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For general knowledge for engineering grads.


(a) Memory Segmentation : Memory can be thought of as a vast collection of bytes. These bytes need to be organised in some efficient manner in order to be of any use.

(b). What are data transfer instructions and arithmetic instruction ?

  1. Data Transfer Instruction : These types of instructions are used to transfer data from source operand to destination operand. All the store, move, load, exchange, input and output instruction belong to this category. For example MOV, PUSH, XCHG etc.
  2. Arithmetic Instruction : All the instructions performing arithmetic, operation, i.e addition, subtraction, comparison, multiplication etc. For example : ADD/ADC, SUB/SBB, CMP, MUL etc.
(c). Specify the 8085 signals that are used to enable an input port.
       The 8085 signals that are used to enable an input port are as follows :
  • Power Supply Signals
  • Clock Signals
  • Reset Signals
  • Interrupt Signals
  • Status and Control signals
  • DMA request signals
  • Serial I/O signals.
(d). Explain why the number of output port in the peripheral mapped I/O is restricted to 256 port ?
            The number of output ports in peripheral I/O is restricted to 256 ports because the operand of the OUT instruction is 8 bits it can have only 256 combinations.
(e) What operation can be performed by using the instruction ADD A?
         The instruction ADD A will add the content of the accumulator to itself, this is equivalent to multiplying by 2.

(f). Define addressing mode ?
         The different methods(modes) to select (address) the operand are called the addressing modes.

(g). Explain Direct Memory Access.

        Direct Memory Access : It is a feature of modern computers that allows certain hardware subsystem within the computer system memory independently of the central processing unit (CPU).
          Without DMA, when the CPU is using programmed input/output, it is typically fully occupied for the entire duration of the read or write operation, and is thus unavailable to perform other work. With DMA, the CPU initiates the transfer, does other operation while the is in progress, and receives an interrupt from the DMA controller when the operation is done. This feature is useful any time the CPU cannot keep up with the rate of data transfer, or where the CPU needs to perform useful work while waiting for a relatively slow I/O data transfer. Many hardware systems use DMA, including disk controllers, graphics cards, network cards and sound cards. DMA is also used for intra-chip data transfer in multi-core processors. Computers that have DMA channels can transfer data to an from devices with much less CPU overhead than computers without a DMA channel. Similarly, a processing element inside a multi-core processor can transfer data to and from its local memory without occupying its processor time, allowing computation and data transfer to proceed in parallel.

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