Application Report
SLAA365–July2007
Clear Channel Asssment
Using TI MSP430and CC2500Radio Randy Wu Technical Staff
ABSTRACT
This application report describes a2.4-GHz anti-jamming frequency-hopping system
consisting of a designated Transmitter and Receiver,each with distinct functions to
avoid RF-channel interference.The Transmitter board emulates the control device
(e.g.,remote control)by nding commands to be procesd on the Receiver side
(e.g.,TV,stereo,t top box,or gaming console).Since many popular consumer
devices u the 2.4-GHz RF ,cordless phones,wireless routers,
microwaves,and PC/Bluetooth®accessories),the systems need to implement a
proprietary frequency-hopping scheme in the event that the channel being ud by the
Transmitter/Receiver pair is already being ud by other wireless systems in the
vicinity.The specific radio device ud for this demo is the TI CC2500(2.4GHz)RF
transceiver module.The TI portfolio also includes the CC1100RF transceiver
(315/433/868/915-MHz ISM/SRD bands),which shares a common t of configuration
registers as tho ud in the CC2500.This makes it easy to switch between the two
RF transceiver devices,so the radio-specific portion of this demo can be ud for both
types of TI CCxxxx devices.
Contents
1Introduction (2)
2Hardware Evaluation Platform (2)
中国传统文化手抄报3Application Function and Usage (4)
4Theory of Operation (6)
5Software Architecture (10)
6Conclusion (12)
7References (12)
Appendix A MSP430+CCxxxxEMK Demo Board Configuration (13)
Appendix B Software Flow Charts (14)
List of Figures
1MSP430FG4618Experimenter Board (2)
2LCD Display Icons (5)
出入拼音3Receiver Function Flow Chart (6)
4Transmitter Function Flow Chart (7)
5Repeated Data Packets Write Burst Timing (8)
6ACK Reception During Burst Write Sequence (9)
All trademarks are the property of their respective owners.
1Introduction
2
Hardware Evaluation Platform 2.1Texas Instruments MSP430FG4618Experimenter
Board
Introduction
The system described in this application report implements a channel-hopping scheme in which the
Receiver continuously scans a predetermined t of RF channels for clarity and jumps to the clearest
channel,while the Transmitter continuously cycles through the RF channels until it receives an
acknowledgement from the Receiver to maintain a continuous wireless RF link.This implementation of
"link maintenance"allows both the Transmitter and Receiver to be continuously in sync with each other
会议安排
and ready to transmit data in both directions,waiting for an event (e.g.,ur button press)on the
Transmitter side while the Receiver needs to be on the clearest channel to ensure that messages nt
back and forth have the highest probability of success of reaching their final destinations.
The low cost and ultralow-power MSP430plus CCxxxx-bad RF demo described in this application
report leverages existing development boards manufactured by Texas Instruments.With this
implementation,the MSP430remains in Low Power Mode 3(LPM3)most of the time where the chip itlf consumes an average of only 0.8μA!The CCxxxx on the Transmitter side features a Wake-On-Radio
(WOR)feature,whereby the device periodically goes to sleep and wakes up to catch potential incoming packets.This conrves power by reducing the time it stays in a fully active Receiver mode,since tting any active transmit or receive mode for any RF transceiver device consumes more power vs.an idle mode state.In most cas,the average current consumption (for the radio itlf)configured for WOR mode is approximately 100μA!
For ea of development,the SmartRF™Studio graphical ur interface tool suite can be downloaded
and ud to automatically generate CCxxxx configuration register ttings bad on any combination of desired operation configurations.
