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KALINGA INSTITUDE OF INDUSTRIAL TECHNOLOGY
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- Introduction - ( 1 - 11 )
- 8085 instructon sets - ( 12 - 28 )
- 8085 architecture - ( 29 - 43 )
- 8085 instruction and timing diagram - ( 44 - 67 )
- Software developments tools and assembler - ( 68 - 90 )
- 8085 Interrupts - ( 91 - 107 )
- Memory Interfacing - ( 108 - 113 )
- Interfacing Chips :8255 - ( 114 - 132 )
- Interfacing Chips : 8259 - ( 133 - 145 )
- Interfacing Chips :8251 - ( 146 - 150 )
- 8086 intel processor - ( 151 - 170 )
- 8051 MicroController - ( 171 - 188 )

Topic:

EC-3003 :: MICROPROCESSORS AND MICROCONTROLLERS
(Credit - 4)
Unit One: Introduction
Jabir Hussain
(jabir.hussainfet@kiit.ac.in)
School of Electronics Engineering
KIIT University
July 10, 2017

1
Review of Digital Electronics
1.1
Gate Types and Truth Tables
The basic logic gates are AND, OR, NAND, NOR, XOR, INV, and BUF. The last two
are not standard terms; they stand for “inverter” and “buffer”, respectively.
Truth Tables are an easy way to represent a combinational logic output by tabulating all possible inputs. The symbols for these gates and their corresponding Boolean
expressions and truth tables are given below.
Figure 1: Basic Logic gates
1

1.2
Boolean Algebra and K-Maps
Boolean algebra can be used to formalize the combinations of binary logic states. Using
the definition of Boolean addition, multiplication and inversion, we can define all the logic
gates algebraically.
For designing any combinational circuit, we use Boolean algebra. However, for any
arbitrary circuit the boolean expression might be lengthy and cumbersome which might
lead to inefficient implementation. Thus, the need of logic minimization. One method is
through the use of Karnaugh Maps or K-Maps.
For a boolean function of n variables, x1 , x2 , . . . xn , a product term in which each
of the n variables appears once (in either its complemented or uncomplemented form) is
called a minterm. The addition or “OR”-ing of minterms give the Sum of Products.
For a boolean function of n variables, x1 , x2 , . . . xn , a sum term in which each of the
n variables appears once (in either its complemented or uncomplemented form) is called
a maxterm. The multiplication or “AND”-ing of maxterms give the Product of Sums.
1.3
Multiplexer
A multiplexer (MUX) is a device which passes one of several data inputs to one output.
Generally there are 2n data inputs and n control lines which determine which input is
steered to the output.
Hence, a MUX can take many data bits and put them, one at a time, on a single
output data line in a particular sequence. This is an example of transforming parallel
data to serial data.
By adding gate-level circuitry to MUX inputs, any arbitrary combinational function
can be realised with a 2:1 MUX. Also, any n variable combinational function can be
implemented with a 2n : 1 MUX, 2n−1 : 1 MUX and so on.
1.4
Decoder
Decoder (DEC) is basically, a combinational type logic circuit that converts the binary
code data at its input into an equivalent decimal code at its output. Generally there are
n inputs and 2n outputs. Depending on the input, the decoder activates only one of the
2

2n outputs.
Therefore, whichever output line is “HIGH” identifies the binary code present at the
input, in other words it “de-codes” the binary input and these types of binary decoders
are commonly used as Address Decoders in microprocessor memory applications.
1.5
Priority Encoder
An encoder is a combinational logic circuit that accepts an active level on one of its inputs
(inputs represents digits, such as decimal, octal and so on) and converts it to a coded
output. An encoder has 2n input lines, only one of which is activated at a given time and
produces an n-bit output code, depending on which input is activated.
However, if more than one input are active simultaneously, the output is unpredictable.
This ambiguity is resolved if priority is established so that only one input is encoded, no
matter how many inputs are active at a given point of time.
The priority encoder includes a priority function. The operation of the priority encoder
is such that if two or more inputs are active at the same time, the input having the highest
priority will take precedence.
1.6
Latches and Flip-Flops
Latches and flip-flops are the basic elements for storing information. One latch or flipflop can store one bit of information. The main difference between latches and flip-flops
is that for latches, their outputs are constantly affected by their inputs as long as the
enable signal is asserted. In other words, when they are enabled, their content changes
immediately when their inputs change. Flip-flops, on the other hand, have their content
change only either at the rising or falling edge of the enable signal. This enable signal
is usually the controlling clock signal. After the rising or falling edge of the clock, the
flip-flop content remains constant even if the input changes.
3

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