I/O Interfacing - Question and Answer

1. What is meant by DMA data transfer?

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.

2. What are the modes of operations supported by 8255?

Simple mode
Strobed I/O mode
Bidirectional mode

3. What is the usage of IRR (Interrupt Request Register)?

IRR is the register available in programmable interrupt controller (8259). It is used to store all the interrupt levels which are requesting service. IRR is cascaded with in-service register (ISR).

4. List out three of data transmission.

Simplex
Half duplex
Full duplex

5. What does it imply if 8259’s ICW -1 bit fields LTM and SNGL bits are set to zero?

LTM = 0; Edge triggered mode.
SNGL = 0; cascading with other 8259’s.

6. What is key bouncing?

Key bounching is the mechanical vibratory action of the contact making and breaking when keys are pressed in keyboard. Key bounce can be confused as the rapid pressing of a key. Since the circuit is rapidly switching ON and OFF.

7. List the uses of USARAT.

USART provides serial communication
USART functions are integrated into standard PC interface chip.
Used in GPS navigation system
Mobile applications
Industrial and control applications

8. What is the function of gate signal in 8254 timer?

The gate signal in 8254 is used as the gate input of counters. CLK0, CLK l gate signals re given to counter 0, counter 1 and counter 2 respectively.

9. List the features of 8251.

It is an universal synchronous and asynchronous communication controller.
It supports standard asynchronous protocol with
1. 5 to 8 bit character format
2. Odd, even or no parity generation and detection.
3. Automatic break detect and handling.
It has built-in Baud rate generator
It allows full duplex transmission.
It provides error detection logic, which detects parity, overrun and framing errors.
It has 28 pins; DIP package is available.

10. 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.

11. Name the modes of DMA operation.

Slave mode operation
Master mode operation

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 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 milli seconds, 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.

14. What do you mean by Simplex and Duplex transmission?

Simplex Transmission: Data is transmitted in only one direction.
Example : Transmission of data from a computer to a printer.
Duplex Transmission: Data is transmitted in both directions.
Example : Telephone

15. 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 recognised until one of the key is released. The final key released will be recognised and entered.

N-Key Rollover mode: In this mode, each key depression is treated independently. If simultaneous depression occurs, then keys are recognised and entered according to the order the keyboard scan found them.

16. What are the functions performed by Intel 8251?

8251 is used for converting parallel data to serial data or viceversa.
The data transmission or reception can be either asynchronous or synchronous.
It is used to interface MODEM and establish serial communication through MODEM over telephone lines.

17. What is a load cell?

A load cell consits of strain gauges which are arranged in bridge form and when excited by DC input, it produces an output voltage proportional to the weight or load placed on it.

18. What are the primary features of 8259?

8259 manages 8 interrupt requests (IR₀ to IR₇)
8259 can solve eight levels of interrupt priorities in a variety of modes.
With additional 8259 devices, the priority scheme can be expanded to 64 levels.
8259 is designed to operate only with 8 bit processors. 8259 A is designed to operate only with 8 bit as well as 16 bit processors.

19. What is an USART?

USART – Universal Synchronous/Asynchronous Receiver/Transmitter

The Intel 8251 (USART) is the hardware device that converts parallel to serial data and vice-versa and overcomes such overburden of large program. Hence it is called Programmable Communication Interface.

20. Define Baud rate.

The number of bits transmitted per second is called baud rate. The standard baud rates are 75, 110, 150, 300, 600, 1100, 2400, 9600 and 19200.

21. Define interfacing.

Interfacing is the designing of logic circuits (Hardware) and writing the instructions (Software) to enable the microprocessor to communicate with I/O devices.

22. 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.

23. Specify the two types of serial communication.

Synchronous serial data transmission, Asynchronous serial data transmission.

24. 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.