Understand the ZigBee Spec

8/10/2019 Understand the ZigBee Spec

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Understand the ZigBee spec, from A to Z

From design through certification, following the steps set out by the Alliance can made adesigner's job a lot easier.By Jon Adams, Freescale emiconductor

!ireless "et #esign$ine%&()*(+&& -&& A /#01Building wireless into an application isn't a simple thing2it ta3es an understanding ofradio performance, propagation, modulation, coding, protocol, and more to ma3e a goodwireless lin3. 4t's no wonder that so many designers throw up their hands in despair whenattempting to get rid of a simple serial connection. Until recently, the wireless choiceswere either e5pensi6e, proprietary, and ill7suited to the de6eloper's need, or lesse5pensi6e, proprietary, with no hope of broader interoperability, etc. 8owe6er, ZigBeeand 4/// 9&+.).: may put an end to those problems.

0he ZigBee Alliance is a rapidly growing, open alliance of o6er );& companies that ha6ea common goal, namely cost7effecti6e, simple, ubi+& or less. imple means that the time it ta3es from idea to engineering sample ismeasured in wor37wee3s, not wor37years. And ubi


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1. ZigBee technology sits on top of the IEEE radio.

4/// 9&+.).: is the undercarriage of the ZigBee 6ehicle, so ZigBee networ3ing countson the 4/// standard to deli6er the robustness and reliability that one e5pects from a

wireless networ3. #e6eloped to be a low7duty cycle, ac3nowledgement7based protocol,the spec brings together multiple @F channels in the 9;97, *)7, and +:&&78 bands.!hile the lower bands ha6e some attracti6e performance characteristics, it's the +:&&78 band that attracted the most interest, not only because of the worldwide a6ailabilityof that band for unlicensed operation, but also because of the performance of the productsde6eloped for that band (Fig. 2).

2. Shown are the available channels and the nlicensed natre of each band..

ZigBee wireless technology ta3es ad6antage of the robustness inherent in the 4/// radioand layers upon it a strong mesh networ3 that can self7form and self7heal, route messages


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specific physical de6ice 4(s. 0hese two documents, a6ailable to the general public,pro6ide the core of what the de6ice needs to do to be considered a ZigBee product.

esigning a ZigBee prod!ct

As an e5ample design, let's choose a battery7operated, remote7control light pad with one

push button for the home controls space. "ote that the de6ice uses the imple Bindingprocess. 4n the @= de6ice document %Figure ;b1 we disco6er that the nff@= clusterhas an attribute called nff, with three possible data 6alues. &5&& specifies FF, &5FFspecifies ", and &5F& means 0CC$/ %if it was on, turn it off, and 6ice76ersa1. For thesimple light switch, we'll use only the 0CC$/ 6alue, because we'6e only got amomentary switch on a faceplate. 0he code will issue a ZigBee pac3et that specifies the=luster 4# of &5)D and a data 6alue of &5F& e6ery time the button is pushed (Fig. !).

!. "a#en fro$ the %&' rofile doc$ent this figre diagra$s the S*& device with the

$andatory and optional interfaces.

According to the specification %paragraph ).:.+.+ /nd #e6ice Bind 6er6iew1, simplebinding means- ?ro6ides the ability for an application to support Esimple bindingE whereuser inter6ention is employed to identify command(control de6ice pairs. 0ypical usagewould be where a user is as3ed to push buttons on two de6ices for installation purposes.

0his is an intuiti6e method of binding and one that's used in many applications. 4n ourlight7switch product, this method may be cast as an instruction to the user- E8old downthe button on the remote light switch for fi6e seconds, then push the bind button on themaster home controller within ;& seconds.E 0here could also be other physicalinstantiations of the re


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0he binding comes from user physical input to both the de6ice that can issue thecommand %the switch1 and the de6ice that will respond to the command %the loadcontrol1. 0his binding information will then be stored, at a minimum, in the ZigBeecoordinator assigned to the networ3, and may also be stored in the end de6ices as afallbac3.

eeping the tas3 as straightforward and simple as practical, you may choose to start withsomeone else's ZigBee =ompliant ?latform, where they'6e already demonstrated to theAlliance that the silicon platform with the appropriate software meets the Alliance'stechnical specification re


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number and as long as the Alliance has proof from the test house that the product passedthe certification testing and the de6eloper has demonstrated interoperability at least at oneZigFest, the Alliance can issue authoriation for logo usage.

Because it's a wireless de6ice, the de6eloper must also ensure that it meets the radio

regulatory rules for the countries in which it'll be sold or used. For the U.. and =anada,that means at a minimum getting transmitter testing done at an F==(4=7certified testhouse. Fortunately for the de6eloper, the ZigBee7authoried test houses are alsoregulatory type7certification test houses, as are many other companies. 0his testing isgenerally lengthier than the ZigBee certification testing, but for a simple de6ice, notmuch more so. 0his testing is a re


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defines the ma5imum number of nodes in a gi6en Zigbee networ3. 4n an e5amplenetwor3 where $ma5 H D, =ma5 H +& and @ma5 H ;, a designer can ha6e a total of 9;)nodes. 0here is no limit defined to $ma5, =ma5 and @ma5 e5cept that "total cannote5ceed appro5imately +);.

4n a networ3 with $ma5 H ;, =ma5 H ; and @ma5 H ;, all children may be routers. 0hema5imum number of nodes in the networ3 e5ceeds ,&&&. 0he physical radius of thenet7e6en assuming only )& meters per hop7could be )+& meters, or about :&& feet,potentially co6ering many acres of office or factory floor.

For a networ3 described by $ma5 H )&, =ma5 H ;& and @ma5 H +, where there are a lotof sensors and a well7placed routing infrastructure, the ma5imum number of nodes is wello6er ;),&&&. "etwor3s that are physically larger than this are generally bro3en intomultiple subnetwor3s, just as 4nternet addresses are di6ided into subdomains, partially forease of use and also for added robustness and networ3 capacity.

!hile an initial networ3 address allocation creates a default tree networ3, 6ery soonafterward the networ3 routing de6ices begin to learn additional routes among themsel6es.4n this manner Zigbee nets create a mesh networ3 that may actually do the majority of therouting, depending on routing performance.

Because of the topology of a mesh networ3, latency 6aries depending on the number ofhops re


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Understand the ZigBee Spec

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