AC4790 User`s Guide - Laird Technologies
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1. Hong Kong 852 2923 0610 www lairdtech com ramp AC4790 User s Manual Version 2 0 Write Destination Address The OEM host issues this command to the transceiver to change the destination address Note Only the three least significant bytes of the MAC address are used for packet delivery Command OxCC 0x10 MAC3 MAC2 MAC1 Number of Bytes Returned 4 Response OxCC MAC3 MAC2 MAC1 Parameter Range 0x00 OxFF corresponding to 3 LSB s of destination MAC Address Read Destination Address The OEM host issues this command to the transceiver to read the destination address Note Only the three Least Significant Bytes of the MAC Address are used for packet delivery Command OxCC 0x11 Number of Bytes Returned 4 Response OxCC MAC3 MAC2 MAC1 Parameter Range 0x00 OxFF corresponding to 3 LSB s of destination MAC Address Auto Destination The Host issues this command to change the Auto Destination setting When issuing this command the Auto Destination setting will only be changed if the corresponding enable bit is set Control1 Parameter EEPROM address 0x56 bit 4 Command OxCC 0x15 Data Number of Bytes Returned 2 Response OxCC Data2 Parameter Range Datal bit 0 Auto Destination bit 4 Enable Auto Destination modification Data2 bit 0 New Auto Destination setting bits 2 7 O Read API Control The OEM host issues this command to read the API Control b2. Figure 3 AC4790 Configuration Flow AT Commands The AT Command mode implemented in the AC4790 creates a virtual version of the Command Data pin The Enter AT Command mode command asserts this virtual pin Low to signify Command mode and the Exit AT Command mode command asserts this virtual pin High to signify Data mode Once this pin has been asserted Low all on the fly CC commands documented in the manual are supported On the Fly Control Commands The AC4790 transceiver contains static memory that holds many of the parameters that control the transceiver operation Using the CC command set allows many of these parameters to be changed during system operation Because the commands write to static memory these parameters will revert back to the settings stored in the EEPROM when the transceiver is reset While in CC Command mode using pin 17 Americas 1 800 492 2320 Option 2 9 Laird Technologies Europe 44 1628 858 940 Hong Kong 852 2923 0610 www lairdtech com ramp AC4790 User s Manual Version 2 0 Command Data the RF interface of the transceiver is still active Therefore it can receive packets from remote transceivers while in CC Command mode and forward these to the OEM host While in CC Command mode using AT commands the RF interface of the transceiver is active but packets sent from other transceivers will not be received The transceiver uses Interface Timeout RF Packet Size to determine when a CC c
3. acknowledgment Case 2 In this case a radio loads its Session Count with its Session Count Refresh its Transmit Retries This case is suitable for applications where there are high levels of interference and it is likely that transmit retries will be necessary to maintain reliable communications When an addressed packet or a response to a broadcast packet is sent the sending radio will listen for a successful acknowledgement If an acknowledgement is not sent the radio will resend the packet until either an acknowledgement is received or it has exhausted all available transmit retries If two radios are on the last hop of the current session and a retry is required it is possible that once the current session has ended the receiving radio could go into session with a different radio and miss the final packet of the previous session Adding the radios Transmit retries to its Current Session Count will ensure that the radio does not exit the session when the remote radio is using a Transmit Retry Case 3 In this case a radio loads its Session Count with the remote radio s Session Count Refresh This is suitable for full duplex applications as the Session is extended as long as there is communication Note This is the default case with which the radio ships and may not work well for all applications Use Case 4 when a large number of data packets are lost during operation Americas 1 800 492 2320 Option 2 6 Laird Technologies Eu
4. between 1 and 2 1 and 4 1 and 8 1 and 16 1 and 32 1 and 64 1 and 128 and 1 and 256 In a very dense network where many transceivers could experience a collision it is important to have a higher random backoff seed Tip What effects will Random Backoff have on system latency As the random backoff value increases the overall system latency increases Worst case latency Half Duplex 50ms Number of retries Max random value Worst case latency Full Duplex 100ms Number of retries Max random value Americas 1 800 492 2320 Option 2 19 Laird Technologies Europe 44 1628 858 940 Hong Kong 852 2923 0610 www lairdtech com ramp AC4790 User s Manual Version 2 0 NETWORKING System ID System ID EEPROM address 0x76 is similar to a password character or network number and makes network eavesdropping more difficult A transceiver will not establish a session or communicate with a transceiver operating on a different System ID or Channel Number RF Channel Number Channels 0x00 OxOF and 0x30 0x37 hop on 26 different frequencies Channels 0x10 Ox2F use 50 different frequencies Table 5 RF Channel Number Settings 0 AC4790 1x1 0x00 OxOF 902 928 MHz 26 hop bins US Canada AC4790 200 1 AC4790 1x1 0x10 Ox2F 902 928 MHz 50 hop bins US Canada AC4790 1000 2 AC4790 1x1 0x30 0x37 915 928 MHz 22 hop bins US Canada 1x1 200 AC4790 200 Australia 1x1 200 1000 AC4790
