Question

Two control signals in microprocessorwhich are related to Direct Memory Access (DMA) are

Answer 1

Basic DMA Operation:

---

• Direct Memory Access (DMA) is a method of allowing data to be moved from one location to another in a computer without intervention from the central processor (CPU).
• It is also a fast way of transferring data within (and sometimes between) computer.
• The DMA I/O technique provides direct access to the memory while the microprocessor is temporarily disabled.
• The DMA controller temporarily borrows the address bus, data bus and control bus from the microprocessor and transfers the data directly from the external devices to a series of memory locations (and vice versa).
• Two control signals are used to request and acknowledge a direct memory access (DMA) transfer in the microprocessor-based system.
  1. The HOLD signal as an input(to the processor) is used to request a DMA action.
  2. The HLDA signal as an output that acknowledges the DMA action.
• When the processor recognizes the hold, it stops its execution and enters hold cycles.
• HOLD input has higher priority than INTR or NMI.
• The only microprocessor pin that has a higher priority than a HOLD is the RESET pin.
• HLDA becomes active to indicate that the processor has placed its buses at high-impedance state.

It is advised you be processor specific unlike 8086, 8085. Refer the link mentioned below for detailed reading on the same as mentioned here under:

http://www.electronics.dit.ie/staff/tscarff/DMA/dma.htm

Comments

In ques regarding the instructions it is advisable to be processor specific. Yeah, because there is a slight variation in instructions as per the version of the processor.