Chuong 10_Truyen Thong Noi Tiep - Smith.N Studio

8/2/2019 Chuong 10_Truyen Thong Noi Tiep - Smith.N Studio

1/17

Ch-ng 10

Truyn thng ni tip ca 8051

Cc my tnh truyn d liu theo hai cch: Song song v ni tip. Trong truynd liu song song th-ng cn 8 hoc nhiu -ng dy dn truyn d liu n mtthit b ch cch xa vi b-c. V d ca truyn d liu song song l cc my in v cc

cng, mi thit b s dng mt -ng cp vi nhiu dy dn. Mc d trong cctr-ng hp nh- vy th nhiu d liu -c truyn i trong mt khong thi gian ngnbng cch dng nhiu dy dn song song nh-ng khong cch th khng th ln -c. truyn d-dx liu i xa th phi s dng ph-ng php truyn ni tip. Trong truynthng ni tip d liu -c gi i tng bt mt so vi truyn song song th mt hocnhiu byte -c truyn i cng mt lc. Truyn thng ni tip ca 8051 l ch cach-ng ny. 8051 -c ci sn kh nng truyn thng ni tip, do vy c thtruyn nhnh d liu vi ch mt s t dy dn.10.1 Cc c s ca truyn thng ni tip.

Khi mt b vi x l truyn thng vi th gii bn ngoi th n cp d liu d-idng tng khc 8 bt (byte) mt. Trong mt s tr-ng hp chng hn nh- cc my in

th thng tin n gin -c ly t -ng bus d liu 8 bt v -c gi i ti bus dliu 8 bt ca my in. iu ny c th lm vic ch khi -ng cp bus khng qu div cc -ng cp di lm suy gim thm ch lm mo tn hiu. Ngoi ra, -ng dliu 8 bt gi th-ng t. V nhng l do ny, vic truyn thng ni tip -c dng truyn d liu gia hai h thng cch xa nhau hng trm n hng triu dm. Hnh10.1 l s truyn ni tip so vi s truyn song song.

Hnh 10.1: S truyn d liu ni tip so vi s truyn song song.Thc t l trong truyn thng ni tip l mt -ng d liu duy nht -c dng

thay cho mt -ng d liu 8 bt ca truyn thng song song lm cho n khng ch rhn rt nhiu m n cn m ra kh nng hai my tnh cch xa nhau c truynthng qua -ng thoi.

i vi truyn thng ni tip th lm -c cc byte d liu phi -cchuyn i thnh cc bt ni tip s dng thanh ghi giao dch vo song song ra ni tip. Sau n c th -c truyn quan mt -ng d liu n. iu ny cng cngha l u thu cng phi c mt thanh ghi vo ni tip ra song song nhnd liu ni tip v sau gi chng thnh tng byte mt. Tt nhin, nu d liu -ctruyn qua -ng thoi th n phi -c chuyn i t cc s 0 v 1 sang m thanh dng sng hnh sin. Vic chuyn i ny thc thi bi mt thit b c tn gi lModem l ch vit tt ca Modulator/demodulator (iu ch/gii iu ch).

Serial Transfer Parallen Transfer

Sender Receiver Sender Receiver

D7

D0

Smith Nguyen Studio.


2/17

Khi c ly truyn ngn th tn hiu s c th -c truyn nh- ni trn, mt dydn n gin v khng cn iu ch. y l cch cc bn PC v IBM truyn d liun bo mch m. Tuy nhin, truyn d liu i xa dng cc -ng truyn chng hnnh- -ng thoi th vic truyn thng d liu ni tip yu cu mt modem iu ch(chuyn cc s 0 v 1 v tn hiu m thanh) v sau gii iu ch (chuyn tn hium thanh v cc s 0 v 1).

Truyn thng d liu ni tip s dng hai ph-ng php ng b v d b.

Ph-ng php ng b truyn mt khi d liu (cc k t) ti cng thi im trong khi truyn d b ch truyn tng byte mt. C th vit phn mm s dng mt tronghai ph-ng php ny, nhng ch-ng trnh c th rt di v bun t. V l do ny mnhiu nh sn xut cho ra th tr-ng nhiu loi IC chuyn dng phc v cho truynthng d liu ni tip. Nhng IC ny phc v nh- cc b thu pht d b tng hpVART (Universal Asynchronous Receiver Transmitter) v cc b thu pht ng db tng hp UBART (Universal Asynchronous Receiver Transmitter). B vi iukhin 8051 c mt ci sn mt UART m n s -c bn k mc 10.3.

Hnh 10.2: Truyn d liu n cng, bn cng v song cng.10.1.1 Truyn d liu bn cng v song cng.

Trong truyn d liu nu d liu c th -c va pht v va -c thu th gil truyn song cng. iu ny t-ng phn vi truyn n cng chng hn nh- ccmy in ch nhn d liu t my tnh. Truyn song cng c th c hai loi l bn songcng v song cng hon ton ph thuc vo truyn d liu c th xy ra ng thikhng? Nu d liu -c truyn theo mt -ng ti mt thi im th -c gi ltruyn bn song cng. Nu d liu c th i theo c hai -ng cng mt lc th gi lsong cng ton phn. Tt nhin, truyn song cng i hi hai -ng d liu (ngoi-ng m ca tn hiu), mt pht v mt thu d liu cng mt lc.10.1.2 Truyn thng ni tip d b v ng khung d liu.

D liu i vo u thu ca -ng d liu trong truyn d liu ni tip ton lcc s 0 v 1, n tht l kh lm cho d liu y c ngha l nu bn pht v bn thukhng cng thng nht v mt tp cc lut, mt th tc, v cch d liu -c nggi, bao nhiu bt to nn mt k t v khi no d liu bt u v kt thc.10.1.3 Cc bt bt u v dng.

Truyn thng d liu ni tip d b -c s dng rng ri cho cc php truynh-ng k t, cn cc b truyn d liu theo khi th s dng ph-ng pht ng b.Trong ph-ng php d b, mi k t -c b tr gia cc bt bt u (start) v bt dng

B pht B thu

B pht

B thu

B thu

B pht

B pht

B thu

B thu

B pht

Bn n cng

Song cng

n cng



3/17

(stop). Cng vic ny gi l ng gi d liu. Trong ng gi d liu i vi truynthng d b th d liu chng hn l cc k t m ASCII -c ng gi gia mt btbt u v mt bt dng. Bt bt u lun lun ch l mt bt, cn bt dng c th lmt hoc hai bt. Bt bt u lun l bt thp (0) v cc bt dng lun l cc bt cao (bt1). V d, hy xt v d trn hnh 10.3 trong k tA ca m ASCII (8 bt nhphn l 0100 0001) ng gi khung gia mt bt bt u v mt bt dng. L-u rngbt thp nht LSB -c gi ra u tin.

