Application Note 038
Contents
1. All other trademarks registered trademarks and product names are the sole property of their respective owners 5 4 Life Support Policy Chipcon s products are not designed for use in life support appliances devices or other systems where malfunction can reasonably be expected to result in significant personal injury to the user or as a critical component in any life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system or to affect its safety or effectiveness Chipcon AS customers using or selling these products for use in such applications do so at their own risk and agree to fully indemnify Chipcon AS for any damages resulting from any improper use or sale 2005 Chipcon AS All rights reserved j SWRA055 Page 13 of 14 TEXAS INSTRUMENTS Green Products Application Note 038 from Texas Instruments 6 Address Information Web site http www chipcon com E mail wireless chipcon com Technical Support Email support chipcon com Technical Support Hotline 47 22 95 85 45 Headquarters Chipcon AS Gaustadall en 21 N 0349 Oslo NORWAY Tel 47 22 95 85 44 Fax 47 22 95 85 46 E mail wireless chipcon com US Offices Chipcon Inc Western US Sales Office Chipcon Inc Eastern US Sales Office 19925 Stevens Creek Blvd 35 Pinehurst Avenue Cupertino CA 95014 2358 Nashua New Hampshire 03062 USA USA Tel 1 408 973 7845 Tel 1 62. 172 ms difference with the RX timeout and should constitute sufficient percentual margin for coping with possible oscillator frequency offsets due to temperature and voltage variations With 1 0 ms packet interval the transmitter in the WOR example transmits 305 packets for each wake up burst meaning tpacket burst 305 1 0 ms 305 ms gt tevento 300 ms The extra margin is added because of possible oscillator and timer variations The packet interval decides the TX duty cycle in this case a TX duty cycle of 352 us 1000 us 100 35 2 Another important aspect is that the packet spacing the time from the end of one packet to the start of the next one has to be sufficiently large to account for the necessary time for state transitions between IDLE and TX and also possibly any frequency synthesizer FS calibrations This means that in this example the 6C1100 CC2300 will not have 1000 us 352 us 648 us in IDLE for each packet sent the delays between state transitions have to be subtracted If we for this simple packet burst protocol assume it is only necessary with an initial manual FS calibration before the burst starts and there is no calibration prior to each packet within the burst the IDLE to TX transition will take 88 4 us and the conversely TX to IDLE takes 0 1 us without calibrations This leaves a theoretical time of 559 5 us in IDLE state per packet sent All these time values are assuming a 26 0 MHz crystal An i
3. ees EE y Figure 1 Wake on Radio procedure It is important to notice that the time between an EVENTO and the following EVENT1 cannot be set too short Provided that the XOSC is powered down while the radio is in SLEEP there must be enough time for the XOSC to start after the wake up If automatic calibration of the frequency synthesizer when entering RX is enabled teven must be set long enough to also finish the calibration of the frequency synthesizer before RX starts The tevent timer is configurable through the WORCTRL register In order to ensure that a valid sync word is detected by the WOR receiver when using a packet bursting wake up protocol i e packets are repeatedly sent with a fixed time interval it is important to set the timeout for sync word search in RX properly denoted trx time in figure 1 The timeout must be greater than the interval between transmitted packets If this criterion is not fulfilled the receiver might in worst case end up polling in between sync words missing out on all the packets This subject will be further illustrated in the protocol description of the WOR example An overview of the principal WOR related registers for the 607100 062300 is found in table 1 j SWRA055 Page 4 of 14 TEXAS INSTRUMENTS G ghipcon Products Anplication Note 038 from Texas Instruments Table 1 WOR related registers lIOCFG2 GDO2_CFG 5 0 GDO2 GDO1 and GDOO output pins configuration respectively At
