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Micro Controller Interview Questions - Part 4

What is IMR(Interrupt mask register) ?

IMR stores the masking bits of the interrupt lines to be masked. This register can be programmed by an operation command word (OCW).

What is priority resolver ?

It determines the priorities of the bits set in the Interrupt request register (IRR), bit corresponding to the highest priority interrupt input is set in the ISR during INTA input.

What is the use of IRR ?

The interrupt request register is used to store all the interrupt levels which are requesting the service. The eight interrupt inputs sets corresponding bits of the Interrupt Request Register upon the service request.

What is Interrupt service register(ISR) ?

The interrupt service register stores all the levels that are currently being serviced.

What is the difference between SHLD and LHLD ?

  • SHLD- Store HL register pair in memory. This instruction is used to store the contents of H and L register directly in to memory.
  • LHLD- Load HL register pair from memory. This instruction copies the contents of memory location given with in the instruction in to the L register and the contents of next memory location in to the H register.

    What is the difference between STAX and LDAX ?

  • STAX rp : Store the contents of Accumulator register (A) in memory location whose address is specified by BC or DE register pair.
  • LDAX rp : Load Accumulator register (A) with the contents of memory location whose address is specified byBC or DE register pair.

    Write an assembly language program to transfer data from memory block B1 to memory block B2 ?

    MVI C,0AH; Initialize counter
    LXI H, 2200H; Initialize source memory pointer
    LXI D, 2300H; Initialize destination memory pointer
    Loop: MOV A,M; Get byte from source memory block
    STAX D; Store byte in the destination memory block
    INX H; Increment source memory pointer
    INX D; Increment destination memory pointer
    DCR C; Decrement counter
    JNZ Loop ; If counter ? 0 repeat

    What are the types of branching instructions ?

  • Jump instructions
  • Call and Return instructions
  • Restart instructions

    Write an assembly language program to add 2 BCD numbers ?

    LXI H,2200H; Initialize pointer
    MOV A,M ; Get the first number
    INX H; Increment the pointer
    ADD M ; Add two numbers
    DAA ; Convert HEX to valid
    BCD STA 2300; store the result

    Explain the instruction LXI rp,data (16) ?

    LXI rp, data(16) : Load 16 :bit immediate data to specified register pair or stack pointer. The rp is 16 bit register pairs such as BC, DE, HL or stack pointer.

    Micro Controller Interview Questions - Part 5 >>>

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