Hnh 10.3: ng khung mt k tA ca m ASCII (41H) c tn hiu l 1

(cao) -c coi nh- l mt du (mark), cn khng c tn hiu tc l 0 (thp) th -ccoi l khong trng (space). L-u rng php truyn bt u vi start sau bt D0,bt thp nht LSB, sau cc bt cn li cho n bt D7, bt cao nht MSB v cui cng lbt dng stop bo kt thc k tA.

Trong truyn thng ni tip d b th cc chp IC ngoi vi v cc modem c th-c lp trnh cho d liu vi kch th-c theo 7 bt hoc 8 bt. y l ch-a k cc btdng stop c th l 1 hoc 2 bt. Trong khi cc h ASCII c hn (tr-c y) th cc kt l 7 bt th ngay nay do vic m rng cc k tASCII nn d liu nhn chung l 8bt. Trong cc h c hn do tc chm ca cc thit b thu th phi s dng hai btdng m bo thi gian t chc truyn byte k tip. Tuy nhin, trong cc my tnhPC hin ti ch s dng 1 bt stop nh- l chun.

Gi s rng chng ta ang truyn mt tp vn bn cc k tASCII s dng 1bt stop th ta c tng cng l 10 bt cho mi k t gm: 8 bt cho k tASCII chunv 1 bt start cng 1 bt stop. Do vy, i vi mi k t 8 bt th cn thm 2 b v chi lmt 25% tng ph.

Trong mt s h thng nhm duy tr tnh ton vn ca d liu th ng-i tacn thm mt bt l (parity bt). iu ny c ngha l i vi mi k t (7 hoc 8 bttu tng h) ta c thm mt bt ngoi cc bt start v stop. Bt chn l l bt chn hocbt l. Nu l bt l l s bt ca d liu bao gm c bt chn l s l mt s l cc s 1.T-ng t nh- vy i vi tr-ng hp bt chn th s bt ca d liu bao gm c btchn l s l mt s chn ca cc s 1. V d, k tA ca m ASCII dng nhphn l 0100 0001, c bt 0 l bt chn. Cc chp UART u cho php vic lp trnhbt chn l v chn, l hoc khng phn bit chn l.10.1.4 Tc truyn d liu.

Tc truyn d liu trong truyn thng d liu ni tip -c gi l bt tronggiy bps (bt per second). Ngoi ra, cn -c s dng mt thut ng rng ri na ltc baud. Tuy nhin, cc tc baud v bps l hon ton khng bng nhau. iu nyl do tc baud l thut ng ca modem v -c nh ngha nh- l s ln thay i catn hiu trong mt giy. Trong cc modem c nhng tr-ng hp khi mt s thay ica tn hiu th n truyn vi bt d liu. Nh-ng i vi mt dy dn th tc baudv bps l nh- nhau nn trong cun sch ny chng ta c th dng thay i cc thutng ny cho nhau.

0 0 0 0 0 0

d7

1 1 StartbtSpace

Stopbt Mark

d0Goes out last Goes out first



4/17

Tc truyn d liu ca mt h my tnh cho ph thuc vo cc cngtruyn thng kt ni vo trong h thng o. V d, cc my tnh PC/XT tr-c y caIBM c th truyn d liu vi tc 100 n 9600 bps. Tuy nhin, trong nhng nmgn y th cc my tnh PC da trn Pentium truyn d liu vi tc ln ti56kbps. Cn phi ni thm rng trong truyn thng d liu ni tip d b th tc baud nhn chung l b gii hn 100.000 bps.10.1.5 Cc chun RS232.

cho php t-ng thch gia cc thit b truyn thng d liu -c sn xutbi cc hng khc nhau th mt chun giao din -c gi l RS232 -c thit lpbi hip hi cng nghip in tEIA vo nm 19960. Nm 1963 n -c sa chnhv -c gi l RS232A v vo cc nm 1965 v 1969 th -c i thnh RS232B vRS232C. y chng ta n gin ch ni n RS232. Ngy nay RS232 l chun giaodin I/O vo ra ni tip -c s dng rng ri nht. Chun ny -c s dng trongmy tnh PC v hng lot cc thit b khc nhau. Tuy nhin, v n -c thit lp tr-ch lgc TTL rt lu do vy in p u vo v u ra ca n khng t-ng thch vimc TTL. Trong RS232 th mc 1 -c biu din bi 3v n 25v trong khi mc 0th ng vi in p +3v n +25v lm cho in p 3v n +3v l khng xc nh.V l do ny kt ni mt RS232 bt k n mt h vi iu khin th ta phi s dng

cc b bin i in p nh- MAX232 chuyn i cc mc lgc TTL v mc inp RS232 v ng-c li. Cc chp IC MAX232 nhn chung -c coi nh- c b iukhin -ng truyn. Kt ni RS232 n MAX232 -c tho thun phn 10.2.10.1.6 Cc chn ca RS232.

Bng 10.1 cung cp s chn ca cp RSE232 v cc tn gi ca chngth-ng -c gi l u ni DB 25. Trong l hiu th u ni cm vo (u c) gil DB 25p v u ni ci -c gi l DB 25s.

Hnh 10.4: u ni DB 25 ca RS232.V khng phi tt c mi chn u -c s dng trong cp cu my tnh PC,

nn IBM -a ra phin bn ca chun vo/ra ni tip ch s dng c 9 chn gi l DB 9 nh- trnh by bng 10:2 v hnh 10.5.

Bng 10.1: Cc chn ca RS232, 25 chn (DB 25).

