Short Question And Answer Microprocessor Set-13

1. How long the INTR pulse stays high?
The INTR pulse can remain high until the interrupt flip-flop is set by the EI instruction in the service routine.

2. What is the purpose of 8255 PPI?
The 8255A is widely used, programmable, parallel I/O device .It can be programmed to transfer data under various conditions, from simple I/O to interrupt I/O.

3. List the operating modes of 8255A PPI?

  • Two 8-bit ports (A and B)
  • Two 4-bit ports(Cu and CL )
  • Data bus buffer
  • Control logic

4. Specify the bit of a control word for the 8255, which differentiates between the I/O mode and the BSR mode?
BSR mode D7=0, and I/O mode D5=1

5. Write the input /output feature in Mode 9 for the 8255A PPI?

  • Outputs are latched
  • Inputs are not latched
  • Ports do not have handshake or interrupt capability

6. Write down the output control signals used in 8255A PPI?

  • OBF Output Buffer Full
  • ACK Acknowledgement
  • INTR Interrupt request
  • INTE Interrupt Enable

7. What is the use of mode 2 in 8255A PPI?
The mode is used primarily in applications such as data transfer between two computers or floppy disk controller interface.

8. List the major components of 8257 keyboard/display interface?

  • Keyboard section D7 D6 D5 D4 D3 D2D1D0 0 X X X Bit Select S/R
  • Scan section
  • Display section
  • MPU interface

9. What is the purpose for scan section in keyboard interface?
The scan section has a scan counter and four scan lines. These scan lines can be decoded using a 4-to-16 decoder to generate 16 lines for scanning.

10. What is USART?
USART is an integrated circuit. It is a programmable device its function and specifications for serial I/O can be determined by writing instructions in its internal registers.

11. Define parallel to serial conversion?
In serial transmission an 8-bit parallel word should be converted in to a stream of eight serial bits. This is known as parallel to serial conversion.

12. Define simplex transmission?
In simplex transmission, data are transmitted in only one direction. Example: transmission from a microcomputer to a printer.

13. Define Baud?
The rate at which the bits are transmitted is called Baud.

14. List the major components of 8251A programmable communication interface?

  • Read/Write control logic
  • Three buffer registers
  • Data registers
  • Control register transmission receiver
  • Data bus buffer
  • Modem control

15. Write the steps necessary to initialize a counter in write operation?

  • Write a control word into the control register
  • Load the low-order address byte
  • Load the high order byte

16. Give the various modes of 8254 timer?

  • Mode 0:interrupt or terminal count
  • Mode 1:Rate generator
  • Mode 3:square wave generator
  • Mode 4:software triggered strobe
  • Mode 5:hardware triggered strobe

17. What is read back command in 8254 timer?
The Read Back command in 8254 allows the user to read the count and the status of the counter.

18. What is transmitter section in USART?
The transmitter section accepts parallel data from the MPU and converts them into serial data. It has two registers. A buffer register and an output register

20. Define serial to parallel conversion?
In serial reception, the MPU receives a stream of eight bits and it is converted in to 8-bit parallel word. This is known as serial to parallel conversion.