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Ｔhｅ Ｉntroｄuｃｔion of ＡT8９C5１
Descrｉption
Ｔhe AT89C51 ｉs a low-pｏwer， higｈ—ｐeｒforｍａncｅ CＭOＳ 8-bit microｃoｍputeｒ　ｗith　4K bytes　of　Flaｓh progrａｍmaｂle　aｎｄ　eｒaｓable　ｒeａd only mｅｍoｒy （ＰＥRＯM）。 The device is ｍａnufactuｒed using Atmel’s hｉgh-dｅnsity ｎonvolatiｌe　memory　teｃhｎｏloｇy and iｓ　ｃoｍpatｉbｌe with　ｔｈe　iｎduｓtry—sｔandarｄ ＭCS-51 ｉｎsｔructioｎ set． The ｏn—cｈｉp Flasｈ　allｏｗs ｔhe ｐrｏgram　mｅmory to be ｒeｐrｏgｒammed　iｎ－sｙsｔｅm or　by ａ coｎventｉonal　nonvｏlａｔile memory progrａmmｅr． By coｍｂｉniｎg a verｓａtｉle 8-bit ＣPU with Flash ｏn ａ ｍonoｌiｔhic cｈip， thｅ Atｍel　AT89C51　is　a powerful micrｏｃｏmputeｒ ｗhｉｃｈ pｒovides a highlｙ—ｆleｘｉｂlｅ anｄ ｃost—effｅctiｖe　ｓoｌutｉon to many embeddeｄ ｃontrｏl ａpplｉｃaｔions。
Funｃｔion chaｒａcｔeｒｉsｔic
Tｈe AT8９C51 ｐrovｉdes the　ｆoｌlowiｎｇ standaｒd featuｒeｓ:　4K byｔｅs of Flash，　128　byteｓ　of　ＲAM,　３２ I/O ｌｉnｅｓ,　two １6-bit　tiｍer/ｃounters，　onｅ 5　vｅctoｒ twｏ-leveｌ ｉntｅrrupt architecture, a　fｕll　dｕｐlｅx　seriａｌ ｐｏrt, oｎe—ｃhip osｃillａｔor　and clock circuitrｙ。 In ａｄdiｔion, tｈe AT８９Ｃ5１ is　ｄesigned ｗitｈ　sｔａtiｃ logｉc　fｏr oｐerａｔion dｏwn to　zeｒｏ fｒequeｎcy and sｕpｐorｔs two sｏｆtware selectable　pｏwer sａｖinｇ moｄｅｓ。　Ｔhe Ｉdle Mｏdｅ　sｔｏｐs　the CPＵ　ｗhiｌe　alｌowiｎg tｈe ＲAＭ， tｉmer／cｏunｔerｓ， serｉａl porｔ ａnd inteｒｒｕｐｔ ｓｙstｅｍ to ｃonｔinｕe funcｔioning。 The Ｐower—dowｎ Moｄe saves the RＡM conｔenｔs　bｕt　fｒeezes the oscilｌator ｄisabliｎg　all ｏther chip　ｆuncｔions until the ｎｅxt hardwaｒｅ reset.
Ｐin Descｒiptiｏｎ
ＶＣC：Supply　vｏltaｇe。
ＧＮＤ:Ｇround。
Port　0
Ｐoｒt 0 is　aｎ ８—biｔ opｅｎ—drain bｉ-ｄｉrｅcｔionａｌ I/O poｒt. As aｎ outｐuｔ port, eaｃh pin　ｃan ｓｉnk　eighｔ TTL inｐｕts．　Wｈｅn 1s ａｒe wｒiｔten to porｔ ０ pins，　the　pins can　ｂe used as hｉgｈ—ｉmpedａnce inpｕtｓ。 Porｔ 0 maｙ ａlso bｅ ｃonfigｕｒeｄ to　be ｔhe multipleｘeｄ　ａddｒesｓ／ｄａta ｂｕｓ　dｕｒing accｅssｅs to exteｒｎal program aｎｄ ｄａta ｍｅmory。 In tｈiｓ ｍode　Ｐ0 hａs　internal Pull—up resｉstor. Port 0 alｓo reｃeivｅs the ｃode　byｔes dｕring　Flash ｐｒograｍmiｎg， aｎｄ ouｔｐuts　the coｄe byteｓ ｄurｉng Prograｍ ｖeｒｉｆｉcation。　Exｔerｎal　Pulｌ—up　resistｏrs aｒe reｑuｉred ｄuriｎg Pｒogｒaｍ verification．
Pｏrt 1
Poｒt 1 ｉｓ an ８-bｉ