S chn M t12345678

9/10

t cch ly (Protective Cround)D liu -c truyn TxD (TrNsmitted data)D liu -c phn RxD (Received data)Yu cu gi RTS (Request To Send)Xo gi CIS (Clear To Send)D liu sn sng DSR (Data Set Ready)t ca tn hiu GND (Signal Cround)Tch tn hiu mng d liu DCD (Data Carrier Detect)Nhn kim tra d liu (Received for data testing)

14 25

131



5/17

1112131415161718

19202122232425

Ch-a dngTch tn hiu mng d liu th cp (Secondary data carrier detect)Xo nhn d liu th cp (Secondary Clear to Send)D liu -c truyn th cp (Secondary Transmit Signal Element Timing)Truyn phn chia thi gian phn t tn hiu (Transmit Signal ElementTiming)D liu -c nhn th cp (Secondary Received data)Nhn phn chia thi gian phn t tn hiu (Receiveo Signal Element

Timing)Ch-a dngYu cu nhn th cp (Secondary Request to Send)u d liu sn sng (Data Terminal Ready)Pht hin cht l-ng tn hiu (Signal Qualyty Detector)Bo chung (Ring Indicator)Chn tc tn hiu d liu (Data Signal Rate Select)Truyn phn chia thi gian tn hiu (Transmit Signal Element Timing)Ch-a dng

10.1.7 Phn loi truyn thng d liu.Thut ng hin nay phn chia thit b truyn thng d liu thnh mt thit b

u cui d liu DTE (Data Terminal Equipment) hoc thit b truyn thng d liuDCE (Data Communication Equipment). DTE ch yu l cc my tnh v cc thit bu cui gi v nhn d liu, cn DCE l thit b truyn thng chng hn nh- ccmodem chu trch nhim v truyn d liu. L-u rng tt c mi nh ngha v chcnng cc chn RS232 trong cc bng 10.1 v 10.2 u xut pht t gc ca DTE.

Kt ni n gin nht gia mt PC v b vi iu khin yu cu ti thiu lnhng chn sau: TxD, RxD v t nhch ra hnh 10.6. rng trn hnh ny thcc chn TxD v RxD -c i cho nhau.

Hnh 10.5: S u ni DB 9 ca RS232.

Bng 10.2: Cc tn hiu ca cc chn u ni DB 9 trn my tnh IBM PC.

M t S chn123456789

Da ta carrier detect (DCD)Received data (RxD)Transmitted data (TxD)Data terminal ready (DTR)Signal ground (GND)Data set ready (DSR)Request to send (RTS)Clear to send (CTS)Ring indicator (RL)

Trnh tn hiu mng d liuD liu -c nhnD liu -c giu d liu sn sngt ca tn hiuD liu sn sngYu cu giXo giBo chung

6 9

51



6/17

Hnh 10.6: Ni kt khng modem.10.1.8 Kim tra cc tn hiu bt tay ca RS232.

bo m truyn d liu nhanh v tin cy gia hai thit b th vic truyn dliu phi -c phi hp tt. Chng hn nh- trong tr-ng hp ca my in, do mt thct l trong truyn thng d liu ni tip thit b thu c th khng c ch cha dliu, do phi c cch bo cho bn pht dng gi d liu. Rt nhiu chn caRS232 -c dng cho cc tn hiu bt tay. D-i y l m t v chng nh- l mt

tham kho v chng c th -c b qua v chng khng -c h tr bi chp UARTca 8051.

1. u d liu sn sng DTR: Khi thit b u cui (hoc mt cng COM ca PC)-c bt th sau khi t kim tra n gi mt tn hiu DTR bo rng n sn sngcho truyn thng. Nu c mt ci g trc trc vi cng COM th tn hiu nykhng -c kch hot. y l tn hiu tch cc mc thp v c th -c dng bo cho modem bit rng my tnh ang hot ng v ang sn sng. yl chn u ra tDTC (cng COM ca PC) v chn u ra ca modem.

2. D liu sn sng QSR: Khi DCE (chng hn modem) -c bt ln v chyxong ch-ng trnh t kim tra th n i hi DSR bo rng c sn sngcho truyn thng. Do vy, n l u ra ca modem (DCE) v u vo ca PC

(DTE). y l tn hiu tch cc mc thp. Nu v l do no m modemkhng kch hot bo cho PC bit (hoc thit b u cui) rng n khng thnhn hoc gi d liu.

3. Yu cu gi RTS: Khi thit b DTE (chng hn mt PC) c mt byte d liucn gi th n yu cu RTS bo cho modem bit rng n c mt byte cnphi gi i. RTS l mt u ra tch cc mc thp tDTE v mt u vo timodem.

4. Tn hiu xo gi CTS: p li RTS th khi modem c cha d liu mn cn nhn th n gi mt tn hiu CTS ti DTE (PC) bo rng by gi nc th nhn d liu. Tn hiu u vo ny ti DTE dng khi ng victruyn d liu.

5. Tch tn hiu mang d liu DCD: Modem yu cu tn hiu DCD bo cho DTEbit rng tch -c mt tn hiu mang d liu hp l v rng kt ni gia nv modem khc -c thit lp. Do vy, DCD l mt u ra ca modem vu vo ca PC (DTE).

6. Bo chung RI: Mt u ra t modem (DCE) v mt u vo ti my tnh PC(DTE) bo rng in thoi ang bo chung. N tt v bt ng b vi mthanh ang chung. Trong 6 tn hiu bt tay th tn hiu ny l t -c dngnht do mt thc t l cc modem chu trch nhim v tr li in thoi.Tuy nhin, nu trong mt h thng cho m PC phi chu trch nhim tr liin thoi th tn hiu ny c th -c dng.

TxD

RxD

TxD

RxD

DTE DTE

ground



7/17

T m t trn th vic truyn thng PC v modem c th -c tm tt nh- sau:Trong khi cc tn hiu DTR v DSR -c dng bi PC v modem bo rng chngang hot ng tt th cc tn hiu RTS v CTS thc t ang kim tra lung d liu.Khi PC mun gi d liu th n yu cu RTS v p li, nu modem sn sng (c chcha d liu) nhn d liu th n gi li tn hiu CTS. Cn nu khng c ch chod liu th modem khng kch hot CTS v PC thi khng yu cu DTR v th li.Cc tn hiu RTS v CTS cng -c ci nh- tn hiu lung iu khin phn cng.

n y kt thc s m tt 9 chn quan trng nht ca cc tn hiu bt tayRS232 v cc tn hiu TxD, RxD v t (Ground). Tn hiu Ground ny cng -c coinh- l tn hiu SG t ca tn hiu.10.1.9 Cc cng COM ca IBM PC v t-ng thch.

Cc my tnh IBM PC v t-ng thch da trn cc b vi x l 86 (8086, 286,384, 486 v Pentium) th-ng c hai cng COM. C hai cng COM u c cc u nikiu RS232. Nhiu my tnh PC s dng mi u ni mt kiu cm DB 25 v DB 9. Trong nhng nm gn y, cng COM1 -c dng cho chut v COM2 -c dngcho cc thit b chng hn nh- Modem. Chng ta c th ni cng ni tip ca 8051n cng COM2 ca mt my tnh PC cho cc th nghim v truyn thng ni tip.