4. it the MCU will check the 607100 2500 s RX FIFO for content and check any packet s validity Meanwhile the receiving unit will be waiting in FSTXON state prepared to rapidly transmit an ACK If there is no need to send an ACK the MCU will issue the SIDLE command strobe to go back to IDLE state and then the SWOR strobe continuing in WOR mode Almost similarly the transmitter will automatically switch to RX instead of IDLE at the end of each packet transmission MCSM1 TXOFF MODE RX This is necessary to listen for any ACKs while at the same time being time saving compared to a manual SRX strobe The receiver is ACKing the packets with a payload byte equal to the inverted command byte received The remote control parses the ACK packet in order to verify that it is an ACK for the current joystick position If it is an ACK that has been received the ongoing packet burst is halted If no ACK is detected an RX timeout will put the transmitter back to IDLE For the WOR ack example it is also implemented an upper limit of packets to send without getting any ACK functioning as a packet burst timeout preventing the transmitter to endlessly transmit without any purpose In theory the transmitter should never have to transmit more than 305 packets in a burst as discussed in section 4 2 2 However when running the application example one will occasionally experience that more than 305 packets are transmitted before an ACK is received There
5. least one GDO signal should be used to provide Wake on lOCFG1 GD01_CFG S 0 Radio interrupts to the MCU IOCFGO GDOO_CFG 5 0 PKTCTRL1 WOR_AUTOSYNC Automatically synchronize the WOR timer to the received packet CC1100 only in Wake on Radio mode If enabled the timer will automatically reset the WOR timer when a sync word is detected The auto sync function is not discussed in this application note MCSM2 RX_TIME 2 0 Timeout for sync word search in RX The timeout is relative to the programmed EVENTO timeout For relation with trx time See below MCSM0 XOSC_FORCE_ON Force the XOSC to stay on in the SLEEP state Normally not set with the intention of minimizing power consumption when in SLEEP but may be used when reduced wake up time is necessary WOREVT1 EVENTO 15 8 High and low byte of the EVENTO timeout register configuring he RX polling i l f la for te low WOREVTO EVENTO 7 0 the polling interval See formula for tevento below WORCTRL RC_PD Powers down the RC oscillator Must be set to 0 to enable the RC oscillator for WOR applications WORCTRL EVENT 1 2 0 EVENT timeout Configures the number of RC oscillator clock periods to wait after EVENTO before EVENT1 should occur see data sheet Time for potential crystal stabilization and or calibration of the frequency synthesizer must be considered if XOSC has been turned off while in SLEEP MCSMO0 XOSC_FORCE_ON or auto calibration is enabled MCSMO FS_AUTOCAL WORCT
6. relatively short time interval setting WOR RES 0 gives a fitting resolution By using equation 1 and assuming a 26 0 MHz crystal used on CCTIOO CCZS00EM EVENTO can be determined 300 ms _ EVENTO 2 EVENTO 10400 2840 3 26 0 MHz This word is split into the two byte sized registers WOREVT1 and WOREVTO which constitute the high and low byte of the EVENTO timeout register i e WOREVT1 28 and WOREVTO A01 The transmitter is configured for operating at a bit rate of 250 kbps which gives a necessary TX time of at least 352 us to send the 88 bit long packet To achieve less than 0 5 RX duty cycle the timeout for the sync word search in RX has to be less than i SWRA055 Page 8 of 14 TEXAS INSTRUMENTS G ghipcon Products Anplication Note 038 from Texas Instruments 300 ms 0 5 100 1 5 ms These two values 352 us and 1 5 ms represents the theoretical absolute minimum and maximum value for trx time Having the WOR RES decided to be 0 equation 3 an appropriate RX timeout within the duty cycle limit may be found by using the given equation 2 12 5 Le time duty cycle RX _TIME 0 lt 0 5 gt RX TIME gt 5 4 Choosing MCSM2 RX TIME 5 1012 corresponds to an RX timeout of 300 ms 2 300 ms 256 1 172 ms 12 59 S Ee 0 391 duty cycle WOR d _ time With a known RX timeout period we are able to determine the TX packet interval A packet interval of 1 0 ms would make a 0
