chap6 - _____________________________________________Ch ng...

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Unformatted text preview: _____________________________________________Ch ng 6 Truy n n i ti p ng b VI - 1 CH NG 6 TRUY N N I TI P NG B GIAO TI P GI A DTE V DCE NG B CC GIAO TH C NG B Giao th c ng b nh phn Giao th c h ng bit VI IC LSI DNG TRONG TRUY N NG B USART 8251A c a Intel SSDA 6852 c a Motorola K M TRA H TH NG THNG TIN Php o t s PAR Bi u m t V ph ng di n th c hi n s ng b gi a my thu v pht trong m t h th ng thng tin hai ch truy n b t ng b v ng b c nh ng i m khc bi t : - Ch truy n b t ng b : pht b n tin ng i ta pht i t ng k t m t v s ng b c th c hi n cho t ng k t ny b i cc bit Start v Stop thm vo tr c v sau m i k t . Xung ng h c t o ra m t cch ring r my thu v my pht. Nh v y, s ng b c th c hi n chnh xc khi t n s xung ng h my thu hon ton ng v i t n s xung ng h my pht, n u khng tin t c nh n c s c l i. - Ch truy n ng b : pht m t b n tin ng i ta xem n l m t kh i v pht i m t l n c kh i , s ng b c th c hi n b ng cch cho my pht pht km theo tn hi u d li u cc xung ng h m my thu khi d ra s dng ng b tn hi u my thu. Th c t , vi c ny ch c th c hi n khi h th ng thu pht khp kn v m t v t l, hay ni cch khc my pht v thu ph i g n nhau. Khi my pht khng th g i ring tn hi u xung ng h t i my thu th my thu ph i c m ch tch bit th i gian t chnh tn hi u d li u th c hi n s ng b . my thu ng b , ngoi vi c d tn hi u ng b ra, my thu ph i bi t phn bi t c ranh gi i c a m i k t vi c ph c h i b n tin khng b l i. Ta th y vi c th c hi n giao th c b t ng b t ng i n gi n, gi thnh th p nh ng hi u qu khng cao. Gi s pht m t k t m ASCII th ph i dng t nh t 9 bit (7 bit k t , 1 bit start, 1 bit stop), th t l hao l 2/9 = 0,22=22%. Trong khi , t l ny trong ch ng b l r t th p, kho ng vi %....
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This note was uploaded on 01/18/2012 for the course INFORMATIK 2011 taught by Professor Phanthuongcang during the Winter '11 term at Cornell University (Engineering School).

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chap6 - _____________________________________________Ch ng...

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