Vi nn kin thc v truyn thng ni tip ny chng ta sn sng lm vic

vi 8051.10.2 Ni ghp 8051 ti RS232.

Nh- ni phn 10.1, chun RS232 khng t-ng thch vi mc lgc TTL,do vy n yu cu mt b iu khin -ng truyn chng hn nh- chp MAX232 chuyn i cc mc in p RS232 v cc mc TTL v ng-c li. Ni dung chnh caphn ny l bn v ni ghp 8051 vi cc u ni RS232 thng qua chp MAX232.10.2.1 Cc chn RxD v TxD trong 8051.

8051 c hai chn -c dng chuyn cho truyn v nhn d liu ni tip. Haichn ny -c gi l TxD v RxD v l mt phn ca cng P3 ( l P3.0 v P3.1).chn 11 ca 8051 l P3.1 -c gn cho TxD v chn 10 (P3.0) -c dng cho RxD.Cc chn ny t-ng thch vi mc lgch TTL. Do vy chng i hi mt b iu

khin -ng truyn chng t-ng thch vi RS232. Mt b iu khin nh- vy lchp MAX232.10.2.2 B iu khin -ng truyn MAX232.

V RS232 khng t-ng thch vi cc b vi x l v vi iu khin hin nay nnta cn mt b iu khin -ng truyn (b chuyn i in p) chuyn i cc tnhiu RS232 v cc mc in p TTL s -c chp nhn bi cc chn TxD v RxD ca8051. Mt v d ca mt b chuyn i nh- vy l chp MAX232 t hng Maxim ach Website ca hng www.maximic.com. B MAX232 chuyn i t cc mc inp RS232 s v mc in p TTL v ng-c li. Mt im mnh ca chp MAX232 ln dng in p ngung +5v cng vi in p ngun ca 8051. Hay nic cch khcvi ngun in p nui +5 chng ta m c th nui 8051 v MAX232 m khng phi

dng hai ngun nui khc nhau nh- ph bin trong cc h thng tr-c y.B iu khin MAX232 c hai b iu khin th-ng nhn v truyn d liunh- trnh by trn hnh 10.7. Cc b iu khin -ng -c dng cho TxD -c gil T1 v T2. Trong nhiu ng dng th ch c mt cp -c dng. V d T1 v R1-c dng vi nhau i vi TxD v RxD ca 8051, cn cp R2 v T2 th ch-a dngn. rng trong MAX232 b iu khin T1 c gn T1in

v T1out trn cc chn s11 v 1 t-ng ng. Chn T1in l pha TTL v -c ni ti chn RxD ca b vi iukhin, cn T1out l pha RS232 -c ni ti chn RxD ca u ni DB ca RS232.B iu khin -ng R1 cng c gn R1in v R1out trn cc chn s 13 v 12 t-ngng. Chn R1in (chn s 13) l pha RS232 -c ni ti chn TxD ca u ni DB



8/17

ca RS232 v chn R1out (chn s 12) l pha TTL m n -c ni ti chn RxD cab vi iu khin, xem hnh 10.7. rng ni ghp modem khng l ni ghp mchn TxD bn pht -c ni vi RxD ca bn thu v ng-c li.

Hnh 10.7: a) S bn trong ca MAX232b) S ni ghp ca MAX232 vi 8051 theo moden khng.

B MAX232 i hi 4 t in gi tr t 1 n 22mF. gi tr ph bin nht chocc t ny l 22mF.10.2.3 B iu khin MAX232.

tit kim khng gian trn bng mch, nhiu nh thit k s dng chpMAX232 t hng Maxim. B iu khin MAX232 thc hin cng nhng cng vicnh- MAX232 li khng cn n cc t in. Tuy nhin, chp MAX232 li t hn rtnhiu so vi MAX233 khng c s chn ging nhau (khng t-ng thch). Chng takhng th ly mt chp MAX232 ra khi mt bng mch v thay vo RS233. Hy

xem hnh 10.8 thy MAX233 khng cn n t.

Hnh 10.8: a) S bn trong ca MAX233.b) S ni ghp ca MAX233 vi 8051 theo modem khng.

10.3 Lp trnh truyn thng ni tip cho 8051.

P3.1

TxD

P3.0

RxD

Max232

8051

Vcc1314141217

11151610

18

1920

11

10 3

2 5

4 2

2 5

2

3

1

5

4

T1OUT T1IINT1IIN

R1IINR1OUT

T2IIN

R2OUT

T2OUT

R2IIN

Rs232 sideTTL side6 9

7

DB 9

P3.1

TxD

P3.0

RxD

Max232

8051

Vcc

26

7

89

11

10

5

411

10

14

13

T1OUTT1IIN

R1IINR1OUT

T2IIN

R2OUT

T2OUT

R2IIN

Rs232 sideTTL side15

16

DB 9

12

C3+

C4+

2

2 52

3

+C1

+C2



9/17

Trong phn ny chng ta s nghin cu v cc thanh ghi truyn thng ni tipca 8051 v cch lp trnh chng truyn v nhn d liu ni tip. V cc my tnhIBM PC v t-ng thch -c s dng rt rng ri truyn thng vi cc h da trn8051, do vy ta ch yu tp trung vo truyn thng ni tip ca 8051 vi cng COMca PC. cho php truyn d liu gia my tn PC v h thng 8051 m khng cbt k li no th chng ta phi bit chc rng tc baud ca h 8051 phi ph hpvi tc baud ca cng COM my tnh PC -c cho trong bng 10.3. Chng ta c

th kim tra cc tc baud ny bng cch vo ch-ng trnh Windows Terminal vbm chut ln tu chn Communication Settings. Ch-ng trnh Terminal.exe caWindow3.1 cng lm vic tt trn Windows95 v Window98. Trong Window95 vcao hn ta c th s dng chc nng Hyperterrminal. Hm Hyperterminal h tr cctc Baud cao hn nhiu so vi cc tc cho trong bng 10.3.

Bng 10.3: Cc tc Baud ca my tnh PC486 v Pentium cho trong BIOS.

