Short Question And Answer Microprocessor Set-5

1.How is the instruction set of 8087 classified?

  • Data transfer instructions
  • Arithmetic instructions
  • Compare instructions
  • Transcendental instructions
  • Load constant instructions
  • Processor control instructions

2.Explain the features of IOP 8089.

  • An IOP can fetch and execute its own instructions.
  • Instructions are specially designed for I/O processing.
  • In addition to data transfer, 8089 can perform arithmetic and logic operations, branches, searching and translation.
  • IOP can transfer data from an 8-bit source to 16-bit destination and vice versa.
  • IOP does all work involved in I/O transfer including device setup, Programmed I/O, and DMA operation.
  • IOP supports multiprocessing environment.
  • Communication between IOP and CPU is through memory based control blocks.

3. Name the three basic network topologies.
1. The bus
2. The star
3. Token ring

4. List the features of bus arbiter.

  • Provides multi-master system bus control and arbitration.
  • Provides simple interface with 8288 bus controller.
  • Synchronizes 8086 and 8088 processors with multi-master bus.
  • Four operating modes for flexible system configuration.

5.Define interfacing.
Interfacing is the designing of logic circuits and writing the instructions to enable the microprocessor to communicate with the I/O devices.

6.What is handshake port?
The port used for exchanging the signals between I/O devices and port or between port and processor for checking or informing various condition of the device is called handshake port.

7.Define Baud Rate.
The data rate can be expressed as bits/sec or characters/sec. The term bits/sec is called baud rate.

8.Name any two important methods available for error correction during serial communication.

  • Parity bits
  • Check sum
  • Cyclic redundancy check
  • Hamming code with 4 bit parity to encode 8 bit of data

9.Define PPI.
PPI is programmable peripheral interface. It is a programmable parallel I/O device. It can be programmed to transfer data between microprocessor and I/O devices under various conditions.

10.What are the modes of operation supported by 8255?

  • Simple I/O mode
  • Strobe I/O mode
  • Bidirectional mode

11.What is the internal operating frequency of the 8279? How can you derive it from any available clock signal?
The internal operating frequency of the 8279 is 100kHz. By dividing the available clock signal by the program clock word, it is obtained.

12.What is meant by DMA operation?

State its advantages.
DMA stands for Direct Memory Access. In order to transfer bulk amount of data between memory and I/O device without the involvement of CPU, this technique is used. The advantage of DMA is faster data transfer.

13.What are the modes of operation of DMA?

  • Slave mode operation
  • Master mode operation

14.What is meant by time multiplexed LED display?
In time multiplexed LED display, at a time only one LED displays data while other LEDs remain in off condition. But within few milliseconds, next LED is turned on while all others are in off condition. This is repeated continuously so
that all LEDs seems to display data simultaneously.

15.What do you mean by simplex and duplex transmission?
Simplex: Data is transmitted in only one direction.
Eg: Transmission of data from a computer to a printer.
Duplex: Data is transmitted in both directions.
Eg: Telephone

16.What is the difference between two key lockout and N-key rollover modes in 8279?
Two-key Lockout mode:
If two keys are depressed within the debounce cycle, it is a simultaneous depression. Neither key will be recognized until one of the key is released. The final key released will be recognized and entered.
N-Key rollover:
In this mode, each key depression is treated independently. If simultaneous depression occurs, then keys are recognized and entered in the order of the keyboard scan found them.

17.What are the requirements to be met while interfacing I/O devices to microprocessor?

  • The microprocessor identifies the I/O devices through a port address and enables the read or write operations.
  • The microprocessor selects the I/O devices through a chip select and uses the control signals read to receive data and write signal to transmit data.

18.List the functions performed by 8279.

  • Keyboard scanning
  • Key debouncing
  • Keycode generation
  • Informing the key entry to CPU
  • Storing display codes
  • Output display codes to LEDs
  • Display refreshing

19.What are the main functions for interfacing a keyboard?

  • Sense a key actuation
  • Debounce the key
  • Decode the key

20.What is key bouncing?
Mechanical switches are used as keys in most of the keyboards. When a key is pressed the contacts bounce back and forth and settle down only after a small time delay (about 20 ms). Even through a key is actuated once, it will appear to have been actuated several times. This problem is called key bouncing.