实践ZigBee：微控制器实现802.15.4协议指南 - CSDN文库

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"Hands On ZigBee——一本关于ZigBee技术的实践指南，由Fred Eady撰写，属于802.15.4标准的微控制器实现介绍，是ZigBee领域的经典读物。" 本文将深入探讨ZigBee技术，这是一种基于IEEE 802.15.4标准的无线通信协议，特别适用于低功耗、低数据速率的设备网络，如智能家居、物联网(IoT)和传感器网络。《Hands On ZigBee》这本书由Fred Eady撰写，它不仅提供理论知识，还强调实践经验，帮助读者了解如何在微控制器上实施ZigBee协议。 ZigBee的核心是IEEE 802.15.4标准，这是一个定义了物理层和媒体访问控制(MAC)层的规范，用于低复杂度、低功耗、低成本的设备。通过使用这个标准，ZigBee能够支持自组织网络，其中设备可以动态地加入或离开网络，形成星型、网状或树形拓扑结构。在书中，作者可能会涵盖以下关键知识点： 1. **ZigBee概述**：解释ZigBee技术的起源、目的和应用领域，以及与蓝牙、Wi-Fi等其他无线技术的区别。 2. **802.15.4标准详解**：深入讨论物理层和MAC层的工作原理，包括传输速率、频道选择、数据包格式和错误检测与纠正机制。 3. **网络架构**：介绍ZigBee网络的三种主要角色——协调器、路由器和终端设备，以及它们在网络中的功能和交互方式。 4. **安全机制**：讲解ZigBee的加密和身份验证过程，如AES-128加密，确保数据在网络中的安全传输。 5. **微控制器编程**：详细阐述如何在微控制器上配置和编程ZigBee堆栈，包括固件开发和调试技巧。 6. **网络建立与管理**：介绍如何创建和管理ZigBee网络，包括设备入网、网络拓扑构建和网络维护。 7. **应用示例**：通过实例展示ZigBee技术在实际项目中的应用，如智能家居自动化、环境监测系统等。 8. **故障排查和优化**：提供解决问题的策略和技巧，以提高网络性能和稳定性。 9. **开发工具和平台**：介绍常用的ZigBee开发工具、软件和硬件平台，如ZigBee开发板和SDK。这本书对想要理解和实践ZigBee技术的工程师、学生或爱好者来说，是一本宝贵的资源。通过学习，读者不仅可以掌握ZigBee的基础知识，还能获得实施和调试ZigBee网络的实际经验。由于ZigBee在物联网领域的广泛应用，掌握这项技术对于从事相关工作的专业人士至关重要。

CHAPTER

1

Speaking the Language

Some famous person once said, "No matter where you go, there you are." No matter where

you may find yourself, it's always a good idea to know how to speak the language. For

instance, when you find yourself in a foreign country, phrases like "Thank you," "Hello"

and "I need to use your bathroom" can come in very handy, depending on the situation. The

same philosophy holds true when it comes to learning about things technical. To that end,

I'm going to take the stance that you are reading this book because you want to know more

about IEEE 802.15.4 and ZigBee. In this chapter, I'm going out one step further and will

work with the pretense that you know absolutely nothing about IEEE 802.15.4 or ZigBee. So,

in my mind, my job is to teach you to speak the language of ZigBee and subsequently IEEE

802.15.4. Once you become familiar with acronyms like PSDU, MPDU, NWK, PAN and

MAC, the rest of the ZigBee puzzle and the underlying IEEE 802.15.4 protocol will begin to

come together more easily for you. You'll need to understand the nuances of ZigBee-speak

and IEEE 802.15.4-speak before we move into the actual hands-on portion of this book.

Otherwise, you and I will just be mindlessly assembling meaningless ZigBee radio building

blocks and crawling through undecipherable C source code.

If you're new to the concept of ZigBee, I want to introduce you to the world of ZigBee the

fight way. So, we'll start at the beginning of ZigBee time. However, first things first. It is re-

quired that you carve the ZigBee international anthem into your memory bank. So, get up out

of that recliner and repeat after me:

ZigBee: Wireless control that simply works.

Say it again, louder:

ZigBee: Wireless control that simply works.

I can't hear your

ZigBee: Wireless control that simply works.