V d 10.1:Vi tn sXTAL l 11.0592MHz. Hy tm gi tr TH1 cn thit c tc

baud sau:a) 9600 b) 2400 c) 1200

Li gii:Vi tn sXTAL l 11.0592MHz th ta c tn s chu trnh my ca 8051 l

11.0592MHz : 12=921.6kHz v sau ly 921.6kHz/32=28.800Hz l tn s -ccp bi UART ti b nh thi Timer1 thit lp tc .

a) 28.800/3=9600 trong 3=FD -c np vo TH1b) 28.800/12=2400 trong 12=F4 -c np vo TH1c) 28.800/24= 1200 trong 24=F8 -c np vo TH1L-u rng vic chia 1/12 ca tn s thch anh cho 32 l gi tr mc nh khi

kch hot chn RESET ca 8051. Chng ta c th thay i gi tr ci t mc nh

ny. iu ny s -c gii thch cui ch-ng.

10.3.1 Tc baud trong 8051.8051 truyn v nhn d liu ni tip theo nhiu tc khc nhau. Tc

truyn ca n c th lp trnh -c. iu y thc hin nh s tr gip ca b nhthi Timer1. Tr-c khi ta i vo bn cch lm iu nh- th no th ta s

xt quan

h gia tn s thch anh v tc baud trong 8051.Nh- ta ni ch-ng tr-c y th 8051 chia so thch anh cho 12 ly tn

s chu trnh my. Trong tr-ng hp XTAL= 11.0592MHz th tn s chu trnh l921.6kHz (11.0592MHz : 12=921.6kHz). Mch in UART truyn thng ni tipca 8051 li chia tn s chu trnh my cho 32 mt ln na tr-c khi n -c dng bib nh thi gian Timer1 to ra tc baud. Do vy, 921.6kHz : 32=28.800Hz.y l s ta s dng trong c phn ny tm gi tr ca Timer1 t tc baud.Mun Timer1 t tc baud th n phi -c lp trnh v ch lm vic mode 2, l ch thanh ghi 8 bt t ng np li. c tc baud t-ng thch vi PC ta phi

100 150 300 600 1200 2400 4800 9600 19200

XTALoscillator

12 32by UART

28800Hz

921.6kHz



10/17

np TH1 theo cc gi tr cho trong bng 10.3. V d 10.1 trnh by cch kim tra gitr d liu cho trong bng 10.3.

Bng 10.3: Cc gi tr ca thanh ghi TH1 trong Timer1 cho cc tc baudkhc nhau.

Tc baud TH1 (thp phn) TH1 (s Hex)9600

480024001200

- 3

- 6- 12- 24

FD

FAF4F8

10.3.2 Thanh ghi SBUF.SBUF l thanh ghi 8 bt -c dng ring cho truyn thng ni tip trong 8051.

i vi mt byte d liu cn phi -c truyn qua -ng TxD th n phi -c ttrong thanh ghi SBUF. T-ng t nh- vy SBUF gi mt byte d liu khi n -c nhnb -ng RxD ca 8051. SBUF c th -c truy cp bi mi thanh ghi bt k trong8051. Xt mt v d d-i y thy SBUF -c truy cp nh- th no?

MOV SBUF, # D ; Np vo SBUF gi tr 44H m ACSII ca k tD.MOV SBUF, A ; Sao thanh ghi A vo SBUF.MOV A, SBUF ; Sao SBUF vo thanh ghi A.

Khi mt byte -c ghi vo thanh ghi SBUF n -c ng khung vi cc btStart v Stop v -ng truyn ni tip quan chn TxD. T-ng t nh- vy, khi cc bt-c nhn ni tip tRxD th 8051 m khung n loi tr cc bt Start v Stop ly ra mt byte t d liu nhn -c v t n vo thanh ghi SBUF.10.3.3 Thanh ghi iu khin ni tip SCON.

Thanh ghi SCON l thanh ghi 8 bt -c dng lp trnh vic ng khung btbt u Start, bt dng Stop v cc bt d liu cng vi vic khc.

D-i y l m t cc bt khc nhau ca SCON:

Hnh 10.2: Thanh ghi iu khin cng ni tip SCON.10.3.3.1 Cc bt SM0, SM1.

y l cc bt D7 v D6 ca thanh ghi SCON. Chng -c dng xc nhch ng khung d liu bng cch xc nh s bt ca mt k t v cc bt Start vStop. Cc t hp ca chng l:

SM0 SCON.7 S xc nh ch lm vic cng ni tipSM1 SCON.6 S xc nh ch lm vic cng ni tip SM2 SCON.5 Dng cho truyn thng gia cc b vi x l (SM2= 0)REN SCON.4 Bt/xo bng phn mm cho php/khng cho thuTB8 SCON.3 Khng s dng rng riRB8 SCON.2 Khng s dng rng riT1 SCON.1 C ngt truyn t bng phn cng khi bt u bt Stop ch

1.R1 SCON.0 C ngt thu Xo bng phn mm.

SM0 SM1 SM2 REN TB8 RB8 T1 R1



11/17

SM0 SM10 0 Ch ni tip 00 1 Ch ni tip 1, 8 bt d liu, Start, Stop1 0 Ch ni tip 21 1 Ch ni tip 3

Trong bn ch ta ch quan tm n ch 1, cc ch khc -c gii

thch Appendisk A3. Trong thanh ghi SCON khi ch 1 -c chn th d liu-c ng khung gm 8 bt d liu, 1 bt Start, 1 bt Stop t-ng thch vi cngCOM ca IBM PC v cc PC t-ng thch khc. Quan trng hn l ch ni tip 1cho php tc baud thay i v -c thit lp bi Timer1 ca 8051. Trong ch ni tip 1 th mi k t gm c 10 bt -c truyn trong c bt u l bt Start, sau l 8 bt d liu v cui cng l bt Stop.10.3.3.2 Bt SM2.

Bt SM2 l bt D5 ca thanh ghi SCON. Bt ny cho php kh nng a x l ca8051 v n nm ngoi phm vi trnh by ca ch-ng ny. i vi cc ng dng cachng ta t SM2= 0 v ta khng s dng 8051 trong mi tr-ng a x l.10.3.3.3 Bt REN.

y l bt cho php thu (Receive Enable), bt D4 ca thanh ghi SCON. BtREN cng -c tham chiu nh- l SCON.4 v SCON l thanh ghi c th nh a chtheo bt. Khi bt REN cao th n cho php 8051 thu d liu trn chn RxD ca n. Vkt qu l nu ta mun 8051 va truyn v nhn d liu th bt REN phi -c t ln1. Khi t REN th b thu b cm. Vic t REN = 1 hay REN = 0 c th t -cbng lnh SETB SCON.4 v CLR SCON.4 t-ng ng. L-u rng cc lnh ny sdng c im nh a ch theo bt ca thanh ghi SCON. Bt ny c th -c dng khng ch mi vic nhn d liu ni tip v n l bt cc k quan trng trong thanhghi SCON.10.3.3.4 Bt TB8 v RB8.

