B NH THI : TIMER_A1.Tng qut b nh thi ca dng MSP430. -Dng MSP430 c th s dng nhiu b nh thi khc nhau nh: Watchdog Timer: Chc nng chnh l bo v h thng chng trc trc nhng cng c th s dng nh b m thi gian nu chc nng bo v khng cn thit. Basic Timer 1: N cung cp xung nhp ca ng h ,cng nh m khong thi gian. Timer _A: Cung cp trong tt c cc thit b ,n linh hot hn so vi cc b nh thi tnh gi n gin.N c th x l u vo bn ngoi v kt qu u ra trc tip o tn s ,du thi gian u vo v u ra a chnh xc quy nh thi gian ,hoc 1 ln hoc nh k.C kt ni ni b khc mo dun n c th o lng thi gian ca tn hiu t so snh .N cng c th to ngt Timer_B: hot ng hai ch Timer v counter .N cng p ng a chc nng nh Timer_A, cng c kh nng to ngt khi n m trn ,hoc cc thanh ghi capture/so snh. 2.Timer_A. -Chip vi x l MSP430F2121 s dng b nh thi Timer_A . 2.1.c tnh ca Timer_A. -y l b m thi gian c mc ch chung linh hot nht trong MSP430 c dng trong tt c cc thit b. -L b nh thi Timer/Counter 16 bit. -Vi 3 thanh ghi lu tr v 3 thanh ghi so snh . -Timer_A la mt thanh ghi a chc nng : m thi gian ,so snh v PWM.ng thi n cng c kh nng ngt khi counter m trn hoc mi thanh ghi m trn . -Cc c tnh chnh ca Timer_A bao gm:

L mt Timer/counter 16 bit khng ng b vi 4 ch hot ng. C th la chn v cu hnh ngun xung Hai ti 3 thanh ghi c th cu hnh Capture/compare Cu hnh u ra vi ch PWM Cht ng vo v ng ra khng ng b

-S khi ca Timer_A:

2.2.Ch hot ng ca Timer_A. -Timer _A hot ng ch Counter 16 bit.

- ch Counter gi tr thanh ghi TAR tng hoc gim theo cnh ln ca xung clock (ty thuc vo ch hot ng ).Ga tr ca thanh ghi TAR c th c c hoc ghi nh phn mm .N c kh nng to ra mt ngt khi m trn . Thnh ghi TAR c th b xa khi set bit TACLR.Vic set bit TACLR ng thi cng xa gi tr la chn cho b chia xung hoc ch m ln hay m xung . 2.3.La chn ngun xung v b chia xung. -Timer c th la chn ngun xung t ACLK ,SMCLK hoc s dng ngun xung ngoi thng qua TACLK hoc INCLK. -Ngun xung c chn c th c chia 2,4 hoc 8. -B chia xung c reset khi set bit TACLR. 2.4.Kch hot Timer_A. -Timer_A c th c kch hot hoc kch hot li bng cc cch sau: Timer m khi MCx >0 v ngun xung c kch hot . Khi Timer ang hot ng ch m ln hoc m xung .C th dng Timer bng cch ghiTACCR0 =0.Timer s kch hot tr li khi gi tr hgi vo TACCR0 khc 0.Ga tr m ln s bt u t 0. 2.5.Cc ch hot ng ca Timer_A. -Timer_A hot ng 4 ch : ch dng ,ch m ln ,ch lin tc ,ch m ln/xung. -Cc ch ny c la chn bng bit MCx.

