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AN1066

INTRODUCTION

Implementing applications with wireless networking is

now common. From consumer devices to industrial

applications, there is a growing expectation that

devices will have built-in the ability to communicate

with each other without a hard-wired connection. The

challenge is to select the right wireless networking

protocol and implement it in a cost-effective manner.

The Microchip MiWi™ Wireless Networking Protocol

Stack is a simple protocol designed for low data rate,

short distance, low-cost networks. Fundamentally

based on IEEE 802.15.4™ for Wireless Personal Area

Networks (WPANs) later expanded to support

Microchip proprietary RF transceivers, the MiWi

protocol provides an easy-to-use alternative for

wireless communication. In particular, it targets smaller

applications that have relatively small network sizes,

with few hops between. MiWi protocol now is one of the

wireless communication protocols that are supported in

MiWi™ Development Environment (DE). It uses

MiMAC interface to communicate with Microchip RF

transceivers and uses MiApp interface to interact with

application layer.

For more information, please refer to the Microchip

application note AN1283 “Microchip Wireless Media

Access Controller - MiMAC” (DS01283) and AN1284

“Microchip Wireless Application Programming

Interface - MiApp” (DS01284).

This application note covers the definition of the MiWi

Wireless Networking Protocol Stack and how it works.

For completeness, this document also introduces

several aspects of wireless networking, as well as key

features of IEEE 802.15.4. However, it is assumed that

the user is already familiar with the C programming

language and IEEE 802.15.4. You are strongly advised

to read the IEEE 802.15.4 specification and MiMAC/

MiApp application notes in detail prior to using the

Microchip MiWi Wireless Networking Protocol Stack.

FEATURES

The current implementation of the MiWi protocol has

these features:

• Support all Microchip RF transceivers on different

frequency bands.

• Portable between various Microchip MCU

families.

• RTOS and application independent

• Out-of-box support for the MPLAB® C18, C30 and

C32 compilers

• Easy-to-use API

CONSIDERATIONS

A network using the MiWi protocol is capable of having

a maximum of 1024 nodes on a network. Each

coordinator is only capable of having 127 children, with

a maximum of 8 coordinators in a network. Packets can

travel a maximum of 4 hops in the network and 2 hops

maximum from the PAN coordinator.

If, after reading this application note, you determine

that you require a standardized wireless platform,

larger network sizes or common marketing logos,

please refer to the application notes AN1232

“Microchip ZigBee-2006 Residential Stack Protocol”

(DS01232) and AN1255 “Microchip ZigBee PRO

Feature Set Protocol Stack” (DS01255). Alternatively,

users may consider using the basic MiWi protocol and

modifying it to suit their own applications.

For more information on the most up-to-date list of

limitations of the Stack, refer to the Readme file located

with the Stack download at http://www.microchip.com/

miwi.

TERMINOLOGY

In describing the MiWi protocol, two specific terms are

used throughout that are borrowed from the IEEE

standard.

The first term is cluster, which refers to a grouping of

nodes that form a network. A MiWi protocol cluster can

be up to 3 nodes deep and is controlled by a cluster-

head. In the current implementation of the MiWi protocol,

the cluster-head is always the PAN coordinator. (For

more information, see Table 2.)

The second term is socket, also referred as “Indirect

Message” in MiApp interface. It refers to a virtual

connection between two devices. Rather than have an

exclusive hard-wired connection between devices,

many devices with many types of sockets share a

common communications medium and use some

common method to associate applications and

devices. When a new device or application is added to

the network, it requires configuration to communicate

Author: David Flowers and Yifeng Yang

Microchip Technology Inc.

Microchip MiWi™ Wireless Networking Protocol Stack

AN1066

to other devices or applications. By using sockets,

nodes in the network can find communication partners

dynamically without having to know any information

about them.