7. the burst will be displayed on the LCD For the WOR example the number of packets in a burst is constant but for the WOR ack example the burst will continue until an ACK has been received or a timeout occurs The blue LED will toggle for each packet sent For the WOR ack example the green LED will toggle every time a valid ACK has been received and the red LED will toggle for non valid packets received If the RX unit is selected it will automatically enter the Wake on Radio mode waiting for packets For the WOR example every time a packet has been detected and the radio is sending an interrupt signal to the MCU the blue LED will toggle For the WOR ack example the blue LED will only be toggled when it is transmitting an ACK For both examples a toggle of the green LED will indicate a packet has been received successfully and the red LED will toggle whenever an invalid packet has been received The LCD will continuously display how many valid packets have been received together with the position of the joystick on the remote control Both programs can be terminated by pressing the S1 button after the setup has been done This will turn off the yellow LED j SWRA055 Page 12 of 14 TEXAS INSTRUMENTS Green Products Application Note 038 from Texas Instruments 5 General Information 5 1 Document History Revision Date LDesertetonichanges 2005 11 22 Initial release 5 2 Disclaimer Chipcon AS bel
8. whenever the radio detects a valid sync word and also take care of what to do next after the radio has been awoken from WOR mode For this protocol example the MCU checks the CRC status of the packet parses the payload and regardless of the result puts the 667100 2300 back to SLEEP as soon as possible continuing the Wake on Radio mode in order to minimize the power consumption 4 2 2 Timing calculations The transmitted packets within a wake up packet burst should be uniformly spaced in time something that can be achieved by using a programmable timer in the MCU to trigger off each packet To reduce the remote control s TX duty cycle and subsequently the power consumption the 667700 CC2300 enters the IDLE state in between each packet Worth noting is that increasing the IDLE period of the transmitter by increasing the packet interval will reduce the TX duty cycle But to still fulfill the need of having an RX polling period at least the size of the packet interval the RX duty cycle has to increase correspondingly increasing the RX duty cycle These considerations have to be adjusted according to specifications of the application As a system specification for this example a limit of 0 5 RX duty cycle has been set at the receiver as maximum while still minimizing the power consumption on the transmitter side to a certain degree Firstly the EVENTO register value corresponding to a 300 ms RX poll interval must be calculated For this
9. 03 888 1326 Fax 1 408 973 7257 Fax 1 603 888 4239 Email USsales chipcon com Email eastUSsales chipcon com Figure 8 Wireless 10509 Vista Sorrento Parkway Suite 420 San Diego CA 92121 USA Tel 1 858 522 8500 ext 6 Fax 1 858 552 8501 Email sales f8w com Sales Office Germany Sales Office Asia Chipcon AS Chipcon AS Riedberghof 3 Unit 503 5 F D 74379 Ingersheim Silvercord Tower 2 30 Canton Road GERMANY Tsimshatsui Hong Kong Tel 49 7142 9156815 Tel 852 3519 6226 Fax 49 7142 9156818 Fax 852 3519 6520 Email Germanysales chipcon com Email Asiasales chipcon com Sales Office Japan Chipcon AS 403 Bureau Shinagawa 4 1 6 Konan Minato Ku Tokyo Zip 108 0075 Tel 81 3 5783 1082 Fax 81 3 5783 1083 Email Japansales chipcon com Chipcon AS is an ISO 9001 2000 certified company 2005 Chipcon AS All rights reserved j SWRA055 Page 14 of 14 TEXAS INSTRUMENTS
10. C Chipcon Products from Texas Instruments CC1100 CC2500 Wake on Radio Keywords e C1100 e 662500 e Wake on Radio 1 Introduction The low cost highly integrated multi channel 6 1100 CC2300 RF transceiver offers Wake on Radio WOR functionality intended for ultra low power wireless applications By using this feature for automated low power RX polling the user obtains an attractive starting point for implementing power saving applications for ultra low power systems This application note outlines code examples taking advantage of the Wake on Radio functionality featured by the CC1100 CC2300 chip which are part of the I TEXAS INSTRUMENTS SWRAO55 Application Note 036 By E Syvertsen S Namtvedt e Ultra low power e Implementation example CC1100 CC1150DK and CC2550DK respectively CC2500 The WOR examples are designed as primitive wireless remote control systems whose intention is to provide an insight into important considerations when using the WOR functionality It is demonstrating a packet bursting transmitter and a Wake on Radio receiver Page 1 of 14 G ghipcon Products Application Note 038 from Texas Instruments Table of Contents KEYWORDS EEN 1 1 INTRODUC TION EE 1 2 LION el EN 2 3 WAKE ON RADIO WOR ccccccceeeeeeeeeeeeeeeeeeeaseeeeeaeeseaseeseas esses eeseasesoaneesoaeesonnessanaes 3 3 1 WOR GbicCpLES 3 3 2 WOR AND CCG1TI00OICGCG 200 3 3 2 1 EE 4 4 WOR EXAM
