Page 341 - FUNDAMENTALS OF COMPUTER

NPP

NPP Memory 341

Masted ROMs are extensively used in em- BZH$mo _mBH«$moH§$Q´>moba Ho$ gmW Eå~oS>oS> {Z`§ÌU
bedded control systems in which a permanent àUmbr _| Cn`moJ _| bm`m OmVm h¡ & Eogo AZwà`moJm| _|
program resides in the ROM. The program need gm_mÝV`m àmoJ«m_ N>moQ>m d pñWa hmoVm h¡ & Bg{bE Bgo
not be modified. Therefore, masked-ROM is masked-ROM _| aI {X`m OmVm h¡ & Eogr masked-
referred to as “Program Memory”. ROM ""àmoJ««m_ _o_moar'" H$hbmVr h¡ &
Masked ROMs are produced by making a BÝh| ~ZmZo Ho$ {bE nhbo EH$ _mñH$ V¡`ma H$a {b`m
mask for the circuit. A mask is a photographic OmVm h¡Ÿ& `h _mñH$ n[anW H$m \$moQ>moJ«m{\$H$ Q>oåßboQ> hmoVm
template of the circuit. A masked-ROM con-
tains many diodes as a link. Presence of diode h¡ & EH$ _mñŠS> ROM EH$ qbH$ Ho$ ê$n _o| H$B© S>m`moS²>g
shows a ‘1’ and absence of diode shows a ‘0’. hmoVo h¢Ÿ& S>m`moS²>g H$s CnpñW{V ‘1’ VWm AZwnpñW{V ‘0’
The diodes are manufactured using Bipolar Xem©Vr h¡Ÿ& ~m`nmoba Q´>mpÝOñQ>g© `m MOSFETs H$m
Transistors or MOSFETs. Cn`moJ H$aHo$ S>m`moS²>g ~Zm`o OmVo h¢Ÿ&
PROM (Programmable ROM) PROM (àmoJ«m_o~b ROM)
PROM chip comes blank from the factory. PROM {Mn \o$ŠQ´>r go Imbr AmVr h¡ Ÿ& Bg_| ~hþV
It contains diodes as fusible links. A program gmao S>m`moS> hmooVo h¢, {OZH$mo Amdí`H$VmZwgma â`yO {H$`m
can be written by a device called PROM pro- Om gH$Vm h¡ Ÿ& Ohm± S>m`moS> ahoJm, dhm± 1 hmoJm AÝ`Wm
grammer. This device provides heavy current 0 hmoJm Ÿ& EH$ CnH$aU `h H$m`© H$aVm h¡ {Ogo PROM
for fusing a link. But once the program is àmoJ«m_a H$hVo h¢ Ÿ& `h CÀM Ymam àXmZ H$aHo$ S>m`moS>
written it cannot be erased. It is similar to your H$mo â`yO H$a XoVm h¡ & bo{H$Z EH$ ~ma àmoJ«m_ {bIZo
note-book in which you write with a dot Pen. Ho$ níMmV² Bgo hQ>m`m Zht Om gH$Vm h¡Ÿ& `o AmnH$s H$m°nr
It comes blank from the factory. Once you Ho$ g_mZ hmoVr h¡, {OZ_| Amn noZ go {bIVo h¢Ÿ& `o \o$ŠQ´>r
write with a dot pen, it cannot be erased. go Imbr AmVr h¡Ÿ& Amn EH$ ~ma hr Bg_| Hw$N> {bI
gH$Vo h¢ Ÿ& BgHo$ ~mX {g\©$ n‹T> gH$Vo h¢Ÿ&
EPROM (Erabsable PROM) EPROM (BaoOo~c àmo_)
EPROM is made up of MOSFET cells in Bg àH$ma H$s _o_moar _| Amdoe Ho$ ê$n _| OmZH$mar
which the information is stored in the form of hmoVr h¡Ÿ& `h Amdoe MOSFET H$s gob _| hmoVm h¡Ÿ& `o
charge. EPROM also comes blank from the
factory. It can be programmed by a device called ^r \o$ŠQ´>r go Imbr AmVr h¡ bo{H$Z EH$ CnH$aU,
EPROM Programmer. This device uses much EPROM àmoJ«m_a H$s ghm`Vm go Bg_| àmoJ«m_ {bI
higher voltages than the normal operating gH$Vo h¢Ÿ& ¶h CnH$aU gm‘mݶ Am°naoqQ>J dmoëQ>oO H$s
voltages. Thus, EPROM is programmable
electrically. But if we want to erase the contents Anojm A{YH$ hm¶a dmoëQ>oO Cn¶moJ H$aVm h¡& `{X BgHo$
of EPROM, an Ultraviolet light source is put for àmoJ«m_ H$mo hQ>mZm h¡, Vmo nam~¢JZr {H$aUm| H$mo H$ar~ 20
20 minutes. An Intense UV light erases the {_ZQ> VH$ Bg na S>mbVo h¡Ÿ& Bggo gmam Amdoe brH$
charge. Thus the EPROM is ready for the next hmo OmVm h¡& A~ Bg EPROM H$s {Mn _| Z`m àmoJ«m_
program. This chip is anologous to your note-
book in which you write with a pencil. You can {bIm Om gH$Vm h¡Ÿ& `o AmnH$s H$m°nr Ho$ g_mZ hmoVo h¢
erase the contents of a page with a rubber and {Og_| Amn n|{gb go {bIVo h¢Ÿ& Bgo ~ma-~ma {_Q>mH$a
new poem can be written each time. Hw$N> Z`m {bI gH$Vo h¢&