Bt TB8 l bt SCON.3 hay l bt D3 ca thanh ghi SCON. N -c dng

cho ch ni tip 2 v 3. Ta t TB8 v n khng -c s dng trong cc ng dngca mnh.Bt RB8 (bt thu 8) l bt D2 ca thanh ghi SCON. Trong ch ni tip 1 th

bt ny nhn mt bn sao ca bt Stop khi mt d liu 8 bt -c nhn. Bt ny cngnh- bt TB8 rt him khi -c s dng. Trong cc ng dng ca mnh ta t RB8 = 0v n -c s dng cho ch ni tip 2 v 3.10.3.3.5 Cc bt TI v RI.

Cc bt ngt truyn TI v ngt thu RI l cc bt D1 v D0 ca thanh ghi SCON.Cc bt ny l cc k quan trng ca thanh ghi SCON. Khi 8051 kt thc truyn mtk t 8 bt th n bt TI bo rng n sn sng truyn mt byte khc. Bt TI -c btln tr-c bt Stop. Cn khi 8051 nhn -c d liu ni tip qua chn RxD v n tchcc bt Start v Stop ly ra 8 bt d liu t vo S

BUF, sau khi hon tt n bt c

RI bo rng n nhn xong mt byte v cn phi ly i ko n b mt cRI -cbt khi ang tch bt Stop. Trong cc v d d-i y s ni v vai tr ca cc bt TI vRI.10.3.4 Lp trnh 8051 truyn d liu ni tip.

Khi lp trnh 8051 truyn cc byte k t ni tip th cn phi thc hin ccb-c sau y:

1. Np thanh ghi TMOD gi tr 204 bo rng s dng Timer1 ch 2 thitlp ch baud.



12/17

2. Np thanh ghi TH1 cc gi tr cho trong bng 10.4 thit lp ch baudtruyn d liu ni tip (vi gi thit tn sXTAL= 11.0592MHz).

3. Np thanh ghi SCON gi tr 50H bo ch ni tip 1 ng khung 8 bt dliu, 1 bt Start v 1 bt Stop.

4. Bt TR1 = 1 khi ng Timer1.5. Xo bt TI bng lnh CLR TI6. Byte k t cn phi truyn -c ghi vo SBUF.

7. Bt c TI -c hin th bng lnh JNB TI, xx bo k t -c truynhon tt ch-a.

8. truyn k t tip theo quay tr v b-c 5.V d 10.2 trnh by ch-ng trnh truyn ni tip vi tc 4800 baud. V

d 10.3 trnh by cch truyn lin tc chYES.V d 10.2:

Hy vit ch-ng trnh cho 8051 truyn ni tip mt k t A vi tc 4800 baud lin tc.Li gii:

MOV TMOD, #20H ; Chn Timer1, ch 2 (tng np li)MOV TH1, # 6 ; Chn tc 4800 baud

MOV SCON, #A ; Truyn 8 bt d liu, 1 bt Stop cho php thuSETB TR1 ;Khi ng Timer1AGAIN: MOV SBUF, #A ; Cn truyn k tAHERE: JNB TI, HERE ; Ch n bt cui cng

CLR TI ; Xo bt TI cho k tktipSJMP AGAIN ; Tip tc gi li ch A

V d 10.3:Hy vit ch-ng trnh truyn chYES ni tip lin tc vi tc 9600

baud (8 bt d liu, 1 bt Stop).Li gii:

MOV TMOD, #20H ; Chn b Timer1, ch 2

MOV TH1, # 3 ; Chn tc 9600 baudMOV SCON, #50H ; Truyn 8 bt d liu, 1 bt Stop cho php thuSETB TR1 ;Khi ng Timer1

AGAIN: MOV A, #"Y" ; Truyn k tYACALL TRANSMOV A, #"E" ; Truyn k tEACALL TRANSMOV A, #"S" ; Truyn k tSACALL TRANSSJMP AGAIN ; Tip tc

; Ch-ng trnh con truyn d liu ni tip.TRANS: MOV SBUF, A ; Np SBUFHERE: JNB TI, HERE ; Ch cho n khi truyn bt cui cng

CLR TI ; Ch sn cho mt byte ktipRET10.3.4.1 Tm quan trng ca c TI.

hiu tm quan trng ca c ngt TI ta hy xt trnh t cc b-c d-i ym 8051 phi thc hin khi truyn mt k t quan -ng TxD:

1. Byte k t cn phi truyn -c ghi vo SBUF.2. Truyn bt Start3. Truyn k t 8 bt ln l-t tng bt mt.4. Bt Stop -c truyn xong, trong qu trnh truyn bt Stop th c TI -c bt

(TI= 1) bi 8051 bo sn sng truyn k t k tip.



13/17

5. Bng vi hin th c TI ta bit chc rng ta khng np qu vo thanh ghi SBUF.Nu ta np mt byte vo SBUF tr-c ghi TI -c bt th phn d liu ca bytetr-c ch-a truyn ht s b mt. Hay ni cch khc l 8051 bt c TI khi truynxong mt byte v n sn sng truyn byte k tip.6. Sau khi SBOF -c np mt byte mi t c nhm c th truyn byte mi

ny.T phn trnh by trn y ta kt lun rng bng vic kim tra bt c ngt TI ta

bit -c 8051 c sn sng truyn mt byte khc khng. Quan trng hn cn phini y l bt c TI -c bt bi t 8051 khi n hon tt vic truyn mt byte dliu, cn vic xo n th phi -c lp trnh vin thc hin bng lnh CLR TI. Cngcn l-u rng, nu ta ghi mt byte vo thanh ghi SBUF tr-c khi c TI -c bt th sc nguy c mt phn d liu ang truyn. Bt c TI c th kim tra bng lnh JNBTI hoc c th s dng ngt nh- ta s thy trong ch-ng 11.10.3.5 Lp trnh 8051 nhn d liu.

Trong lp trnh ca 8051 nhn cc byte k t ni tip th phi thc hin ccb-c sau y.