11. PLES USING CC1100 CC2500 ccc ececeeseeceeeseeeeeesauseuseeeeeseuseuseusauees 6 4 1 GENERAL DESCRIPTION OF ESAMDLES rerna ernan nnne nene 6 4 2 WOR EXAMPLE SIMPLE PACKET BURST PROTOCOL ESAMPDLE T 4 2 1 PYOTOCOl desti DUON esnasinda piinaa 7 4 2 2 RE 8 4 3 WOR ACK EXAMPLE PACKET BURST PROTOCOL WITH AC 10 4 3 1 Protocol deseri pU ON eebe eebe a a i e ARa a aR R 10 4 3 2 EE l1 4 4 RUNNING THE EXAMPLES cccceceececcecceceeceeceeuececeeneeaeceeneceeceeneeaeeeeseeaeeueeeeaeeneenenenaes 12 5 GENERAL INFORMATION ccccececcecceceeceececeueeeseeeeseeeeseususeseuseueeuseeeueeuseuseeeuseneeeees 13 5 1 DOCUMENT FS TY cancer tate sce ec EAE A neta tin este E A 13 5 2 BI e 18 aa EE 13 5 3 TRADEMARK EE 13 5 4 LIFE SUPPORT az EE 13 6 ADDRESS INFORMATION ccccceceececcecseceseeseeceeeuseuseeceeeuseuseeeuseususeueeuseueueeuseuseeeunes 14 2 Abbreviations ACK Acknowledgment packet CRC Cyclic Redundancy Check EB Evaluation Board EM Evaluation Module FS Frequency Synthesizer GDO General Data Output MCU Microcontroller Unit RF Radio Frequency RSSI Received Signal Strength Indicator RX Receive mode SPI Serial Peripheral Interface TX Transmit mode WOR Wake on Radio XOSC Crystal oscillator j SWRAO55 Page 2 of 14 TEXAS INSTRUMENTS G ghipcon Products Anplication Note 038 from Texas Instruments 3 Wake on Radio WOR 3 1 WOR priciples For many battery operated point to point commu
12. RL WOR_RES 1 0 Controls the time resolution of EVENTO and other WOR settings See data sheet for possible resolutions MCSMO0 FS_AUTOCAL 1 0 Configures whether when to perform automatic calibration of the frequency synthesizer between state transitions MCSM1 RXOFF_MODE 1 0 Selects the next state after finishing packet reception MCSM1 TXOFF_MODE 1 0 Selects the next state after finishing packet transmission The relations between timeout values and register values for some of the registers in table 1 are given by the following expressions RX polling interval bg e EVENTO 2508 85 1 Event 0 XOSC Sync word search timeout while in RX TEN GT JO IES b RX TIME lt 7 12 5 2 SRE THEORY duty cycle WOR i SWRA055 Page 5 of 14 TEXAS INSTRUMENTS G ghipcon Products Anplication Note 038 from Texas Instruments For MCSM2 RX TIME 7 1119 the radio will stay in RX until a packet has been received i e no actual timeout Please see the 607100 C 23500 data sheet for descriptions of the other registers 4 WOR examples using CC1100 CC2500 4 1 General description of examples The two WOR examples described in this application note can be considered as implementations of the same simple control system for a radio controlled object The system is modeled as a simplex system with a transmitting remote control sending packets with control commands to the remotely controlled receiving object WOR is used to reduce p
13. TX unit object RX WOR unit Joystick Figure 2 System setup for both examples showing CC2500 In order to achieve a low latency remote control the response time of the system must be sufficiently small For this system an RX polling interval tevento of 300 ms has been set as an i SWRA055 Page 6 of 14 TEXAS INSTRUMENTS G ghipcon Products Anplication Note 038 from Texas Instruments upper bound on the response time when disregarding potential packet errors To avoid unnecessarily long duty cycles both examples operate with a rather small packet format It is possible that the remote control only transmits commands describing the changes at the controls e g the new state of the controller joystick information not requiring more than one byte of data payload per packet Thus the examples will use the 1 byte fixed length packet format shown in figure 3 Preamble Sync word 4 bytes 4 bytes Figure 3 Packet format in WOR example Preamble bytes and sync word will be added automatically by the 661100 CC2300 when transmitting When operating with a fixed payload length in this case one byte there is no need for a length byte The optional one byte address field is also excluded due to simplicity The data byte contains the necessary joystick state information The last two CRC bytes are appended automatically provided that CRC calculations are enabled This means that only the single byte marked with bl
