微机原理ch06MEMORYANDMEMORYINTERFACING1Word文档格式.docx

微机原理ch06MEMORYANDMEMORYINTERFACING1Word文档格式.docx

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MemorychipsareorganizedintoanumberoflocationswithintheIC.Eachlocationcanhold1bit,4bits,8bits,oreven16bits,dependingonhowitisdesignedinternally.

Thenumberofbitsthateachlocationwithinthememorychipcanholdisalwaysequaltothenumberofdatapinsonthechip.

Howmanylocationsexistsinsideamemorychipdependsonthenumberofaddresspins.ThenumberoflocationswithinamemoryICalwaysequals2xwherexisthenumberofaddresspins.

Therefore,thetotalnumberofbitsthatamemorychipcanstoreisequaltothenumberoflocationstimesthenumberofdatabitperlocation.

Tosummary:

1）Eachmemorychipcontains2xlocations,wherexisthenumberofaddresspinsonthechip.

2）Eachlocationcontainsybits,whereyisthenumberofdatapinsonthechip.

3）Theentirechipwillcontain2x×

ybits,wherexisthenumberofaddresspinsonthechipandyisthenumberofdatapinsonthechip.

4）The2x×

yisreferredtoastheorganizationofthememorychip,wherexisthenumberofaddresspinsonthechipandyisthenumberofdatapinsonthechip.

5）For2x,use表61togivethenumberoflocationsinKorMunits.

表61Powersof2

x

2x

10

1K

11

2K

12

4K

13

8K

14

16K

15

32K

16

64K

17

128K

18

256K

19

512K

20

1M

21

2M

22

4M

23

8M

24

16M

32

4G

Example1

Agivenmemorychiphas12addresspinsand8datapins.Find:

1）theorganization

2）thecapacity

Solution:

1）Thismemorychiphas4096locations（212=4096）,andeachlocationcanhold8bitsofdata.Thisorganizationof4096×

8,oftenrepresentedas4K×

8.

2）Thecapacityisequalto32Kbitssincethereisatotalof4Klocationsandeachlocationscanhold8bitsofdata.

Example2

A512Kmemorychiphas8pinsfordata.Find:

2）thenumberofaddresspinsforthismemorychip

1）Amemorychipwith8datapinsmeansthateachlocationwithinthechipcanhold8bitsofdata.Tofindthenumberoflocationswithinthismemorychip,dividethecapacitybythenumberofdatapins.512K/8=64K;

therefore,theorganizationforthismemorychipis64K×

2）Thischiphas16addresslinessince216=64K.

6.1.3Speed

Oneofthemostimportantcharacteristicsofamemorychipisthespeedatwhichdatacanbeaccessedfromit.

Toaccessthedata,theaddressispresentedtotheaddresspins,andafteracertainamountoftimehaselapsed,thedatashowupatthedatapins.

Theshorterthiselapsedtime,thebetter,andconsequently,themoreexpensivethememorychip.

Thespeedofthememorychipiscommonlyreferredtoasitsaccesstime.Theaccesstimeofmemorychipsvariesfromafewnanosecondstohundredsofnanoseconds,dependingontheICtechnologyusedinthedesignandfabrication.

6.1.4ROM（read-onlymemory）

ROMisatypeofmemorythatdoesnotloseitscontentswhenthepoweristurnedoff.Forthisreason,ROMisalsocallednonvolatilememory.

Therearedifferenttypesofread-onlymemory,suchasPROM,EPROM,EEPROM,flashROM,andmaskROM.

6.1.5PROM（programmableROM）orOTPROM

PROMisreferredtothekindofROMthattheusercanburninformationinto,PROMisauser-programmablememory.

ForeverybitofthePROM,thereexistsafuse.PROMisprogrammedbyblowingthefuses（blowafuse使保险丝熔断）.

IftheinformationburnedintoPROMiswrong,PROMmustbediscardedsinceinternalfusesareblownpermanently.Forthisreason,PROMisalsoreferredtoasOTP（one-timeprogrammable）.TheprocessofprogrammingROMisalsocalledburningROMandrequiresspecialequipmentcalledaROMburnerorROMprogrammer.

6.1.6EPROM（erasableprogrammableROM）

EPROMwasinventedtoallowchangesinthecontentsofPROMafteritisburned.InEPROM,onecanprogramthememorychipanderaseitthousandsoftimes.

AllEPROMchiphaveawindowthatisusedtoshineultraviolet（UV）（紫外线）radiationtoeraseitscontents.TheonlyproblemwithEPROMisthaterasingitscontentscantakeupto20minutes.EPROMisalsoreferredtoasUV-erasableEPROMorsimplyUV-EPROM.

ThemajordisadvantageofUV-