A True Story about a Couple of Flying Bugs

I don't know about you, but for me the ZigBee pledge of allegiance sets the tone within

which ZigBee was initially designed. However, ZigBee wasn't always ZigBee, if you know

what I mean. I actually came across an old Philips presentation dated June 26, 2000 that laid

out the plans for what was then called the Philips RF-Lite Program. Interestingly enough, the

presentation begins with a painting called

The Tower of Babel and in the liner notes there are

Chapter I

associated intellectual comments and interpretations of the Tower of Babel story. Although

I found this to be pretty weird, of course, the idea was to convey that RF-Lite would cut

through the clutter of remote control and existing competitive radio systems of the day.

As you progress through the Philips RF-Lite presentation, the concept of Firefly is present-

ed~yet another protocol, but named after a flying bug. It is strongly believed that ZigBee

is supposedly named for bees doing that zig-zag thing they do that always seems to find the

best flowers and the hive. So, get used to references to flying bugs, particularly the bee.

By the way, ever wonder where lightning bugs (that's what us Southern kids called fireflies)

went during the day?? Well, let me tell you. Those little buggers hide amongst the trees and

vegetation during the day. And, if you think fireflies are docile little creatures that glow for

our delight, get real. These guys come out of the gate eating meat and that glow they produce

is for finding sex in the city. It has been said that if a male flashes the wrong signal, a female

of another species of firefly will descend upon him and, yep, you guessed it, eat him up.)

Firefly was a spin-off of HomeRF-Lite, which was touted as a very low-cost method of low-

speed data transfer that consumed very little power. (Hmmm...keep that low-power definition

of HomeRF-Lite and Firefly in your long-term memory cells, as I guarantee you'll experience

a little dEj~ vu as you continue to learn more about ZigBee and IEEE 802.15.4 networking.)

A Firefly working group was formed and face-to-face quarterly meetings were planned. (Hm-

mmm...as I write this text, a "quarterly" ZigBee Alliance Open House is being held in Seoul,

Korea and a new tactical direction for ZigBee was announced.) The Firefly working group

included some big guns such as Panasonic, Texas Instruments, Honeywell, Invensys, Lego

and Mattel. (Hmmm...Can you say Chipcon...Can you say Texas Instruments...Can you say

Chipcon IEEE 802.15.4 radios now owned by Texas Instruments? You'll also see Panasonic

play a part in IEEE 802.15.4 and ZigBee if you continue to read this little ZigBee book. Hon-

eywell and Invensys are currently ZigBee Alliance members along with Texas Instruments.

Hmmmm...)

Firefly was to be a low-speed product with a data throughput minimum of 10 Kbps and a

maximum throughput of 115.2 Kbps. I can't provide any hardcopy proof that the Firefly

communication link speeds were chosen to interface to and/or replace existing products with

existing RS-232 serial ports, but those Firefly speeds fit nicely within practical minimum and

maximum speeds of a typical RS-232 serial port.

The projected range of Firefly-based products was specified between 10 and 75 meters. Node

count for a Firefly network maxed out at 254 with a maximum of four of what was termed

"critical" devices. Up to 100 Firefly networks could be co-located. The real kicker was that

a Firefly node would cost less than $3.00 and be able to operate up to 2 years before the

Firefly's tail light would go dark.

The license-free ISM band was chosen for Firefly nodes, which would automatically insert

and disassociate themselves in the network as required. Firefly was obviously aimed at indoor/

outdoor use, as the marketing requirements listed RF penetration through walls and ceilings

and home/garden use. To help eliminate interference with other devices operating in the same

Speaking the Language

ISM bandwidth, the Firefly nodes would use DSSS (Direct Sequence Spread Spectrum) tech-

nology and Cartier Sense Multiple Access (CSMA-CA) listen-before-transmit network access.

The Firefly protocol stack looked much like stacks look today. Data from the Firefly radio en-

tered via a PHY (Physical) layer. The Firefly MAC (Medium Access Control) layer accepted

data from the PHY layer and pushed it up to the Firefly DLC (Data Link Control) layer. The

application layer resided inside the Firefly node and was accessed by an external user inter-

face via API (Application Program Interface) calls. The configuration I just described would

have resided in a Firefly slave node. A master Firefly node inserted a NWK (Network) layer

between the DLC layer and the application layer.