14. ar protocol as the WOR example but this has been extended by including support for acknowledge ACK of each received packet Upon a joystick movement the remote control EB starts bursting identical packets until it gets an ACK back from the receiving EB This means that there in contrast to the previous example is no fixed number of packets in a burst In order for the remote control to be able to detect the acknowledgement packets that will make it halt the packet burst it has to switch to RX for a short period in between each packet In addition the remotely controlled EB still referred to as the receiver since the data traffic still is simplex will now have to transmit an ACK in response of a received packet The ACK is sent immediately after a valid packet has been received If the receiver is awoken from the Wake on Radio mode by receiving an invalid packet wrong packet length containing CRC error etc no reply will be sent The MCU will in either case make the receiver go back to WOR mode Due to protocol changes the WOR EB will be programmed to automatically switch to the FSTXON state when a packet has been received instead of to the default IDLE state MCSM1 RXOFF MODE FSTXON FSTXON is a state where the frequency synthesizer is left on ready to start transmitting The transmission starts very quickly after the STX command strobe has been issued When the WOR EB has received a valid sync word and the MCU has been made aware of
15. are two possible reasons for why this might be happening 1 The receiver was in RX while the packet was transmitted but something disturbed the signal so that the radio was not able to receive the packet properly 2 The receiver did receive the packet and transmitted an ACK but the transmitter did not receive the ACK This again can be due to two different things e Same as 1 above j SWRA055 Page 10 of 14 TEXAS INSTRUMENTS G ghipcon Products Application Note 038 from Texas Instruments e The RX timeout on the transmitter was too short due to the RC Oscillator bug on CC2500 Please refer to CC2500 Errata Note 001 4 3 2 Timing calculations For the WOR ack example some of the timing properties are kept equal to those used for the WOR example At the receiver side the polling period of 300 ms and the RX duty cycle are preserved still with an RX timeout of 1 172 ms Accordingly the transmitter still operates with a packet interval of 1 0 ms The FS calibration routines are also maintained the transmitter only performs a calibration at the start of each packet burst and the receiver performs a calibration prior to every RX polling period Whenever the receiver detects a packet the transition from RX to FSTXON will take 9 6 us The transmitting 007100 6623500 will almost simultaneously execute the 21 5 us lasting transition from TX to RX After a small delay in software RX FIFO must be checked for packet data pro
16. cessing etc the MCU on the receiving EB will have decided whether to send an ACK or not Refer to figure 7 for protocol timing details This delay is expected to clearly exceed the difference in transition time of almost 12 us The RX timeout of the transmitter must therefore be set long enough to still wait in RX when the sync word of a potential ACK is sent To transmit 4 bytes of preamble plus 4 bytes of sync word at 250 kbps takes 256 us Adding certain delay margins for propagation delay and processing time sets the RX timeout at the transmitter to 325 us A sketch of this can be found in figure 6 It would also have been possible to let the RX never time out i e wait in RX for a packet until the 1 0 ms timer triggers off the next packet to be transmitted This would of course have increased the duty cycle of the transmitter tpacket_interval 1000 US Manual frequency synthesizer calibration IDLE Joystick X Ss S g CSS SH SE TS l y N ix N on o gt U R N on o event x T KS T Tt 6 T T T O T F D F D a Ed s D Figure 6 Remote control timing for the packet burst with ACK listening The introduction of ACK to this simple protocol causes an increase of duty cycle on both sides In addition to the 35 2 TX duty cycle the transmitter will experience an RX duty cycle of 325 us 1 0 ms 100 32 5 The price of ACKing is not as high for the receiver as for the transmitter the 6C1100 CC2500 wit