1. Np gi tr 20H vo thanh ghi TMOD bo s dng b Timer1, ch 2 (8btm, t ng np li) thit lp tc baud.

2. Np TH1 cc gi tr cho trong bng 10.4 to ra tc baud vi gi thitXTAL= 10.0592MHz.3. Np gi tr 50H vo thanh ghi SCON bo s dng ch truyn ni tip 1 l

d liu -c ng gi bi 8 bt d liu, 1 bt Start v 1 bt Stop.4. Bt TR1 = 1 khi ng Timer1.5. Xo c ngt RI bng lnh CLRRI6. Bt cRI -c hin th bng lnh JNBRI, xx xem ton b k t -c

nhn ch-a.7. Khi RI -c thit lp th trong SBUF c 1 byte. Cc ni dung ca n -c

ct l-u vo mt ni an ton.8. nhn mt k t tip theo quay tr v b-c 5.

V d 10.4:Hy lp trnh cho 8051 nhn cc byte d liu ni tip v t chng vo cngP1. t tc baud l 4800, 8 bt d liu v 1 bt Stopl.Li gii:

MOV TMOD, #20H ; Chn b Timer1, ch 2 (tng np li)MOV TH1, # 6 ; Chn tc 4800 baudMOV SCON, #50H ; Chn khung d liu 8 bt Stop, bt.SETB TR1 ;Khi ng b Timer1

HERE: JNB R1, HERE ; i nhn ton b l tvo htMOV A, SBUF ; L-u ct k tvo thanh AMOV P1, A ; Gi ra cng P.1CLR RI ; Sn sng nhn byte ktipSJMP HERE ; Tip tc nhn d liu

V d 10.5:Gi s cng ni tip ca 8051 -c ni vo cng COM ca my tnh IBM CP

v m ang s ch-ng trnh Termina. Exe gi v nhn d liu ni tip. Cng P1 vP2 ca 8051 -c n ti cc LED v cc cng tc chuyn mch t-ng ng. Hyvit mt ch-ng trrnh cho 8051.a) Gi thng bo We Are Ready (chng ti sn sng) ti my tnh PC.



14/17

b) Nhn bt k d liu g -c PC gi n v chuyn n cc n LED ang ni ncc chn ca cng P1.c) Nhn d liu trn cc chuyn mch -c ni ti P2 v gi n ti my tnh PC nitip. Ch-ng trnh phi thc hin mt ln a), nh-ng b) v c) chy lin tc vi tc 4800 baud.Li gii:

ORG 0

MOV P2, #0FFH ; Ly cng P2 lm cng voMOV TMOD, #20H ; Chn b Timer1, ch 2 (tng np li)MOV TH1, # 0FAH ; Chn tc 4800 baudMOV SCON, #50H ; To khung d liu 8 bt, 1bt Stop cho php

REN.SETB TR1 ;Khi ng b Timer1MOV DPTR, #MYDATA ; Np con tr n thng bo

H 1: CLR AMOVC A, A + DPTR ; Ly k tJZ DPTR ; Nu k tcui cng mun gi raACALL SEND ; Nu ch-a th gi ch-ng trnh con SENDINC DPTR ; Chy tipSJMP H 1 ; Quay li vng lp

B 1: MOV A, P2 ; c d liu trn cng P2ACALL RECV ; Truyn n ni tipACALL RECV ; Nhn d liu ni tipMOV F1, A ; Hin th n ra cc n LEDSJMP B 1 ;li vng lp v hn

; Truyn d liu ni tip ACC c d liuSEND: MOV SBUF, A ; Np d liuH 2: JNB TI, H 2 ;li vng lp v hn

CLR TI ; Truyn d liu ni tipRET ; Nhn d liu

; Truyn d liu ni tip ACC c d liuRECV: JNB RI, RECV ; Np d liu

MOV A, SBUF ;li y cho n khi gi bt cui cngCLR RI ; Sn sng cho k tmiRET ; Trv mi gi

; Nhn d liu ni tip trong ACCRECV: JNB RI, RECV ; i y nhn k t

MOV A, SBUF ; L-u n vo trong ACCCLR RI ; Sn sng nhn k tm tip theoRET ; Trv ni gi

; Ngn xp ch-a thng boMYDATA: DB Chng ti sn sng 0

END

10.3.5.1 Tm quan trng ca c RT.Khi nhn cc bt quan chn RxD ca n th 8051 phi i quan cc b-c sau:

1. N nhn bt Start bo rng bt sau n l bt d liu u tin cn phi nhn.

P1TxD

RxDP2

ToPC

COMport

8051

SW

LED



15/17

2. K t 8 bt -c nhn ln l-t tng bt mt. Khi bt cui cng -c nhn thmt byte -c hnh thnh v t vo trong SBUF.3. Khi bt Stop -c nhn th 8051 bt RT= 1 bo rng ton b k t -cnhn v phi ly i tr-c khi n b byte mi nhn v ghi ln.4. Bng vic kim tra bt cRI khi n -c bt ln chng ta bit rng mt k t -c nhn v ang nm trong SBUF. Ti sao ni dung SBUF vo ni an tontrong mt thanh ghi hay b nh khc tr-c khi n b mt.

5. Sau khi SBUF -c ghi vo ni an ton th cRI -c xo v 0 bng lnhCLRRI nhm cho cc k t k tip nhn -c -a vo SBUF. Nu khng lm-c iu ny th gy ra mt k t va nhn -c.

T m t trn y ta rt ra kt lun rng bng vic kim tra cRI ta bit 8051 nhn -c mt byte k t ch-a hay ri. Nu ta khng sao -c ni dung ca thanhghi SBUF vo ni an ton th c nguy c ta b mt k t va nhn -c. Quan trnghn l phi nh rng cRI -c 8051 bt ln nh- lp trnh vin phi xo n bng lnhCLRRI. Cng nn nh rng, nu ta sao ni dung SBUF vo ni an ton tr-c khiRI -c bt ta mo him sao d liu ch-a y . Bt cRI c th -c kim trabi lnh JNBRI, xx hoc bng ngt s -c bn ch-ng 11.10.3.6 Nhn i tc baud trong 8051.

C hai cch tng tc baud truyn d liu trong 8051.1. S dng tn s thch anh cao hn.2. Thay i mt bt trong thanh ghi iu khin cng sut PCON (Power Control)nhch ra d-i y.

