V DS18B20:1. c im v cc thng s: S dng giao din 1-Wire nn ch cn c mt chn ra truyn thng. Gii o nhit: -55C n +125C (sai s 0.5C khi nhit t -10C n 85C) phn gii khi o nhit t 9 n 12 bit Ngun cp t 3.0V n 5.5V v c th cp qua ng d liu. Mi vi mch DS18B20 c m nhn din ln n 64 bit cha trong b nh ROM trn chip, gi tr nh phn c khc bng tia laze, nn nhiu vi mch DS18B20 c th kt ni vo mt bus 1-Wire m khng c s nhm ln. Thi gian chuyn i ti a l 750ms cho m ha 12 bit.S chn:

2. Tng quan:u o nhit DS18B20 a ra s liu biu th nhit o c di dng m nh phn t 9 n 12 bit.S khi ca DS18B20:

M 64 bit trong ROM: Mi cm bin nhit DS18B20 c mt dy m 64 bit duy nht c lu tr trong b nh ROM c khc bng k thut laze.

8 bit u l m nh danh h mt dy, m ca DS18B20 l 28h.48 bit tip theo l m xut xng duy nht, ngha l mi cm bin DS18B20 ch c mt m.8 bit cui c ngha nht l byte m kim tra CRC (cyclic redundancy check), byte ny c tnh ton t 56 bit u tin ca dy m trn ROM. B nh SCRATCHPAD: B nh DS18B20 bao gm 9 thanh ghi 8 bit.

Gii thch:Byte 0 v 1 cha LSB, MSB ca thanh ghi nhit . Byte ny ch c.

Byte 2, 3: cp nht thanh ghi TH v TL, lu gi tr nhit ngng. Byte 4: cha d liu ca thanh ghi cu hnh hot ng ca DS18B20 (Configuration Register)

Byte 5, 6 v 7 khng s dng.Byte 8: thanh ghi ch c v cha m kim tra CRC t byte 0 n byte 7.D liu trong byte 2,3,4 c ghi thng qua lnh Write Scratchpad [4Eh] v d liu c truyn n DS18B20 vi bit LSB ca byte 2, sau khi ghi d liu c th c c li thng qua lnh Read Scratchpad [BEh] v khi c Scratchpad th bit LSB ca byte 0 s c gi i trc tt c cc byte u c c, nhng ch ghi c byte 2,3 v 4. chuyn gi tr TH v TL t b nh vo EEPROM th cn gi lnh Copy Scratchpad [48h] n DS18B20. V d liu t EEPROM cng c th c chuyn vo thanh ghi TH, TL thng qua lnh Recall E2 [B8h].3. Phng thc giao tip:Vic trao i d liu gia VK v DS18B20 thng qua 3 bc: Bc 1: Khi to xung reset v nhn tin hiu hin t DS18B20.Qu trnh khi to bao gm 1 xung reset do VK gi n DS18B20, sau xung presence t DS18B20 gi n VK, bo hiu cho VK bit s hin din ca DS18B20, v qu trnh hot ng trao i d liu c th bt u. Bc 2: Lnh iu khin ROMCc lnh ny lm vic vi m 64 bit trong ROM, lnh ny c pht ra sau qu trnh khi to. Lnh cho php VK bit c bao nhiu thit b v thit b loi g trn bus.C 5 lnh ROM: READ ROM (33h), MATCH ROM (55h), SKIP ROM (CCh), SEARCH ROM (F0h), ALARM SEARCH (ECh).