17. h WOR will only have an extra TX duty cycle of 352 us 300 ms 100 0 117 at maximum together with the already 0 391 RX duty cycle j SWRA055 Page 11 of 14 TEXAS INSTRUMENTS G Green Products Application Note 038 from Texas Instruments tevento 300 ms Se II Ww CH O N Detected pkt m lt OD 2 Il GA or 3 N el gt lt NOXLS4 XOSC start up IDLE SLEEP FS calibration Event Event Event Event ert 9 6 sr ZGE sr 10 N OD Figure 7 Receiver timing for the Wake on Radio with ACK reply 4 4 Running the examples For a description of how to load the programs into your SmartRF 04EB please refer to the publication CC1100 CC2500 Examples Libraries User Manual found on the Chipcon website http Mwww chipcon com Together with the hex files the source code with comments will be found Before running the programs EB units must be configured to either be the transmitter unit bursting packets or the receiver unit using Wake on Radio This is done in the setup menu by moving the joystick sideways move it left to choose TX unit and right for RX WOR unit Push the S1 button to confirm your choice After the unit has been configured the yellow LED will turn on If the TX unit is selected you are now able to push the joystick button or move it up down left or right This will start the packet burst and the number of packets sent in
18. ieves the information contained herein is correct and accurate at the time of this printing However Chipcon AS reserves the right to make changes to this document without notice Chipcon AS does not assume any responsibility for the use of the described product neither does it convey any license under its patent rights or the rights of others The latest updates are available at the Chipcon website or by contacting Chipcon directly As far as possible major changes of product specifications and functionality will be stated in product specific Errata Notes published at the Chipcon website Customers are encouraged to sign up to the Chipcon Newsletter for the most recent updates on products and support tools When a product is discontinued this will be done according to Chipcon s procedure for obsolete products as described in Chipcon s Quality Manual This includes informing about last time buy options The Quality Manual can be downloaded from Chipcon s website Compliance with regulations is dependent on complete system performance It is the customer s responsibility to ensure that the system complies with regulations 5 3 Trademarks SmartRF is a registered trademark of Chipcon AS SmartRF is Chipcon s RF technology platform with RF library cells modules and design expertise Based on SmartRF technology Chipcon develops standard component RF circuits as well as full custom ASICs based on customer requirements and this technology
19. llustration of the packet burst timing is shown in figure 5 tpacket_interval 1000 US Manual frequency synthesizer calibration IDLE V GA GA Joystick Ny Sp w oOo a Qo w Oo o t SS Wu S event A N E P N Z 7 T o T T T n S I T Vu T Vu T n SA Figure 5 Timing for the simple packet burst example showing start of burst On the Wake on Radio side the receiver is recommended to enable automatic calibration of the frequency synthesizer whenever switching from IDLE to RX Configuring the MCSMO FS AUTOCAL register bits equal to 012 does this In most cases including this example the XOSC_ FORCE ON bit of the MCSMo register is left unset turning off the XOSC i SWRA055 Page 9 of 14 TEXAS INSTRUMENTS G ghipcon Products Anplication Note 038 from Texas Instruments when entering SLEEP state during WOR mode to reduce the power consumption When the radio wakes up to IDLE state at EVENTO there must be enough time for the crystal to start up and stabilize typically 300 wus and for the calibration of the frequency synthesizer typically 809 us before the RX can begin at EVENT 1 in total a wait period of over 1 1 ms This implies the WORCTRL EVENT1 bits for this case must be set equal to 1112 configuring teventi 1 38 ms with a 26 0 MHz crystal 4 3 WOR ack example packet burst protocol with ACK 4 3 1 Protocol description The WOR ack example is using a simil
