Overview of ZigBee

1
Overview of ZigBee Serial Communication Using
RS232C

• Sunggu Lee, Gil Won Hong
• Pohang Univ. of Science and Technology
• July 21, 2006

2
The 802 Wireless Space
WWAN
IEEE 802.22
IEEE 802.20
WMAN
WiMax IEEE 802.16
Range
WLAN
WiFi 802.11
ZigBee 802.15.4
802.15.3 802.15.3a 802.15.3c
Bluetooth 802.15.1
WPAN
0.01
0.1
1
10
100
1000
Data Rate (Mbps)
ZigBee network Topologies(adapted from 3)
3
802.15.4 Application Space

• Sensors Controls
• Home Automation
• Industrial Automation
• Remote Metering
• Automotive Networks
• Interactive Toys
• Active RFID/ asset tracking
• Medical

4
General Characteristics

• Dual PHY (2.4GHz and 868/915MHz)
• Data rates of 250 kbps (_at_2.4GHz), 40 kbps
  (_at_915MHz), and 20 kbps(_at_868MHz)
• CSMA-CA channel access
• Carrier Sense Multiple Access with Collision
  Avoidance (CSMA-CA)
• Multiple topologies
• Range 50m typical (5-500m based on environment)
• Refer to http//www.zigbee.org

5
ZigBee Physical Device Type

• To allow vendors to supply the lowest possible
  cost devices, the IEEE standard defines 2 types
  of devices
• Full function device (FFD)
• Can function in any topology
• Capable of being network coordinator
• Can talk to any other device (FFD/RFD)
• Generally line powered
• Reduced function device (RFD)
• Limited to star topology
• Cannot become network coordinator
• Talks only to network coordinator (FFD)
• Simple implementation min RAM and ROM
• Generally battered powered

6
ZigBee Network Topologies
Mesh
Star
PAN coordinator
Full Function Device
Cluster Tree
Reduced Function Device
ZigBee network Topologies(adapted from 2)
7
ZigBee Channel Access Options

• Two channel access mechanisms
• Non-beacon network
• A simple, traditional multiple access system used
  in simple peer and near-peer networks
• Standard CSMA-CA communications
• Positive acknowledgement for successfully
  received packets
• Beacon-enabled network
• Superframe structure- network coordinator
  transmits beacons at predetermined intervals
• Dedicated bandwidth and low latency
• Low Power Consumption mode for Coordinator

8
Synchronization

• PAN coordinator transmits beacon frames
  periodically to announce the superframe structure
• A device needs to know the superframe structure
  before any data transmission can begin

9
Superframe Patrick 2003

• The format of the superframe is defined by the
  coordinator
• The superframe is bounded by network beacons, is
  sent by the coordinator and is divided 16 equally
  sized slots
• Any device wishing to communicate during the
  contention access period between two beacons
  shall compete with other devices using a slotted
  CSMA-CA mechanism

Superframe(adapted from 1)
10
Guaranteed Time Slots Patrick 2003

• For low latency applications or applications
  requiring specific data bandwidth, the PAN
  coordinator may dedicate portions of the active
  superframe to that application

Guaranteed time slots(adapted from 1)
11
RS232C Serial Interface

• Serial Communication
• Synchronous
• A clock signal is sent with the data to
  indicate the presence of valid data (data valid
  on upward transition of clock)
• Asynchronous
• No separate clock signal is required
• Requires handshaking to send and receive data
  properly
• With no predetermined data rate
• Handshakes are required for every data item sent
• With a predetermined data rate
• Handshakes need to be sent after every K bits of
  data
• The value of K is determined by how closely the
  receiver and transmitter clocks are synchronized

12
Protocol Overview

• Commonly supported data rates
• 115,200, ,19,200, 9,600, 4,800, and 2,400 bits
  per second (bps)
• Typically uses a DB-25 or DB-9 connector
• Main signals
• Rx signal used to receive data
• Tx signal used to send data
• CTS clear-to-send handshaking signal
• RTS request-to-send handshaking signal
• Signal ground
• Serial data word example (Fig. 5.2 of Hordeski
  1995 1 start bit, 8 data bits, 1 or 2 stop bits

Sampling Points
Stop Bit
Idle
Start Bit
Data (8 bits)
13
References

• 1 Patrick Kinney, ZigBee Technology wireless
  control that simply works, White Paper, Oct.
  2003.
• 2 William C. Craig , Zigbee Wireless Control
  That Simply Works, White Paper.
• 3 J. A Gutierrez ,IEEE 802.15.4 A Developing
  Standard for Low-Power Low-Cost Wireless Personal
  Area Networks, IEEE Networks, Sep./Oct. 2001.
• 4 Hordeski, Michael, Personal Computer
  Interfaces, McGraw-Hill Companies, 1995.
• 5 IEEE Standard 802.15.4, http//www.ieee.org.
• 6 http//www.zigbee.org