As you've already ascertained, a master/slave relationship formed the Firefly network topol-

ogy, with the master node being in direct communication contact with each slave node. This

type of topology creates a virtual peer-to-peer communications link as every node can talk

to every other node in the star as long as the master can pass the messages between the slave

nodes that need to talk to each other.

Meanwhile, there were a number of engineers that had determined that Wi-Fi (the subject

of my previous book) and Bluetooth, which is now trying to come into its own, as everyone

has a B luetooth cell phone interface in their ear, weren't going to cut it in some applications.

What these guys and gals wanted was a self-healing ad hoc network of digital radios that

could organize themselves into a cohesive and orderly network without external intervention.

Simply put, they wanted a working Firefly. However, that was not going to be. The IEEE

was already working on 802.15.4 by this time and the IEEE 802.15.4 standard came to life in

2003 and learned to fly (not glow and fly) in 2004. While all of this IEEE stuff was going on,

the ZigBee Alliance sprouted from the ground in 2002 and it now looks like the ZigBee acorn

is going to be a really big tree. As for the Firefly project, we all know what happens when

fireflies are left in the jar too long.

Ddj, vu

Although Firefly's tail light was glowing more dimly in the jar as each hour passed, many

of the attributes of Firefly would find their way out of that jar and into ZigBee. Remember

this? Firefly was a spin-off of HomeRF-Lite, which was touted as a very low-cost method of

low-speed data transfer that consumed very little power. Well, how about this? ZigBee was

designed as a low-speed means of data transportation, which consumes very little power and

can operate for months or even years on a single battery. When compared with other wireless

communications systems that operate in the license-free ISM band, ZigBee comes in on the

lowball side as far as cost per node is concerned. As you read more and more about ZigBee

and IEEE 802.15.4, think about what you've already read about Firefly. You'll experience

dEjh vu all over again.

The Muhammad Ali of Networks

I'm old. I still remember a young man from Louisville, Kentucky named Cassius Clay who

stunned the world by knocking out a bigger and more powerful Sonny Liston. (Sonny was

Chapter I

later implicated with the Mob. I wonder how much Mob money unexpectedly changed hands

when Sonny's head hit the canvas.) Anyway, time passed and times changed. Cassius became

Muhammad Ali, Sonny was purportedly employed by the Mob after retirement and the newly

crowned king of boxing was to become by his poems an unexpected honorary ZigBee bene-

factor. Muhammad Ali once said (actually, he said it many times), "Float like a butterfly, sting

like a bee." There we go again. Another reference to flying bugs. We all knew what Muham-

mad meant and you can apply his description of his fighting style directly to ZigBee. ZigBee

is a lightweight wireless network protocol that packs a punch.

ZigBee is officially a wireless network protocol that is designed to be used with low-data-

rate sensor and control networks. If a sensor doesn't need to report its condition constantly

and allows the sensor-support electronics and radio to sleep most of the time, that sensor is

what ZigBee was designed for. ZigBee can also eliminate the need to string wires all over

the place, as it can easily reach data rates comparable to and above standard RS-232 and RS-

485 wired protocols. Although an IEEE 802.15.4 network can easily obtain RS-232 speeds,

you won't see many battery-powered applications of IEEE 802.15.4 networks replacing

RS-232 communications links, especially if the traffic on the IEEE 802.15.4-based pseudo-

RS-232 link is heavy. That's not what IEEE 802.15.4 networks or the ZigBee protocol is

designed to do.

Let's get one item of confusion out of the way. ZigBee is not IEEE 802.15.4 and IEEE

802.15.4 is not ZigBee. ZigBee is a standards-based network protocol supported solely by

the ZigBee Alliance that uses the transport services of the IEEE 802.15.4 network specifica-

tion. The ZigBee Alliance is responsible for the ZigBee standard and the IEEE is boss when

it comes to the IEEE 802.15.4 specification. That's no different from TCP/IP using the IEEE

802.1 lb wireless specification to transport IP datagrams and TCP segments between nodes

equipped with 802.1 lb radios. The concept of a network protocol tiding on a specification

is called layering. Thus, ZigBee is layered on top of the IEEE 802.15.4 specification, just as

TCP/IP can be layered over 802.1 l b or 802.3.