20. nication systems without the need of constant throughput but with strict demands of power efficiency the simple configuration with an always on receiver and an infrequently transmitting station will in most cases not fulfill the desired power budget By using the principle of receive mode RX polling the reduction of the RX duty cycle obtained makes low power applications feasible especially in asymmetric systems where all units do not have equal requirements for low power consumption In addition to minimize the power consumption it is a good idea to put the radio in a power saving sleep state in between the RX polling periods by disabling all functionality that is not necessary at that time The advantage with WOR is that the RX polling is fully automated by the radio and there is no need for the microcontroller MCU to interfere strobe RX commands This means that also the MCU can stay in power down mode and further save power while waiting for a packet The MCU will only have to wake up when the radio actually detects a packet it only has to Wake on Radio activity This is the reason WOR is a useful feature for power saving applications 3 2 WOR and CC1100 CC2500 The Wake on Radio functionality of 6C1100 CC2300 enables it to stay in a power saving SLEEP state and periodically wake up from deep sleep and listen for incoming packets in RX without microcontroller interaction The programmable wake up period is controlled by a WOR
21. or transmitted packets every 300 ms to obtain a suitably low response time Upon any change of state of the remote control s joystick the transmitter initiates a burst by sending a fixed number of identical packets To make sure the receiver has a chance to acquire one of the packets the burst durability cannot be less than the time spacing between two subsequent RX periods tpacket burst gt tevento This will ensure that at least one RX poll period will occur during the wake up burst period It is also important that the receiver s RX period lasts at least as long as the entire packet interval tex time gt tracket interval to ensure that at least one incoming sync word will coincide with the receiver s RX poll period If this is not fulfilled the receiver might risk start listening right after a sync word has been transmitted and stop listening right before the subsequent sync word is sent and as a consequence miss out on the whole burst of packets Please note that if the receiver is detecting a sync word right before the RX is timing out it will stay in RX until the end of the packet potentially extending the duty cycle like illustrated with the last RX poll in figure 4 By looking at figure 4 it may seem like the receiver goes back to the SLEEP state automatically after receiving a packet This is not correct When a packet has been received the radio switches to the IDLE state The MCU should have been programmed to receive an interrupt
22. ower consumption at the receiver side Since both examples are implementations of the same remote control system they are very similar but they are using different protocols The first and most primitive example is implemented as a purely simplex system with no transmission error control The transmitter is set to burst a fixed number of packets relying on one of them being detected by the WOR receiver The second example can be considered as an improvement of the first one because of its expansion to also include ACKs from the receiver to verify each received packet Even if 667100 2300 is a multi channel RF transceiver both examples utilize only a single channel Please note that the examples are not supposed to be an ideal complete example implementation of a remote control system Their main purpose is to serve merely as a demonstration of how to use the WOR functionality of 607100 C 2300 Because of this some aspects are left out for better illustrating WOR The example code is written for two SMartRF 04EB Evaluation Boards using the on board Silicon Labs C8051F320 MCU together with GCTI00 CC2500EM One evaluation board EB is configured to be the remote control TX unit and the other as the remotely controlled object RX WOR unit The joystick position on the remote control is displayed on the LCD of the remotely controlled EB A system setup is modeled in figure 2 CEZ300 CE2500 Remote Remotely control controlled
