76. Distinguish between the memories mapped I/O peripheral I/O?
Ans:
| Memory Mapped I/O |
Peripheral MappedI/O |
| 16-bit device address |
8-bit device address |
| Data transfer between any general-purpose register and I/O port. |
Data is transfer only between accumulator and I.O port |
| The memory map (64K) is shared between I/O device and system memory. |
The I/O map is independent of the memory map; 256 input device and 256 output device can be connected |
| More hardware is required to decode 16-bit address |
Less hardware is required to decode 8-bit address |
| Arithmetic or logic operation can be directly performed with I/O data |
Arithmetic or logical operation cannot be directly performed with I/O data
|
77. What is memory mapping?
Ans: The assignment of memory addresses to various registers in a memory chip is called as memory mapping.
78. What is I/O mapping?
Ans:The assignment of addresses to various I/O devices in the memory chip is called as I/O mapping.
79. 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.
80.What is the use of 8251 chip?
8251 chip is mainly used as the asynchronous serial interface between the processor and the external equipment.
81. What is 8279?
Ans:The 8279 is a programmable Keyboard/Display interface.
82. List the major components of the keyboard/Display interface.
a. Keyboard section
b. Scan section
c. Display section
d. CPU interface section
83. 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.
84.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.
85. 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.
86. 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.
87. 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.
88. What is meant by key bouncing?
Ans:Microprocessor must wait until the key reach to a steady state; this is known as Key bounce.
89. What is swapping?
The procedure of fetching the chosen program segments or data from the secondary storage into the physical memory is called ‘swapping’.
90. 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.
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