1-Wire (Protocol)

Company: Dallas Semiconductor/Maxim

Linus Won
What is it?
Protocol: to diitally communicate o!er t"isted-pair ca#le "it$ 1-Wire components o!er a 1-Wire
net"or%
net"or% is de&ined "it$ an open-drain ("ired-'(D) master/sla!e multidrop arc$itecture "it$ resistor
pull-up to a nominal )* supply at t$e master
1-Wire net+s , components:
1- a #us master "it$ controllin so&t"are (e-- .M/01 i2utton !ie"er)
3- "irin and associated connectors
,- 1-Wire de!ices
Features/Benefits
eac$ 1-Wire sla!e $as stored in 45M a uni6ue 78-#it serial num#er t$at acts as its node address
de!ice to #e indi!idually selected &rom amon many t$at can #e connected to t$e same #us "ire
o .$is lo#ally uni6ue address is composed o& ei$t #ytes di!ided into t$ree main sections-
Startin "it$ t$e LS29 t$e &irst #yte stores t$e :-#it &amily codes t$at identi&y t$e de!ice type-
.$e next six #ytes store a customi;a#le 8:-#it indi!idual address- .$e last #yte9 t$e most
sini&icant #yte (MS2)9 contains a cyclic redundancy c$ec% (C4C) "it$ a !alue #ased on t$e
data contained in t$e &irst se!en #ytes- .$is allo"s t$e master to determine i& an address "as read
"it$out error- Wit$ a 3
8:
serial num#er pool9 con&lictin or duplicate node addresses on t$e net
are ne!er a pro#lem-
1-Wire de!ices can #e &ormatted "it$ a &ile directory li%e a &loppy dis% &iles can #e randomly
accessed and c$aned "it$out distur#in ot$er records
Maximum data security can #e pro!ided #y 1-Wire c$ip implementation o& t$e <S o!ernment-certi&ied
Secure =as$ 'lorit$m (S='-1)
uses a sinle "ire (plus round) to accomplis$ #ot$ communication and po"er transmission-
' sinle #us master can &eed multiple sla!es o!er a sinle t"isted-pair ca#le
simpli&y desin "it$ an inter&ace protocol t$at supplies control9 sinalin9 and po"er o!er a sinle-"ire
connection-
About the Protocol
1-Wire protocol uses con!entional CM5S/..L loic le!els (maximum >-:* &or loic ?;ero@ and a
minimum 3-3* &or loic ?one@) "it$ operation speci&ied o!er a supply !oltae rane o& 3-:* to 7*-
2ot$ master and sla!es are con&iured as transcei!ers permittin #it se6uential data to &lo" in eit$er
direction9 #ut only one direction at a time ($al&duplex)A Master initiates and controls all de!ices
Data is #yte-se6uential and #it-se6uential "it$ data read and "ritten least sini&icant #it (LS2) &irst
sinal is trans&erred in time slots
System cloc% is not re6uiredA eac$ 1-Wire part is sel&-cloc%ed #y an internal oscillator sync$roni;ed to
t$e &allin ede o& t$e master
4 basic protocol operations:
($ttp://"""-maxim-ic-com/appnotes-c&m/appnoteBnum#er/)33/ln/en 'pp137)
'll de!ice commands are #uilt o&& t$eseC
Li#raries implementin t$ese and $i$er order &unctions a!aila#le-
Typical 1-Wire Communication Flow
.$e &irst part o& any communication in!ol!es t$e #us master issuin a ?reset@ "$ic$ sync$roni;es t$e entire #us-
' sla!e de!ice is t$en selected &or su#se6uent communications- .$is can #e done #y selectin all sla!es9
selectin a speci&ic sla!e (usin t$e serial num#er o& t$e de!ice)9 or #y disco!erin t$e next sla!e on t$e #us
usin a #inary searc$ alorit$m- .$ese commands are re&erred to collecti!ely as ?net"or%@ or 45M (4ead-
5nly-Memory) commands- 5nce a speci&ic de!ice $as #een selected9 all ot$er de!ices drop out and inore
su#se6uent communications until t$e next reset is issued-
5nce a de!ice is isolated &or #us communication t$e master can issue de!ice-speci&ic commands to it9 send data
to it9 or read data &rom it- 2ecause eac$ de!ice type per&orms di&&erent &unctions and ser!es a di&&erent purpose9
eac$ $as a uni6ue protocol once it $as #een selected- /!en t$ou$ eac$ de!ice type may $a!e di&&erent
protocols and &eatures9 t$ey all $a!e t$e same selection process and &ollo" t$e command &lo" as seen in Diure
1 (a#o!e)-
ow power is supplie! in the most common cases ("/ diarams)
, primary "ays:
Sourcin po"er "$ene!er t$e line is a#o!e ,-)*-
o Since 1-Wire de!ices can operate "it$ a ,* supply9 t$e enery a!aila#le #et"een t$e #us supply
le!els o& ,-)* and )* can #e tapped-
o e6ui!alent to operatin t$e load in s$unt mode (permanently across t$e #us9 or pre&era#ly under
#us master control)
"Powerin# metho!s continue!$
Sourcin po"er "$en line is $i$ #y trans&errin c$are to a capacitor (or rec$area#le #attery) t$rou$
a #loc%in diode
o Durin idle periods "$en t$e #us is at )*9 t$e circuit Esteals+ po"er &rom t$e line to c$are t$e
capacitor and po"er t$e load-
o Disad!: adds #ot$ capaciti!e load and lea%ae t$at reduce t$e rane and capa#ility o& t$e 1-Wire
net"or%- Can &ix #y can #e isolatin it #et"een t"o addressa#le s"itc$es controlled #y t$e line
master-
o 'd!: simple and economicalA used internally #y 1-Wire de!ices
Parasitic po"er:
concept o& FstealinF po"er &rom t$e net #y a $al&-"a!e recti&ier
W$en data line is pulled $i$9 t$e diode in t$e $al&-"a!e recti&ier turns on and c$ares an
on-c$ip capacitor-
W$en t$e !oltae on t$e net drops #elo" t$e !oltae on t$e capacitor9 t$e diode is re!erse
#iased9 "$ic$ isolates t$e c$are- .$e resultin c$are pro!ides t$e enery source to
po"er t$e sla!e durin t$e inter!als "$en t$e net is pulled lo"- .$e amount o& c$are lost
durin t$ese periods is replenis$ed "$en t$e data line returns $i$-
Sourcin po"er "it$ a stron pull-up durin idle communication time-
o can #e accomplis$ed #y usin a M5SD/. to pull t$e #us directly to t$e rail
o /-- DS1:S3>-P'4 (diital t$ermometer9 durin temperature con!ersions)
$ttp://pd&ser!-maxim-ic-com/arpd&/DS1:S3>-P'4-pd&

