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MICROCOMPUTER TERMINOLOGY
A microprocessor is a VLSI device which operates according to a program
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e
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A microprocessor is effectively a CPU on a chip
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The MPU
performs all the basic functions of a traditional CPU except that it is less powerful
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The microprocessor instructions are coded in binary form and reside in the computer
memory
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There are
collective names for groups of binary digits:i)

a byte is a group of 8 binary digits
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b7 is the most significant bit and b0 is the least significant bit
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There are two nibbles in a byte
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It may be one or more bytes
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To say that a word is the width of the data bus
is not necessarily true in all cases
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We shall say that a word is the maximum number of bits which the CPU
can handle in parallel in any given operation such as addition
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Each microprocessor has its own instruction set which is determined by the manufacturer
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An 8051 microcontroller is similar
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An instruction is typically one, two or three bytes but consists of two parts
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g
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code) defines the task or operation to be performed ( eg
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The operand defines the data or the address relating to the data which is to be used by the
operation
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b15
0

b14
0

b13
0

b12
1

b11
0

b10
0

1

b9
1

b8
0

b7
0

b6
0

2

b5
1

b4
1

b3
0

b2
1

3

High order byte

b1
0

b0
0

4
Low order byte

However, a typical PIC microcontroller instruction is a 14 bit word and contains the op
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b13

b0

A mnemonic is an aid to memory
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The instruction set of a microprocessor can contain hundreds of different instructions
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memory
hex
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A machine
code program is, strictly speaking, a series of binary instructions though for convenience we
generally call a hex
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The microprocessor can only respond to
machine code instructions
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