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© 2010 Microchip Technology Inc. DS01066B-page 1
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
DS01066B-page 2 © 2010 Microchip Technology Inc.
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.
© 2010 Microchip Technology Inc. DS01066B-page 3
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

Product specificaties

Merk: Microchip
Categorie: Niet gecategoriseerd
Model: PIC18F47J13

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