Page 307 - FUNDAMENTALS OF COMPUTER

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NPP Number System, Boolean Algebra and Logic Circuits 307

3.40 Application of Gates 3.40 JoQ>m| Ho$ Cn`moJ
Logic gates are basic building blocks of bm°{OH$ JoQ> H$åß`yQ>a Ho$ n[anW H$s _yb^yV BH$mB`m±
computer circuit. All the units in the computer hmoVo h¢Ÿ& H$åß`yQ>a Ho$ gmao n[anWm| _| `o g~go N>moQ>r BH$mB©
circuit use logic gates as the smallest element.
A circuit containing logic gates is called Logic H$s Vah Cn`moJ _| AmVo h¢Ÿ& bm°{OH$ JoQ>m| go {_bH$a ~Zo
circuit. Different types of logic circuits are used n[anW H$mo bm°{OH$ n[anW H$hVo h¢Ÿ& H$åß`yQ>a _| H$B©
in computers. For example, Half Adder, Full àH$ma Ho$ bm°{OH$ n[anW Cn`moJ _| AmVo h¢Ÿ& O¡go hm\$
Adder, multiplexer, Registers, Decoder, ES>a, \w$b ES>a, _pëQ>ßboŠga, {S>_pëQ>ßboŠga, a{OñQ>a,
Counters etc. {S>H$moS>a, H$mD§$Q>a Am{XŸ&
Logic gates are also useful in other bm°{OH$ JoQ>m| H$m Cn`moJ AÝ` ñWmZm| na Cn`moJ _|
electronic circuits called digital circuits. Other AmZodmbo {S>{OQ>b n[anWm| _| hmoVm h¡Ÿ& O¡go pâbn-
circuits made with the help of logic gates are
flip-flops, parity checker, parity generator, âbm°n, no[aQ>r MoH$a, no[aQ>r OZaoQ>a, EÝH$moS>a, H§$noaoQ>a,
comparator, Demultiplexer, Encoder, Half hm\$ g~Q´>oŠQ>a, \w$b g~Q´>oŠQ>a Am{XŸ&
subtractor, full subtractor etc.
CPU is the brain of computer. It includes grnr`y H$åß`yQ>a H$m _pñVîH$ hmoVm h¡Ÿ& Bg_| E.Eb.
ALU, CU and Registers. These three units of `y. gr.nr.`y VWm a{OñQ>g© hmoVo h¡Ÿ& `o VrZm| BH$mB`m±
the CPU are built with the help of logic gates.
bm°{OH$ JoQ>m| go hr ~Zr hmoVr h¢Ÿ&
3.41 Positive and Negative Logic 3.41 YZmË_H$ VWm F$UmË_H$ cm°{OH$
As we know that in digital circuits the O¡gm {H$ h_ OmZVo h¢ H§$ß`yQ>a n[anW _| OmZH$mar
information is stored in the form of 0 and 1. 0 VWm 1 Ho$ ê$n _| g§J«{hV hmoVr h¡Ÿ& ~mBZar A§H$ 0
Binary digits 0 and 1 in the digital circuits
represent voltage levels. There are two types of VWm 1 n[anW _| EH$ {ZpíMV dm°ëQ>oO ñVa H$mo Xem©Vo
voltage level definitions: h¢Ÿ& d°mëQ>oO ñVa H$s Xmo Vah H$s n[a^mfmE± hmoVr h¢:
Positive Logic: YZmË_H$ cm°{OH$:
In positive logic, a high voltage signal Bg cm°{OH$ n[a^mfm _| CÀM dmëQ>oO ""1'' H$mo
represents "1" and a low voltage signal VWm {ZåZ dm°ëQ>oO ""0'' H$mo Xem©Vm h¡Ÿ& {S>{OQ>c
represents "0". This is most frequently used
logic definition in digital circuits. For example n[anWm| _| Bg n[a^mfm H$m AË`{YH$ Cn`moJ hmoVm h¡Ÿ&
in TTL circuits +5V represents "1" and 0V O¡go TTL n[anW _| +5 Volt "1" Xem©Vm h¡ VWm 0 Volt
represents "0". "0" Xem©Vm h¡Ÿ&
Negative Logic: F$UmË_H$ cm°{OH$:
In negative logic, a high voltage represents Bg cm°{OH$ _| CÀM dm°ëQ>oO ""0'' Xem©Vm h¡ VWm
"0" and a low voltage signal represents "1". For {ZåZ d°mëQ>oO ""1'' Xem©Vm h¡Ÿ& O¡go RS-232 C H$ZoŠQ>a
example in RS-232C connector "1" represents a _| –3Volt go –15 Volt, ""1'' Xem©Vo h¢ VWm +3Volt
voltage from (– 3V to – 15V) and "0" represents go +15Volt, ""0'' Xem©Vm h¡Ÿ&
a voltage from (+ 3V to +15V).