The MSP430FG4618/F2013Experimenter Board is a comprehensive development target board that
can be ud for a number of applications.Wireless communication is possible through an expansion header which is compatible with all TI wireless evaluation modules.In addition,interfaces to a 4-mux LCD,UART connection,microphone,audio output jack,buzzer,and capacitive touch pad enable the development of a variety of applications.Communication between the two onboard MSP430devices is also possible.All
pins of the MSP430FG4618device are made available either via
for easy
debugging.Basic sample code for this board is available online at Figure 1.MSP430FG4618Experimenter Board
Clear Channel Asssment Using TI MSP430and CC2500Radio 2SLAA365–July 2007内蒙古小肥羊餐饮连锁有限公司
2.2TI CCxxxxEMK Daughterboard
2.3Benefits of Using the TI CCxxxx RF Transceiver Hardware Evaluation Platform
Interface to the wireless world is accomplished via the wireless evaluation module header supporting the CCxxxxEMK boards from TI.The transceiver modules are connected to the USART of the
MSP430FG4618configured in
Software libraries that interface the MSP430to
the transceivers are available at The demo application implemented in this application report relies on the as the foundation for the low-level interactions between the MSP430and CCxxxx devices.
The CCxxxx is a low cost,true single-chip RF transceiver designed for very low power wireless applications.The circuit is intended for the ISM(Industrial,Security,and Medical)and SRD(Short Range Device)frequency bands.The RF transceiver is integrated with a highly configurable baband modem. The modem supports various modulation formats and has a configurable data rate of up to500kbps.The CCxxxx provides extensive hardware support for effective RF communications,such as packet handling, data buffering,burst transmissions,clear channel asssment,link quality indication,and WOR.The main operating parameters and the64-byte transmit and receive buffer FIFOs can be controlled via standard
3-wire SPI interface.Only a few passive components are required to interface the CCxxxx with the
MSP430ultralow-power microcontroller.By using the TI CCxxxx device,the following features greatly benefit the system with respect to RF communications:
•Automated packet handling–automates training,frame synchronization,addressing,and error detection
•Wake-On-Radio(WOR)–achieves automatic low-power periodic Receiver polling
•Tx-If-CCA™feature(CCA)–prevents multiple Transmitter collisions and automatically arbitrates the data direction for listen-before-talk systems
•Forward error correction(FEC)with interleaving–reduces gross bit error rate when operating near the nsitivity limit
•Carrier n(CS)–enables detection of busy channels ud by other potentially interfering systems
(e.g.,wireless router,cordless phone)
•Link quality indicator(LQI)–estimates how easily a received signal can be demodulated;can be ud as a relative measurement of the link quality
•Automatic frequency compensation(AFC)–align own frequency to the received center frequency •Manchester encoding–provides an additional level of data integrity for packet transmissions
•Deep64-byte Tx FIFO data buffer–allows MCU to store sufficient amounts of data pending to be transmitted by the CCxxxx at any time,regardless of what the CCxxxx is doing
•Deep64-byte Rx FIFO data buffer–allows CCxxxx to store sufficient amounts of received data and save it for the MCU to be read at any time
•Efficient standard SPI interface–all registers can be programmed with one"burst"transfer
•Digital RSSI output–allows the MCU to quickly read(in real-time)a simple8-bit byte reprenting the Received Signal Strength Indicator of the last received data packet
3
Application Function and Usage 3.1Receiver Board
3.2Transmitter Board
工会选举选票模板Application Function and Usage
When the Receiver board is first powered up,it parks itlf on frequency #1(denoted as F1on the LCD display).Pressing SW2once increments the RF channel to the next frequency until the last (highest
numbered channel)pret frequency has been reached.The next button press enables the Receiver
board's AUTO scan mode (AUTO is displayed on the LCD just below the RF channel markers).Once the Receiver is in this AUTO mode,it periodically scans all of the RF channel prets and jump to the clearest channel if communications with the Transmitter board has been lost.Pressing the SW2button while the Receiver board is in AUTO scan mode ts the board's frequency back to F1,and AUTO scan mode is
disabled until the subquent SW2button press,once the board is t on the highest-numbered pret
RF channel.
When the Receiver board is parked (due to manual channel change or auto scan mode)on a pret RF channel,the Antenna icon on the LCD display stays on,and when the Receiver board is scanning through a round of the pret channels,the Antenna icon is cleared during this brief amount of time.During the
channel scan quence,in the event that the Receiver happens to receive a broadcast beacon from t
he Transmitter,an acknowledge is not nt back until the channel scan has been completed.This way,the Receiver does not mistakenly nd back an acknowledge while the Transmitter beacon that is nt out
during a normal scan period coincides with the Receiver's channel scan quence.
