Nvis 5586A
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Ans.
The I/O devices are generally slow devices and their timing characteristics do not
match with processor timings. Hence the I/O devices are connected to system bus through
the ports.
Q20. What is a port?
Ans.
The port is a buffered I/O, which is used to hold the data transmitted from the
microprocessor to I/O device or vice-versa.
Q22. Write a short note on INTEL 8255?
Ans.
The INTEL 8255 is a I/O port device consisting of 3 numbers of 8 –bit parallel I/O
ports. The ports can be programmed to function either as a input port or as a output port
in different operating modes. It requires 4 internal addresses and has one logic LOW chip
select pin.
Q23. What is Instruction cycle?
Ans.
The sequence of operations that a processor has to carry out while executing the
instruction is called Instruction cycle. Each instruction cycle of a processor indium
consists of a number of machine cycles.
Q24. What is fetch and execute cycle?
Ans.
The instruction cycle of an instruction can be divided into fetch and execute cycles.
The fetch cycle is executed to fetch the opcode from memory. The execute cycle is
executed to decode the instruction and to perform the work instructed by the instruction.
Q25. What is the need for timing diagram?
Ans.
The timing diagram provides information regarding the status of various signals,
when a machine cycle is executed. The knowledge of timing diagram is essential for
system designer to select matched peripheral devices like memories, latches, ports, etc.,
to form a microprocessor system.
Q26. What is an Interrupt?
Ans.
Interrupt is a signal send by an external device to the processor so as to request the
processor to perform a particular task or work.
Q27. Define opcode and operand.
Ans.
Opcode (Operation code) is the part of an instruction / directive that identifies a
specific operation.
Operand is a part of an instruction / directive that represents a value on which the
instruction acts.
Q28. What is opcode fetch cycle?
Ans.
The opcode fetch cycle is a machine cycle executed to fetch the opcode of an
instruction stored in memory. Every instruction starts with opcode fetch machine cycle.
Q30. Why status signals are provided in microprocessor?
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