23. timer run by an internal RC oscillator This implies that the RC oscillator must be enabled before the WOR strobe command can be used The radio s configurable GDO pins are used to signal the interrupts intended for the MCU on the desired event For instance if a sync word is detected during the RX period the 6C1100 CC2300 can trigger an interrupt to wake up the MCU The MCU can then make a decision on what to do next e g switch to TX and send an ACK or if the CRC of the received packet failed continue in WOR mode go back to SLEEP In the latter case after a packet has been received the radio will always go to the IDLE state That means that if it is desirable to continue in WOR mode the MCU manually has to strobe another WOR command on the SPI If no sync word is detected while in RX a programmable RX timeout will make the chip automatically return to sleep mode and continue in WOR mode without interrupting the MCU The Wake on Radio functionality may also be used in combination with 6C1100 CC2300 e RX_TIME_RSSI function This function will perform an initial RSSI level measurement when entering RX mode and if the RSSI value does not exceed a programmable threshold the RX will terminate immediately and return to SLEEP still in WOR mode This function can reduce the time in RX and contribute to lower power consumption if no signal is present The 667700 offers two different methods of using WOR with or without the automatic s
24. ue is fetched from the TX FIFO buffer and the rest is generated by the radio itself For more details and possibilities regarding the packet format see the CCTI00 CE2500 data sheets 4 2 WOR example Simple packet burst protocol example 4 2 1 Protocol description The WOR example uses a simplex protocol scheme illustrated in figure A This simple protocol does not provide any form for ACK confirming a received packet and packet traffic is therefore solely uni directional Because of its simplicity and despite its unreliability the protocol is a fitting example illustrating the main concepts of using WOR Remote control TX unit teacket_interval lt trx time tpacket_burst gt tevento TX TX VC 4 ee wu Lu Ste IDLE Och IDLE i f La 2 2 Joystick i Joystick EER t event S event SL S Bee sal ae Controlled object RX WOR unit RX RX Potential RX Potential E RX ti t i RX timeout a Imeou SLEEP SLEEP SLEEP Ev Ev1 Ev Ev1 tevento 300 ms Evo Ev1 t tex time 1 17 ms ee e Figure 4 Example protocol without ACK j SWRA055 Page 7 of 14 TEXAS INSTRUMENTS G ghipcon Products Anplication Note 038 from Texas Instruments In this example the receiver is configured to wake up and perform an RX poll searching f
25. ynchronization feature while 662300 offers only WOR without autosync This application note will only look at WOR applications not using autosync i SWRA055 Page 3 of 14 TEXAS INSTRUMENTS G ghipcon Products Anplication Note 038 from Texas Instruments 3 2 1 WOR without auto sync The simplest way to utilize WOR is when a transmitter continuously bursts packets at a fixed interval In this case by configuring the receiver to wake up regularly to listen for a packet it is not necessary to use the autosync feature The frequency of the low power RC oscillator controlling the WOR timer varies with temperature and voltage supply To keep this frequency as accurate as possible the RC oscillator is calibrated when the crystal oscillator XOSC is running and the radio is not in the SLEEP state The clock used by the WOR timer is then a divided XOSC clock When the radio enters the SLEEP state the RC oscillator will use the last valid calibration result The time when 667100 2500 wakes up from the SLEEP state and the time when the radio is starting RX mode are denoted as EVENTO and EVENT respectively The course of events is shown in figure 1 The wake up interval shown as tevento in figure 1 Le the time between two consecutive EVENTOs and also two consecutive EVENTS is configured with the WOREVT registers tex time tex time 7 f RX SLEEP ERX SLEEP EVENTO EVENT1 EVENTO EVENT1 Jemp t EE d t Evento PE ee ee
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