pointer by an 8-bit signed displacement Based Index Addressing = Computed from the sum of a base register, an index register, and a displacement String Addressing = Used in string operations to operate on string data</p> Signup and view all the answers

    Which register is used to hold the offset address of top stack memory?

    <p>SP</p> Signup and view all the answers

    Which register is used to hold the index value of source operand (data) for string instructions?

    <p>SI</p> Signup and view all the answers

    What is the special function of the 16-bit Accumulator register?

    <p>Stores the 16-bit results of arithmetic and logic operations</p> Signup and view all the answers

    The instruction will specify the name of the register which holds the data to be operated by the instruction. This is an example of __________ addressing.

    <p>Register</p> Signup and view all the answers

    What is the main difference between minimum and maximum mode of operation in 8086?

    <p>Minimum mode works with a single microprocessor, while maximum mode works in a multiprocessor configuration.</p> Signup and view all the answers

    The 8086 microprocessor has a 20-bit address bus for accessing memory.

    <p>True</p> Signup and view all the answers

    What signal in 8086 is used to latch the addresses and BHE signal?

    <p>ALE (Address Latch Enable)</p> Signup and view all the answers

    What does the READY signal in 8086 indicate?

    <p>acknowledgement from the slow device or memory that they have completed the data transfer</p> Signup and view all the answers

    Study Notes

    Here are the study notes in bullet points:

    • About Embedded Domain*
    • To start learning in embedded domain, you need skills in:
      • Embedded systems (electronic systems with a microprocessor or microcontroller)
      • Assembly language programming for target devices like 8086 and 8051
    • Features of 8086*
    • 16-bit processor
    • 16-bit data bus
    • 20-bit address bus (can access up to 1MB of memory)
    • 16-bit I/O address bus (can access up to 64K I/O ports)
    • Multiplexed data bus and lower order address bus
    • Fourteen 16-bit registers
    • Requires a clock with 33% duty cycle (5MHz, 8MHz, or 10MHz)
    • Powerful instruction set with various addressing modes
    • Can perform bit, byte, word, and block operations
    • Two modes of operation: Minimum and Maximum
    • Pins and Signals*
    • Classified into five groups:
      • Address/Data bus (AD0-AD15)
      • Address/Status bus (A16-S6)
      • Control and Status signals
      • Interrupts and externally initiated signals
      • Power supply and clock frequency signals
    • Each group has its own set of signals with specific functions
    • Minimum Mode Configuration*
    • Uses 8 signals for control, status, interrupt, and externally initiated functions
    • Signals include:
      • ALE (Address Latch Enable)
      • DEN (Data Enable)
      • DT/R (Data Transmit/Receive)
      • M/IO (Memory/Input-Output)
      • RD (Read)
      • WR (Write)
      • INTA (Interrupt Acknowledge)
      • HLDA (Hold Acknowledge)
    • Maximum Mode Configuration*
    • Uses 8 signals for status, instruction queue, and multiprocessor configuration control
    • Signals include:
      • QS1, QS0 (Queue Status)
      • S2, S1, S0 (Status bits)
      • LOCK (Lock signal)
      • RQ/GT (Request/Grant)
      • INTA (Interrupt Acknowledge)
    • Timing Diagram and Architecture*
    • Execution Unit (EU) executes instructions
    • Bus Interface Unit (BIU) fetches instructions, reads/writes data to memory/I/O ports
    • EU and BIU function separately### 8086 Microprocessor Architecture
    • The 8086 is a 16-bit microprocessor with a 1-megabyte memory divided into segments of up to 64K bytes each.
    • It has a Bus Interface Unit (BIU) and an Execution Unit (EU).

    Segment Registers

    • There are four segment registers:
      • Code Segment (CS)
      • Data Segment (DS)
      • Stack Segment (SS)
      • Extra Segment (ES)
    • Each segment register is 16-bit and points to a segment of memory.

    Instruction Pointer (IP)

    • The Instruction Pointer (IP) is a 16-bit register that points to the next instruction to be executed within the currently executing code segment.
    • Its content is automatically incremented as the execution of the next instruction takes place.

    Execution Unit (EU)

    • The Execution Unit (EU) decodes and executes instructions.
    • It has a decoder, a 16-bit Arithmetic Logic Unit (ALU), and four general-purpose registers (AX, BX, CX, DX).
    • The AX, BX, CX, and DX registers can be used as 16-bit registers or as two 8-bit registers.

    Registers

    • The AX register is used for I/O operations and multiplication and division instructions.
    • The BX register is used as a base register for addressing memory.
    • The CX register is used as a counter register for shift, rotate, and loop instructions.
    • The DX register is used to hold the high 16-bit result of a 16-bit multiplication and the high 16-bit dividend in a 32-bit division.

    Stack Pointer (SP) and Base Pointer (BP)

    • The Stack Pointer (SP) and Base Pointer (BP) are used to access data in the stack segment.
    • The SP is used as an offset from the current SS during execution of instructions that involve the stack segment in the external memory.
    • The BP contains an offset address in the current SS, which is used by instructions utilizing the based addressing mode.