READ ROM (33h): Cho php c ra 8 byte m khc bng laser trn ROM, bao gm: 8 bit m nh tn linh kin (10h), 48 bit s xut xng, 8 bit kim tra CRC. Lnh ny ch dng khi trn bus c 1 cm bin DS1820, nu khng s xy ra xung t trn bus do tt c cc thit b t cng p ng.MATCH ROM (55h): Lnh ny c gi i cng vi 64 bit ROM tip theo, cho php b iu khin bus chn ra ch mt cm bin DS1820 c th khi trn bus c nhiu cm bin DS1820 cng ni vo. Ch c DS1820 no c 64 bit trn ROM trung khp vi chui 64 bit va c gi ti mi p ng li cc lnh v b nh tip theo. Cn cc cm bin DS1820 c 64 bit ROM khng trng khp s tip tc ch mt xung reset. Lnh ny c s dng c trong trng hp c mt cm bin mt dy, c trong trng hp c nhiu cm bin mt dy.SKIP ROM (CCh): Lnh ny cho php thit b iu khin truy nhp thng n cc lnh b nh ca DS1820 m khng cn gi chui m 64 bit ROM. Nh vy s tit kim c thi gian ch i nhng ch mang hiu qu khi trn bus ch c mt cm bin.SEARCH ROM (F0h): Lnh ny cho php b iu khin bus c th d tm c s lng thnh vin ti ang c u vo bus v cc gi tr c th trong 64 bit ROM ca chng bng mt chu trnh d tm.ALARM SEARCH (ECh): Tin trnh ca lnh ny ging ht nh lnh Search ROM, nhng cm bin DS1820 ch p ng lnh ny khi xut hin iu kin cnh bo trong php o nhit cui cng. iu kin cnh bo y c nh ngha l gi tr nhit o c ln hn gi tr TH v nh hn gi tr TL l hai gi tr nhit cao nht v nhit thp nht c t trn thanh ghi trong b nh ca cm bin.Lu : Nu ta ch thc hin o nhit v hin th nhit n gin vi IC DS18B20 th c th b qua cc lnh: MATCH ROM, SEARCH ROM, ALARM SEARCH, Bc 3: Lnh chc nng DS18B20Sau khi VK nh a ch thit b cn giao tip thng qua cc lnh ROM, VK s gi cc lnh iu khin hot ng ca DS18B20. Nhng lnh ny cho php VK ghi v c d liu t b nh Scratchpad ca DS18B20, bt u qu trnh chuyn i nhit v xc nh ch cp ngun.C 6 lnh chc nng DS18B20: WRITE SCRATCHPAD (4Eh), READ SCRATCHPAD (BEh), COPYSCRATCHPAD (48h), CONVERT T (44h), READ POWER SUPPLY (B4h), RECALL E2 (B8h)WRITE SCRATCHPAD (4Eh): Lnh ny cho php ghi 3 byte d liu vo b nh nhp ca DS1820. Byte u tin c ghi vo thanh ghi TH (byte 2 ca b nh nhp) cn byte th hai c ghi vo thanh ghi TL (byte 3 ca b nh nhp). Byte th 3 c ghi vo thanh ghi cu hnh (byte 4). D liu truyn theo trnh t u tin l bit thp nht u tin. C ba byte ny phi c ghi trc khi thit b ch xut ra mt xung reset hoc khi c d liu khc xut hin.READ SCRATCHPAD (BEh): Lnh ny cho php VK c ni dung b nh nhp. Qu trnh c bt u t bit LSB ca byte 0 v tip tc cho n byte th 9 (byte 8 CRC). Thit b ch c th xut ra mt xung reset lm dng qu trnh c bt k lc no nu nh ch c mt phn ca d liu trn b nh nhp cn c c.COPYSCRATCHPAD (48h): Lnh ny copy ni dung ca 3 thanh ghi TH v TL, cu hnh Configuration (byte 2, byte 3 v byte 4) vo b nh EEPROM.Nu cm bin c s dng trong ch d cp ngun l bt u vic o.CONVERT T (44h): Lnh ny khi ng mt qu trnh o v chuyn i gi tr nhit thnh s (nh phn). Sau khi chuyn i gi tr kt qu o nhit c lu tr trn thanh ghi nhit 2 byte trong b nh nhp. Thi gian chuyn i khng qu 200 ms, trong thi gian ang chuyn i nu thc hin lnh c th cc gi tr c ra u bng 0.READ POWER SUPPLY (B4h): Mt lnh c tip sau lnh ny s cho bit DS1820 ang s dng ch cp ngun nh th no, gi tr c c bng 0 nu cp ngun bng chnh ng dn d liu v bng 1 nu cp ngun qua mt ng dn ring.RECALL E2 (B8h): Lnh ny s ly gi tr ca 2 thanh ghi TH v TL v thanh ghi cu hnh t trong EEPROM ra b nh nhp.Kt ni vi VK v u mch cm bin:

4. Cch c nhit : Bn trong DS18B20 s c b chuyn i nhit sang gi tr s c lu trong cc thanh ghi b nh Scratchpad. phn gii nhit o c th c cu hnh ch 9 bit, 10 bit, 11 bit, 12 bit. ch mc nh th DS18B20 hot ng phn gii 12 bit. bt u qu trnh c nhit , v chuyn i t gi tr tng t sang gi tr s th VK gi lnh CONVERT T [44h], sau khi chuyn i xong th gi tr nhit s lu trong 2 thanh ghi nhit b nh scratchpad (byte 0 v 1) v IC tr v trng thi ngh. Nhit c lu bn trong DS18B20 c tnh nhit Celcius nu tnh nhit Fahrenheit cn phi xy dng thm bng chuyn i nhit . Gi tr nhit lu trong b nh 2 bytes-16bits: s m s c lu di dng b 2. Bit cao nht l bit du (S) nu S=0 th gi tr nhit dng v S=1 th gi tr nhit m. Nu cu hnh phn gii l 12 bits th tt c cc bit u c s dng. Nu phn gii 11 bits th bit 0 khng c s dng. Tng t nu cu hnh l 10 bits th bit 1, 0 khng c s dng, nu cu hnh l 9 bit th bit 2, 1, 0 khng c s dng. Nhit sau khi c lu vo 2 thanh ghi b nh s c so snh vi 2 thanh ghi ngng nhit TH v TL. Cc gi tr ngng c ngi dng quy nh v n s khng thay i khi mt in. Nh vy ch c phn nguyn, cc bit 11-4 ca gi tr nhit c so snh vi thanh ghi ngng. Nu gi tr nhit c v nh hn mc TL hoc ln hn mc TH th c bo qu nhit s c bt ln v n s thay i mi qu trnh c nhit . VK c th kim tra trng thi qu nhit bng lnh ALARM SEARCH [ECh].

Lu lnh ROM

VK Txxung Reset

VK Txlnh ROMDS18B20 Txxung Reset Khi to

Lnh SKIP ROM (CCh)

N

Y

DS18B20 Tx lnh chc nng

Lu cm bin c nhit : Lu chng trnh chnh:

DS18B20 Tx lnh chc nng

c d liu t 2 byte nhit Lnh READ SCRATCHPAD (BEh)Lnh CONVERT T(44h)

Truyn d liu cho thanh ghi SBUFLy d liu t bin lu nhit Khi to Cng ni tipTMOD=0x20hTH1=0xFDhSCON=0x50hTR1=1

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