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-