MiWi PROTOCOL OVERVIEW

The MiWi protocol is based on the MAC and PHY

layers of the IEEE 802.15.4 specification, and is

tailored for simple network development in the 2.4 GHz

and subGHz ISM frequency bands. The protocol

provides the features to find, form and join a network,

as well as discovering nodes on the network and route

to them. It does not cover any application-specific

issues, such as how to select which network to join to,

how to decided when a link is broken or how often

devices should communicate.

IEEE 802.15.4 MAC

The MiWi protocol uses IEEE Standard 802.15.4 as

reference to develop its MAC layer.

Similar to IEEE 802.15.4, MiWi protocol uses an

Acknowledged data transfer mechanism in the MAC.

This method uses a special ACK flag in the packet

header. When this flag is set, Acknowledgement to the

transmitter by its receiver is required; this ensures that a

frame is, in fact, delivered. If the frame is transmitted with

an ACK flag set and the Acknowledgement is not

received within a certain time-out period, the transmitter

will retry the transmission for a fixed number of times

before declaring an error.

It is important to note that the reception of an

Acknowledgement simply indicates that a frame was

properly received by the MAC layer. However, it does not

indicate that the frame was processed correctly. It is

possible that the MAC layer of the receiving node

received and Acknowledged a frame correctly, but due

to the lack of processing resources, a frame might be

discarded by upper layers. As a result, the upper layers

of the application may require additional

Acknowledgement response.

Device Types

IEEE 802.15.4 defines devices based on their overall

functionality. There are basically two device types as

shown in Table 1.

The MiWi protocol defines three types of MiWi protocol

devices, based on their functions in the network: PAN

Coordinator, Coordinator and End Device. The MiWi

Wireless Networking Protocol Stack functionality helps

to determine the type of IEEE functionality that the

device requires. The MiWi protocol device types and

their relationship to IEEE device types are shown in

Table 2.

TABLE 1: IEEE 802.15.4™ FUNCTIONAL DEVICE TYPES

TABLE 2: MiWi™ PROTOCOL DEVICE TYPES

Device Type Services Offered Typical Power Source Typical Receiver Idle

Configuration

Full Function Device (FFD) All or Most Mains On

Reduced Function Device

(RFD)

Limited Battery Off

Device Type IEEE Device Type Typical Function

PAN Coordinator FFD One per network. Forms the network, allocates network

addresses, holds binding table.

Coordinator FFD Optional. Extends the physical range of the network. Allows

more nodes to join the network. May also perform monitoring

and/or control functions.

End Device FFD or RFD Performs monitoring and/or control functions.

AN1066

MiWi PROTOCOL NETWORK

CONFIGURATIONS

Of the three device types defined in the MiWi protocol,

the most essential type to networking is the PAN

coordinator. The PAN coordinator is the device that

starts the network, and selects the channel and the

PAN ID of the network. All other devices joining onto

the PAN have to obey the instructions of the PAN

coordinator.

Star Network Configuration

A star network configuration (Figure 1) consists of one

PAN coordinator node and one or more end devices. In

a star network, all end devices communicate only with

the PAN coordinator. If an end device needs to transfer

data to another end device, it sends its data to the PAN

coordinator, which in turn, forwards the data to the

intended recipient.

Cluster Tree Network Configuration

In a cluster tree network (Figure 2) there is still only one

PAN coordinator; however, other coordinators are

allowed to join on to the network. This forms a tree-like

structure, where the PAN coordinator is the root of the

tree, the coordinators are the branches of the tree and

the end devices are the leaves of the tree. In a cluster

tree network, all of the messages sent through the

network follow the path of the tree structure. Since

messages may be routed through more than one node

to reach their eventual destination, cluster tree networks

are sometimes also referred to as multi-hop networks.

FIGURE 1: STAR NETWORK CONFIGURATION

FIGURE 2: CLUSTER TREE TOPOLOGY

PAN Coordinator

FFD End Device

RFD End Device

Legend

PAN Coordinator

FFD End Device

RFD End Device

Coordinator

Legend

Specyfikacje produktu

Marka:	Microchip
Kategoria:	nieskategoryzowany
Model:	PIC18F86K90

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