Whenever the Receiver board receives a valid packet and determines that the packet contains its own
hard-coded address,the Mailbox/Envelope icon on the LCD display flashes momentarily (approximately one cond).
Pressing SW1on the Receiver board nds a command to toggle LED1on the Transmitter board.Since the Transmitter board is most likely configured for WOR mode,the delay between the pressing of SW1
and the toggling of LED1is more noticeable to the human eye.
When the Transmitter board is first powered up,it parks itlf on frequency #1(denoted as F1on the LCD display).Pressing SW1and SW2once nds a command to toggle LED1or LED2on the Receive
r board,respectively.
When the Transmitter board is parked on one of the pret RF channels,the Antenna icon on the LCD
display stays on,and whenever the Transmitter board is scanning each RF channel looking for the河南最好的高中
Receiver board,the Antenna icon is cleared during this time.The Transmitter board periodically nds out a broadcast beacon to the Receiver.If the Receiver nds back an acknowledge to the beacon request,the Transmitter board remains on its currently-lected pret RF channel.If no respon to the beacon is received,the Transmitter cycles through each pret RF channel until it receives an acknowledge to the beacon request,and at that time the Transmitter parks itlf on the currently-lected channel.
Whenever the Transmitter board receives a valid packet and determines that the packet contains its own hard-coded address,the Mailbox /Envelope icon on the LCD display flashes momentarily (approximately one cond).
Clear Channel Asssment Using TI MSP430and CC2500Radio 4SLAA365–July 2007
3.3
Ur Interfaces 3.3.1LCD
Display
3.3.2LED Functions
Application Function and Usage期货交易市场
The LCD display on each board is ud as an interface for ur functions and feedback:
•Tx or Rx –denotes Transmitter or Receiver configuration (determined at project build time)
•Antenna –denotes the board is currently ttled on an RF channel;disappears whenever Receiver is scanning channels in AUTO mode and whenever Transmitter is cycling through channels looking for
the Receiver
•Mailbox/Envelope –blinks for approximately (at most)one cond whenever a valid packet (with a packet ID which matches the hard-coded address of the board receiving the message)has been
decoded
•AUTO –displayed in the lower right-hand corner whenever channel-hopping auto scan mode is enabled via SW2(applies to Receiver mode configurations only)
•F1F2F3F4F5–shows which pret RF channel the board is currently parked on;highest channel number depends on the amount of pret channel frequencies programmed in the application software
(only one of the channel prets can be lected at any one time)
Figure 2.LCD Display Icons
The LEDs are also ud to provide feedback on the interactions between the demo boards:
•LED1–mapped to the other board's Switch #1(SW1)for LED1Toggle commands
•LED2–mapped to the other board's Switch #2(SW2)for LED2Toggle commands
•LED4–turns on whenever a transmit burst quence is initiated;turns off whenever the corresponding acknowledge has been received (ud to determine ACK turnaround time)
偶尔怀念
4
Theory of Operation 4.1Receiver Operation
Theory of Operation
The main responsibilities of the Receiver consist of the following:
•Scan all preprogrammed RF channels at periodic intervals
•Detect RF carrier on each channel during scan mode and maintain incrementing "carrier n busy counters"for each channel
•Asss which channel is the clearest and jump to that channel if communications with the Transmitter have been lost
•Decode incoming packets from the Transmitter,process the command as quickly as possible,and then generate an acknowledge packet to nd back to the Transmitter to verify reception of the command
packet
In this system,the Receiver acts as the "RF Master"in regards to determining which RF channel is to be ud at any time.It has the responsibility of clearest channel asssment and determines which channel to park on to avoid other RF sources that may be jamming the currently-lected RF channel.Once the Receiver has parked,it assumes the Transmitter will find the Receiver during times of nonactivity on a
periodic basis.
Figure 3.Receiver Function Flow Chart
Clear Channel Asssment Using TI MSP430and CC2500Radio 6SLAA365–July 2007