    Source Index (SI) and Destination Index (DI)

    • The Source Index (SI) and Destination Index (DI) registers are used in indexed addressing.
    • Instructions that process data strings use the SI and DI registers together with DS and ES respectively to distinguish between the source and destination addresses.

    Flag Register

    • The flag register is 16-bit and consists of six status flags (OF, SF, ZF, AF, PF, and CF) and three control flags (DF, IF, and TF).

    Practice Problems

    • Calculate the physical address for a given segment address and offset address.
    • Determine the status of the flag register after the execution of a sequence of instructions.### Addressing Modes in 8086 Microprocessor
    • The 8086 microprocessor has 12 addressing modes:
      • 4 modes for register and immediate data (Group I)
      • 5 modes for memory data (Group II)
      • 2 modes for I/O ports (Group III)
      • 1 mode for relative addressing (Group IV)
      • 1 mode for implied addressing (Group IV)

    Group I: Addressing Modes for Register and Immediate Data

    • Register Addressing: specifies the name of the register which holds the data to be operated
      • Example: MOV CL, DH
      • The content of 8-bit register DH is moved to another 8-bit register CL
    • Immediate Addressing: an 8-bit or 16-bit data is specified as part of the instruction
      • Example: MOV DL, 08H
      • The 8-bit data (08H) given in the instruction is moved to DL
    • Direct Addressing: not applicable in this group
    • Register Indirect Addressing: not applicable in this group
    • Based Addressing: not applicable in this group
    • Indexed Addressing: not applicable in this group
    • Based Index Addressing: not applicable in this group
    • String Addressing: not applicable in this group
    • Direct I/O port Addressing: not applicable in this group
    • Indirect I/O port Addressing: not applicable in this group
    • Relative Addressing: not applicable in this group
    • Implied Addressing: not applicable in this group

    Group II: Addressing Modes for Memory Data

    • Register Addressing: not applicable in this group
    • Immediate Addressing: not applicable in this group
    • Direct Addressing: the effective address of the memory location is given in the instruction
      • Example: MOV BX, [1354H]
      • The square brackets around the 1354H denotes the contents of the memory location
    • Register Indirect Addressing: the name of the register which holds the effective address is specified
      • Example: MOV CX, [BX]
      • The content of the memory location is moved to CX
    • Based Addressing: BX or BP is used to hold the base value for effective address and a signed 8-bit or unsigned 16-bit displacement
      • Example: MOV AX, [BX + 08H]
      • The effective address is calculated from BX and DS
    • Indexed Addressing: SI or DI register is used to hold an index value for memory data and a signed 8-bit or unsigned 16-bit displacement
      • Example: MOV CX, [SI + 0A2H]
      • The effective address is calculated from SI and DS
    • Based Index Addressing: the effective address is computed from the sum of a base register (BX or BP), an index register (SI or DI), and a displacement
      • Example: MOV DX, [BX + SI + 0AH]
      • The effective address is calculated from BX, SI, and DS
    • String Addressing: employed in string operations to operate on string data
      • Example: MOVS BYTE
      • The effective address of source data is stored in SI register and the EA of destination is stored in DI register
    • Direct I/O port Addressing: not applicable in this group
    • Indirect I/O port Addressing: not applicable in this group
    • Relative Addressing: not applicable in this group
    • Implied Addressing: not applicable in this group

    Group III: Addressing Modes for I/O Ports

    • Register Addressing: not applicable in this group
    • Immediate Addressing: not applicable in this group
    • Direct Addressing: an 8-bit port address is directly specified in the instruction
      • Example: IN AL, [09H]
      • The content of port with address 09H is moved to AL register
    • Register Indirect Addressing: the instruction specifies the name of the register which holds the port address
      • Example: OUT [DX], AX
      • The content of AX is moved to port whose address is specified by DX register
    • Based Addressing: not applicable in this group
    • Indexed Addressing: not applicable in this group
    • Based Index Addressing: not applicable in this group
    • String Addressing: not applicable in this group
    • Direct I/O port Addressing: not applicable in this group
    • Indirect I/O port Addressing: not applicable in this group
    • Relative Addressing: not applicable in this group
    • Implied Addressing: not applicable in this group

    Group IV: Relative Addressing Mode

    • The effective address of a program instruction is specified relative to Instruction Pointer (IP) by an 8-bit signed displacement
      • Example: JZ 0AH
      • If ZF = 1, then the program control jumps to new address calculated above

    Group IV: Implied Addressing Mode

    • Instructions using this mode have no operands
    • The instruction itself will specify the data to be operated by the instruction
      • Example: CLC
      • This clears the carry flag to zero

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    Learn about the 8086 microprocessor, its features, and working with assembly language programs for target devices like 8086 and 8051. Develop essential skills for embedded systems and computer languages.

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