Page 42 - FUNDAMENTALS OF COMPUTER

42 Fundamentals of Computers NPP

switch. There is one keyswitch for each letter, H$spñdM ~ZVm h¡Ÿ& àË`oH$ Aja, A§H$ `m {MÝh hoVw EH$
number or symbol. When a key is pressed, the H$spñdM hmoVm h¡Ÿ& O~ ^r Hw§$Or H$mo X~m`m OmVm h¡, Vmo
keyswitch is activated. The circuit in a key- pñdM Ep³Q>d hmo OmVm h¡Ÿ& H$s~moS>© H$m n[anW Bg Hw§$Or
board generates a binary code for each key Ho$ gmnoj ~mBZar g§»`m àXmZ H$aVm h¡ Ÿ& H$m¡Z-gr Hw§$Or
pressed. Detecting which key is pressed and X~m`r J`r h¡ BgH$m nVm bJmZm VWm ~m`Zar H$moS>
generating binary code is called encoding. The CËnÝZ H$aZm EZH$moqS>J H$hbmVm h¡Ÿ& EZH$moqS>J gånÝZ
circuit which performs encoding is called Key- H$aZo dmbm g{H©$Q> H$s-~moS>© EZH$moS>a H$hbmVm h¡Ÿ&
board encoder. The keyboard encoder may be EÝH$moS>a EH$ gab IC go {_b gH$Vm h¡ `m EH$ g§nyU©
an IC or a microcomputer chip. The binary _mBH«$moH$åß`yQ>a {Mn hmo gH$Vm h¡ Ÿ& `h ~mBZar H$moS> `m
code generated may be ASCII, EBCDIC or Hex- Vmo ASCII `m EBCDIC `m Hex-H$moS> hmo gH$Vm h¡ Ÿ&
code. There are two types of keyboards: Xmo àH$ma Ho$ H$s~moS>© hmoVo h¢…

1. Serial keyboard. 1. gr[a`b H$s~moS>©
2. Parallel keyboard. 2. g_mZm§Va H$s~moS>©
Serial Keyboard NPP gr[a`b H$s~moS>©
It sends data, bit by bit in a serial way. The `h H$s~moS>© ~mBZar H$moS> H$mo EH$-EH$ {~Q> H$aHo$
computer converts serial bit stream into paral- H$åß`yQ>a H$mo XoVm h¡ Ÿ& H$åß`yQ>a Ho$ A§Xa H$m n[anW BZ
lel word. The whole block diagram is shown {~Q²>g H$mo g_mZm§Va eãX _| ~XbVm h¡Ÿ& BgH$m g§nyU©
below: ãbm°H$ S>m`J«m_ Bg àH$ma Xem©`m Om gH$Vm h¡ …>

Keys
Serial Serial
data to
Encoder parallel
converter

Serial Keyboard Computer
Parallel Keyboard g_mZmÝVa H$s~moS>©
The whole word of binary code is trans- ~mBZar H$moS> H$s g§nyU© {~Q²>g EH$ gmW Q´>m§g\$a
mitted simultaneously. Thus, more wires are hmoVr h¢Ÿ& AV… H$åß`yQ>a d H$s~moS>© Ho$ _Ü` A{YH$ dm`g©
needed between computer and keyboard: H$s Amdí`H$Vm hmoVr h¡Ÿ&

Keys

Encoder Code Computer
Parallel
data
Parallel Keyboard