$ttp://"""-maxim-ic-com/appnotes-c&m/appnoteBnum#er/G8G/ln/en ('pp18H: Supplyin po"er !ia 1-"ire #us)
$ttp://"""-maxim-ic-com/appnotes-c&m/appnoteBnum#er/:)H/ln/en ('pp18:: Iuidelines &or 4elia#le 1-"ire
net"or%s)
%ome Topolo#ies
(see $ttp://"""-maxim-ic-com/appnotes-c&m/appnoteBnum#er/)3,/ln/en)
&eneral Ways to Communicate
So&t"are met$ods !ia microprocessor: 1-Wire 'PJ &or Windo"s (.M/0)9 1-Wire C5M inter&ace
(5WC5M)9 1-Wire Pu#lic Domain (PD)9 and 1-Wire 'PJ &or Ka!a1 (5W'PJ)
a prede&ined 1-Wire master c$ip in *erilo and *=DL
DS38:>2 Serial 1-Wire Line Dri!er to communicate "it$ any <'4.
DS18:1 pro!ides a 1-Wire master "it$ a parallel inter&ace-
($ttp://"""-maxim-ic-com/appnotes-c&m/appnoteBnum#er/)33/ln/en last pae)
Closin# 'emar(s
DSG>G1L 1-Wire MicroL'( /!aluation Lit
o $ttp://"""-maxim-ic-com/6uic%B!ie"3-c&m/6!Bp%/3GH,
o M8G->>
o examples: Windo"/door monitor9 .emperature loer9 Simulated room temperature control9 2urlar alarm system
,H 1-Wire de!ices9 8: i2uttons and accessories (sensors9 cloc%s9 adapters9 memory9 etc-)
N $ttp://"""-maxim-ic-com/1-Wire (main pae)
$ttp://"""-maxim-ic-com/appnotes-c&m/appnoteBnum#er/1HG7/ln/en (o!er!ie")
$ttp://"""-maxim-ic-com/appnotes-c&m/appnoteBnum#er/11:G/ln/en ('pp318: <sin a <'4. to Jmplement a
1-Wire 2us Master)
$ttp://"""-maxim-ic-com/appnotes-c&m/appnoteBnum#er/:))/ln/en ('pp1)): o!er!ie" and selection uide to
a!aila#le 'PJs/resources &or communicatin "it$ t$e !ariety o& de!ices)
N $ttp://"""-maxim-ic-com/anBprodline3-c&m/prodline/31 ('LL 'pplication (otes and .utorials &or 1-Wire
de!ices)
N $ttp://"""-maxim-ic-com/appnotes-c&m/appnoteBnum#er/)3,/ln/en ('pp1,3: Ouic% Iuide to 1-Wire net
<sin PCs and Microcontrollers)
$ttp://"""-#rianlane-com/diitemp-p$p (?Dii.emp is a simple to use inter&ace to t$e Dallas Semiconductor
DS1:S3> (DS1:S3>-P'4)9 DS1:339 (DS1:33-P'4) and DS1:23> (DS1:23>-P'4) diital temperature
sensors@)