Ph-ng n mt l khng thc thi trong nhiu tr-ng hp v tn s thch anhca h thng l c nh. Quan trng hn l n khng kh thi v tn s thch anh mikhng t-ng thch vi tc baud ca cc cng COM ni tip ca IBM PC. Do vy,ta s tp trung thm d ph-ng n hai, c mt cch nhn i tn s baud bng phn

mm trong 8051 vi tn s thch anh khng i. iu ny -c thc hin nh thanhghi PCON, y l thanh ghi 8 bt. Trong 8 bt ny th c mt s bt khng -c dng iu khin cng sut ca 8051. Bt dnh cho truyn thng l D7, bt SMOD (ch ni tip serial mode). Khi 8051 -c bt ngun th bt SMOD ca thanh ghi PCON mc thp 0. Chng ta c th t n ln 1 bng phn mm v do vy nhn i -c tc baud. Th t cc lnh -c s dng thit lp bt D7 ca PCON ln cao nh- sau(thanh ghi PCON l th nh a ch theo bt).

MOV A, PCON ; t bn sao ca PCON vo ACCSETB ACC.7 ; t D7 ca ACC ln 1.MOV PCON, A ; By gi SMOD = 1 m khng thay i bt k bt no khc.

bit tc baud -c tng ln gp i nh- th no bng ph-ng php nyta xt vai tr ca bt SMOD trong PCON khi n l 0 v 1.a) Khi SMOD = 0.

Khi SMOD= 0 th 8051 chia 1/12 tn s thch anh cho 32 v s dng n chob Timer1 thit lp tc baud. Trong tr-ng hp XTAL= 11.0592MHz th ta c:

Tn s chu trnh my kHz6.92112

MHz0592.11== v Hz800.28

32

kHz6.921= v SMOD=

0.

SM0D GF0 GF0 PD IDL

D7 D0



16/17

y l tn s -c Timer1 s dng t tc baud. y l c s cho tt cv d t tr-c n gi v n l gi tr mc nh ca 8051 khi bt ngun. Cc tc baud i vi SMOD= 0 -c cho trong bng 10.4.b) Khi SMOD = 1.

Vi tn s c nh thch anh ta c th nhn i tc baud bng cch t btSMOD= 1. Khi bt D7 ca PCON (bt SMOD) -c -a ln 1 th 1/12 tn sXTAL-c chia cho 16 (thay v chia cho 32 nh- khi SMOD= 0) v y l tn s -c

Timer dng thit lp tc baud. Trong tr-ng hp XTAL= 11.0592MHz ta c:

Tn s chu trnh my kHz6.92112

MHz0592.11== v kHz600.57

16

kHz6.921= v

SMOD= 1.y l tn s m Timer1 dng t tc baud. Bng 10.5 l cc gi tr cn

-c np vo TH1 cng vi cc tc baud ca 8051 khi SMOD= 0 v 1.Bng 10.5: So snh tc baud khi SMOD thay i.

Tc baudTH1 (thp phn) TH1 (Hex)SMOD = 0 SMOD = 1

3

61224

FD

DAF4E8

9600

480024001200

19200

960048002400

V d 10.6:gi s tn sXTAL= 11.0592MHz cho ch-ng trnh d-i y, hy pht biu

a) ch-ng trnh ny lm g? b) hy tnh ton tn s -c Timer1 s dng t tc baud? v c) hy tm tc baud truyn d liu.

MOV A, PCON ; Sao ni dung thanh ghi PCON vo thanh ghi ACCSETB ACC.7 ; t D7 = 0MOV PCON, A ; t SMOD = 1 tng gp i tn s baud vi tn s XTAL c nh

;MOV TMOD, #20H ; Chn b Timer1, ch 2, tng np liMOV TH1, 3 ; Chn tc baud 19200 (57600/3=19200) v SMOD = 1

;MOV SCON, #50H ; ng khung d liu gm 8 bt d liu, 1 Stop v cho php RI.SETB TR1 ;Khi ng Timer1MOV A, #B ; Truyn k tB

A1: CLR TI ;Khng nh TI = 0MOV SBUF, A ; Truyn n

H1: JNB TI, H1 ; Chy cho n khi bt cui -c gi iSJMP A1 ; Tip tc gi B

Li gii:a) Ch-ng trnh ny truyn lin tc m ASCII ca chB ( dng nh phn l 01000010)b) Vi tn sXTAL= 11.0592MHz v SMOD= 1 trong ch-ng trnh trn ta c:

11.0592MHz/12=921.6kHz l tn s chu trnh my921.6kHz/16= 57.6kHz l tn s -c Timer1 s dng t tc baud

c) 57.6kHz/3= 19.200 l tc cn tmV d 10.7:

Tm gi tr TH1 ( dng thp phn v hex) t tc baud cho cc tr-nghp sau.



17/17

a) 9600 b) 4800 nu SMOD= 1 v tn sXTAL= 11.0592MHzLi gii:

Vi tn sXTAL= 11.0592MHz v SMOD= 1 ta c tn s cp cho Timer1 l57.6kHz.a) 57.600/9600 =6 do vy TH1 = 6 hay TH1 =FAHb) 57.600/4800 = 12 do vy TH1 = 12 hay TH1 =F4H

V d 10.8:Hy tm tc baud nu TH1 = 2, SMOD = 1 v tn s XTAL =

11.0592MHz. Tc ny c -c h tr bi cc my tnh IBM PC v t-ng thchkhng?

Li gii:Vi tn sXTAL= 11.0592MHz v SMOD= 1 ta c tn s cp cho Timer1 l

57.6kHz. Tc baud l 57.600kHz/2=28.800. Tc ny khng -c h tr bicc my tnh IBM PC v t-ng thch. Tuy nhin, PC c th -c lp trnh truynd liu vi tc nh- vy. Phn mm ca nhiu modem c th lm cho iu ny vHyperterminal ca Windows 95 cng c th h tr tc ny v cc tc khc na.10.3.7 Truyn d liuda trn cc ngt.

Ta phi thy rng tht lng ph cc b vi iu khin phi bt ln xung ccc TI v RI. Do vy, tng hiu sut ca 8051 ta c th lp trnh cc cng truynthng ni tip ca n bng cc ngt. y chnh l ni dung chnh s bn lun ch-ng 11 d-i y.

XTALoscillator

12 28800Hz921.6kHz

16

32

57600Hz

SMOD=0

SMOD=1

28800Hz

11.0592MHz Totimer1to setbaudrate


Documents

Chuong 10_Truyen Thong Noi Tiep - Smith.N Studio