Microprocessors And Interfacing

The DAD (Double Add) instruction in the 8085 microprocessor adds the contents of a specified register pair to the contents of the HL register pair. DAD H adds HL to itself, effectively performing HL = HL + HL.

The instruction SUB AL, BL performs the operation AL = AL − BL. In this case: AL = 3AH, BL = 49H. Performing the subtraction: 3AH − 49H = −0F H. In hexadecimal, negative results are represented in two’s complement form: −0F H = F1H. Carry Flag (CF): Since the result of the subtraction is negative, a borrow occurs, setting CF = 1. Sign Flag (SF): The most significant bit (MSB) of the result is 1, indicating a negative number, so SF = 1.

- Software interrupts are triggered by executing instructions in a program and are not related to external hardware signals. - RST 5 is a software interrupt, as it is explicitly called by the program to handle specific tasks. - Other options: INTR: A general-purpose hardware interrupt. RST 6.5: A vectored hardware interrupt. TRAP: A non-maskable hardware interrupt.

In cycle stealing mode, the DMA controller temporarily halts the CPU during alternate clock cycles to access the system bus for transferring data between I/O devices and memory. This allows the CPU and DMA controller to share the bus, minimizing performance loss.

In Direct Memory Access (DMA), after the transfer of data between peripherals and memory is completed, the processor needs to be notified so it can resume processing. This is typically done through an Interrupt signal, which halts the processor to notify it of the completion of the DMA transfer.

The correct sequence of fields in an assembly language instruction is: 1. Label field: Used for marking a location in memory. 2. Mnemonic field: Specifies the operation or instruction (e.g., ADD, SUB). 3. Operand field: Provides data or the address for the instruction to operate on. 4. Comment field: Used for adding descriptive comments for clarity.

Supervisor mode is entered when the processor encounters a software interrupt instruction. Thus, A matches with I. Abort mode is entered in response to a memory fault. Thus, B matches with II. Fast interrupt mode is entered whenever the processor receives an interrupt signal from the designated fast interrupt source. Thus, C matches with III. Interrupt mode is entered whenever the processor receives an interrupt signal from any other interrupted source. Thus, D matches with IV. Therefore, the correct answer is: (4) (A) - (I), (B) - (II), (C) - (III), (D) - (IV).