The IEEE 802.15.4 specification also uses internal layers, which are normally referred to as

sublayers. The wireless 802.1 l b specification and the wired 802.3 specification also employ

the concept of sublayers. The IEEE 802.15.4 specification calls out a pair of 802.15.4 sublay-

ers, the PHY and the MAC.

The IEEE 802.15.4 standard actually defines not one but two PHYs, which span across three

license-free frequency bands. One PHY spans the 868/915-MHz frequency band and the other

PHY is dedicated to the 2.4-GHz frequency band. The 2.4-GHz frequency band supports a to-

tal of 16 channels numbered 11 to 26. Ten channels beginning with channel 1 and ending with

channel 10 can be found in the 902-to-928-MHz frequency spectrum, which is commonly re-

ferred to as the 915-MHz band. The third license-free RF area, 868 to 870 MHz, only allows

for channel 0. Data rates for each of the frequency domains also differ with the 2.4-GHz band

allowing a maximum data rate of 250 kbps. The 902-to-928-MHz band data rate maximum

is 40 kbps and the single-channel 868 to 870 MHz tops out at 20 kbps. Most everyone that

walks the Earth can use the 2.4-GHz frequency spectrum. Only those that breathe air in North

Speaking the Language

America, Australia, New Zealand, Israel and Europe can operate their ZigBee radios in the

bands below 1 GHz.

If we relate the IEEE 802.15.4 sublayers to the ZigBee protocol stack, the ZigBee PHY

sublayer, which is actually the IEEE 802.15.4 PHY sublayer, is all about the radio and the

generation of the radio link. A ZigBee stack's PHY responsibilities include receiver energy

detection, link quality indication and clear channel assessment. The ZigBee stack's PHY is

also primarily responsible for transmitting and receiving packets across the magnetic me-

dium. The ability to sniff the air for other nodes is very important in the ZigBee and IEEE

802.15.4 world as this is what is done to determine if a new ZigBee or IEEE 802.15.4 net-

work can be spawned.

The IEEE 802.15.4 MAC sublayer is in control of what is happening on the radio link. Again,

relating the IEEE 802.15.4 MAC sublayer to the ZigBee stack, a ZigBee stack's MAC, which

is actually the IEEE 802.15.4 MAC, is in control of the access to the radio channel and em-

ploys the services of CSMA-CA (Cartier Sense Multiple Access - Collision Avoidance) to

avoid collisions on the radio link. Network association and disassociation are also duties that

are handled by the ZigBee stack's MAC sublayer. And, if there is any security being applied

to the radio link, the MAC is in charge of that too. Flow control, the acknowledgment and re-

transmission of data packets, frame validation and network synchronization falls on the IEEE

802.15.4 MAC sublayer in addition to everything else I've already mentioned. If all of that is

not enough work for the MAC, it is also a key player in making sure the upper layers of the

ZigBee stack get exactly what they require for proper application operation and data transfer.

If you had the chance to read my previous books on Ethernet networking, you know that we

dealt with packet sizes that could extend beyond one thousand bytes. The maximum number

of bytes we'll have to deal with in a ZigBee packet is only 127 and that includes the 16 bits

of CRC (Cyclic Redundancy Check). The CRC has another name:

checksum.

The CRC bits

make up a checksum value that is intended to help verify the integrity of the contents of the

ZigBee or IEEE 802.15.4 packet. The IEEE 802.15.4 standard also includes an optional ac-

knowledged data mode that allows any ZigBee or IEEE 802.15.4 network frame that has the

ACK flag set to have its receipt acknowledged by the receiver. This is a good way to know if

the frame has been received or not, but it doesn't guarantee that the frame will be processed

by the receiver. The idea of the acknowledged frame is to continue to retry to deliver the

frame after a defined timeout period. An error is declared if the frame is not acknowledged

after a predefined number of delivery attempts. If the full packet addressing scheme is em-

ployed, the maximum amount of actual data a ZigBee packet can contain is 102 bytes.

ZigBee Devices

Before we can talk about how ZigBee networks can be configured, we must first under-

stand who the ZigBee network players are and how they relate to IEEE 802.15.4. The IEEE

802.15.4 specification identifies two devices. They are the FFD and RFD. The 802.15.4 Full

Function Device (FFD) is literally able to do it all. A typical FFD found in a ZigBee net-

work will be powered from an inexhaustible power source, which is called out as an AC-fed

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