Ch dng (MCx=0) :b m thi gian phi dng li.Tt c cc s ng k bao gm c TAR, gi li gi tr ca n c th khi ng li sau n li tt. UP(1): s lng truy cp t 0 n TACCR0 chp/so snh ng k cho knh 0.N tr v 0 cho vic chuyn i tip theo.Up thng c s dng khi tt c cc knh cung cp kt qu u ra cng mt tn s ,thng xuyn iu ch rng xung. Continuous (2): Truy cp chy t do trong phm vi t 0x0000 n 0xFFFF,thun tin nht cho u vo chp cng c s dng khi cc knh cung cp kt qu u ra vi tn s khc nhau hoc khng nh k tt c. Up/down(3): truy cp t 0 n TACCR0,ri m v 0 ri lp i lp li .Thng s dng iu ch xung chiu rng trung tm. 2.6.Cc ngt ca Timer _A. -C hai cch ngt c to ra do Timer_A: Vecter ngt TACCR0 cho TRCCR0 CCIFG. Vector ngt TAIV cho tt c cc c ngt CCIFG khc v TAIFG. -Trong ch lu tr CCIFG c set khi gi tr ca Timer c lu tr do thanh ghi TACCRx. C th s dng phn mm set hoc xa bt k c ngt CCIFG no . Tt c cc c ngt CCIFG yu cu mt ngt khi bit CCIE v GIE c set. -Ngt TACCR0 CCIFG l ngt ca Timer _A c mc u tin cao nht .C ngt TACCR0 CCIFG t ng reset khi ngt TACCR0 c phc v.

2.7.Thanh ghi iu khin Timer_A.

-Thanh ghi iu khin TACTL:

Bit 10 n 15 khng s dng TASSELx (BIT 8 v 9 ) : La chn ngun xung clock : 00 TACLK 01 ACLK 10 11 SMCLK INCLK

IDx (BIT 6 v 7): La chon b chia trc : 00 /1 01 /2 10 /4 11 /8 MCx ( bit4 v 5) :La chn ch hot ng : 00 dng ch 01 ch ln 10 tip tc ch

11 ch ln/xung TACLR Bit 2: Xa Timer _A. Khi bit ny c reset ,gi tr m , gi tr b chia trc u c reset. TAIE Bit 1: Cho php ngt .Khi bit =1 cho php ngt , khi =0 th cm ngt. TAIFG Bit 0 :C ngt ca Timer_A: Bit =0 khng c ngt no ang ch Bit =1 c ngt ang ch phc v. -Thanh ghi Timer_A counter TAR. L thanh ghi 16 bit ,n l trung tm hot ng ca b m thi gian( b m thi gian ng k TAR). N c iu khin bi thanh ghi TACTL. N lm cng vic lp trnh thit lp mt mi quan h gia gi tr trong thi gian truy cp v thc t .iu ny ph thuc ch yu vo tn s ng h cho b m thi gian.N c th la chn t 4 ngun bng cch s dng cc bit TASSELx: +,SMCLK l ni b v thng nhanh ( tc MHz). +,ACLK ni b v thng chm ( khong 32KHz). +,TACLK l bn ngoi. +,INCLK l bn ngoi i khi l m pin ring bit nhng thng c kt ni thng qua bin tn cho TACLK INCLK=TACLK. TAR gia tng trn cc cnh (tch cc) ang ln ca ng h .vic b tr INCLK= TACLK trong nhiu thit b cho php TAR c gim tc (tiu cc). B m thi gian c 4 ch hot ng ,c la chn tng ng vi cc bit MCx nh phn trn trnh by. -Timer_A interrupt vector (TAIV) Msp430 cung cp mt vector ngt TAIV xc nh ngun gc ca ngt nhanh chng . Khi mt hoc nhiu chia s v kch hot c ngt c thit lp ,TAIV c np vi cc gi tr tng ng vi cc m ngun vi cc u tin cao nht .Cc gi tr trong TAIV cho Timer _A3 c lit k trong bng:

Bt k truy cp TAIV t ng reset c TAIV v c tng ng .Nu khc ngt ang ch ,TAIV c np li vi cc gi tr cho ngun vi mc cao nht . -Ngoi ra cn cc thanh ghi khc nh :TACCTL0 ,TACCTL1, TACCTL2 ,TACCR0 ,TACCR1, TACCR2 .