Short Question And Answer Microprocessor Set-18

1. What is an USART?
Ans:USART stands for universal synchronous/Asynchronous Receiver/Transmitter. It is a programmable communication interface that can communicate by using either synchronous or asynchronous serial data.

2.What is the use of 8251 chip?
8251 chip is mainly used as the asynchronous serial interface between the processor and the external equipment.

3. What is 8279?
Ans:The 8279 is a programmable Keyboard/Display interface.

4. List the major components of the keyboard/Display interface.
a. Keyboard section b. Scan section c. Display section d. CPU interface section

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

6.Define HRQ?
Ans: The hold request output requests the access of the system bus. In non- cascaded 8257 systems, this is connected with HOLD pin of CPU. In cascade mode, this pin of a slave is connected with a DRQ input line of the master 8257, while that of the master is connected with HOLD input of the CPU.

7. What is the use of stepper motor?
Ans:A stepper motor is a device used to obtain an accurate position control of rotating shafts. A stepper motor employs rotation of its shaft in terms of steps, rather than continuous rotation as in case of AC or DC motor.

8. What is TXD?
Ans: TXD- Transmitter Data Output This output pin carries serial stream of the transmitted data bits along with other information like start bit, stop bits and priority bit.

9. What is RXD?
Ans: RXD- Receive Data Input This input pin of 8251A receives a composite stream of the data to be received by 8251A.

10. What is meant by key bouncing?
Ans:Microprocessor must wait until the key reach to a steady state; this is known as Key bounce.

11. What is swapping?
The procedure of fetching the chosen program segments or data from the secondary storage into the physical memory is called ‘swapping’.

12. Write the function of crossbar switch?
Ans: The crossbar switch provides the inter connection paths between the memory module and the processor. Each node of the crossbar represents a bus switch. All these nodes may be controlled by one of these processors or by a separate one altogether.

13. What is a data amplifier?
Ans: Transceivers are the bi-directional buffers are some times they are called as data amplifiers. They are required to separate the valid data from the time multiplexed address data signal. They are controlled by 2 signals i.e DEN & DT/R.

14. What is status flag bit?
Ans: The flag register reflects the results of logical and arithmetic instructions. The flag register digits D0, D2, D4, D6, D7 and D11 are modified according to the result of the execution of logical and arithmetic instruction. These are called as status flag bits.

15. What is a control flag?
Ans: The bits D8 and D9 namely, trap flag (TF) and interrupt flag (IF) bits, are used for controlling machine operation and thus they are called control flags.

16. What is instruction pipelining?
Ans: Major function of the bus unit is to fetch instruction bytes from the memory. In fact, the instructions are fetched in advance and stored in a queue to enable faster execution of the instructions. This concept is known as instruction pipelining.

17. Compare Microprocessor and Microcontroller.
 Microprocessor contains ALU,general purpose registers,stack pointer, program counter, clock timing circuit and interrupt circuit.

Microcontroller contains the circuitry of microprocessor and in addition it has built- in ROM, RAM, I/O devices, timers and counters.

Microprocessor- It has many instructions to move data between memory  and CPU.

Microcontroller- It has one or two instructions to move data between memory and CPU.
It has one or two bit handling instructions. It has many bit handling instructions.
Access times for memory and I/O devices are more. Less access times for built-in memory and I/O devices.

Microprocessor based system requires more hardware.

Microcontroller based system requires less hardware reducing PCB size and increasing the reliability.