5. for the 900 MHz ISM band AC4790 transceivers operate in a masterless architecture When an AC4790 has data to transmit it enters transmit mode and starts transmitting a sync pulse intended for an individual radio or broadcasts to all transceivers within the same network and range Intended receivers synchronize to this sync pulse a session begins and data is transmitted This instinctive dynamic peer to peer networking architecture enables several transceiver pairs to carry on simultaneous conversations on the same network To boost data integrity and security the AC4790 uses Laird s FHSS technology featuring optional Data Encryption Standards DES Fully transparent these transceivers operate seamlessly in serial cable replacement applications Communications include both system and configuration data via an asynchronous TTL serial interface for OEM host communications Configuration data is stored in an on board EEPROM and most parameters can be changed on the fly All frequency hopping synchronization and RF system data transmission reception is performed by the transceiver transparent to the OEM host This document contains information about the software interface and configuration of a Laird AC4790 transceiver Refer to the AC4790 Hardware Integration Guide for hardware interface information The OEM is responsible for ensuring the final product meets all appropriate regulatory agency requirements listed herein before selling any produ
6. much latency will be introduced in the system when considering high density applications In these cases we can only offer qualitative analysis of the latency in high density applications As the network load increases then the number of collisions that will occur increases As the number of collisions increase then the system latency increases As the distance between the transceivers increases so does the system latency Finally when transceivers operate in addressed mode they will retry sending a packet up to the number of time specified in the transmit retry parameter specified in the EEPROM As the number of retries increases the system latency will also increase System Throughput When operating as shown in Table 4 an AC4790 can achieve the listed throughput However in the presence of interference or at longer ranges the transceiver may be unable to meet the specified throughput Table 4 Maximum System Throughput Radio not in continuous session 25 kbps 12 5 kbps Radio continuously in session 45 kbps 22 5 kbps Random Backoff The AC4790 uses Carrier Sense Multiple Access CSMA protocol with random backoff and a selectable backoff seed In a packet collision the AC4790 backs off and retries the packet When two transceivers detect a collision each chooses a random number of packet times that it waits before retrying This number is selected from a pool of numbers defined by the backoff seed and consists of a number
7. who does have the key and the algorithm can easily decrypt the encrypted data and obtain the original data Thus a standard algorithm based on a secure key provides a basis for exchanging encrypted data by only issuing the encryption key to authorized recipients Americas 1 800 492 2320 Option 2 22 Laird Technologies Europe 44 1628 858 940 Hong Kong 852 2923 0610 www lairdtech com ramp AC4790 User s Manual Version 2 0 EEPROM PARAMETERS The OEM host can program various parameters that are stored in EEPROM which become active after a power on reset Table 6 gives the locations and descriptions of the parameters that can be read written by the OEM host Factory default values are also shown Do not write to any EEPROM addresses other than those listed in Table 6 Do not copy one transceiver s EEPROM to another transceiver as doing so may cause the transceiver to malfunction Table 6 EEPROM Parameters Product ID 0x00 40 40 bytes Product identifier string Includes revision information for software hardware Stop Bit Delay 0x3F 1 0x00 OxFF For systems employing RS485 interface or OxFF Parity the stop bit might come too early Stop bit delay controls the width of the last bit before the stop bit occurs OxFF Disable Stop Bit Delay 12 us 0x00 256 1 6 us 12 us 0x01 OxFE value 1 6 us 12 us Channel Number 0x40 1 Ox00 1x1 0x00 Set 0 0x00 DOE US Canada 1x1 200 0x37 200 0x00 Set 1 0x10 0x2
8. 0x02 0x04 Specifies a byte gap timeout used in Timeout OxFF conjunction with RF Packet Size to determine when a packet coming over the interface is complete 0 5ms per increment RF Packet Size 0x5B 1 0x01 0x80 Used in conjunction with Interface Timeout 0x80 specifies the maximum size of an RF packet CTS On Ox5C 1 Ox01 OxD2 CTS will be deasserted High when the OXFF transmit buffer contains at least this many characters CTS Off 0x5D 1 0x00 OxAC Once CTS has been deasserted CTS will be OxFE reasserted Low when the transmit buffer is contains this many or fewer characters Max Power 0x63 1 0x00 Setin Used to increase decrease the output 0x60 Production power The transceivers are shipped at amp can vary maximum allowable power Parity Ox6F 1 OxE3 Ott OxE3 Enable Parity OXFF OxFF Disable Parity Note Enabling parity cuts throughput and the interface buffer size in half Destination ID 0x70 6 0x00 Specifies destination for RF packets OxFF System ID 0x76 1 0x00 0x01 Similar to network password Radios must OxFF share a system ID to talk with each other RS485 DE Ox7F 1 OxE3 Datt OxE3 GOO is active Low DE for control of OxFF external RS485 hardware OxFF Disable RS485 DE MAC ID 0x80 6 0x00 Factory programmed unique IEEE MAC OxFF address Original Max Ox8E 1 Set in Copy of original max power EEPROM Power production setting This address may be referenced but may vary should not be modified Americas 1 800 492 2
9. 1000 1 All channels in a Channel Set use the same frequencies in a different order DES Data Encryption Standard DES encryption is the process of encoding an information bit stream to secure the data content The DES algorithm is a common simple and well established encryption routine An encryption key of 56 bits is used to encrypt the packet The receiver must use the exact same key to decrypt the packet otherwise the data will be garbled To enable DES EEPROM Byte 0x45 bit 6 must be set to a value of 1 To disable DES set bit 6 to a value of O The 7 byte 56 bits Encryption Decryption Key is located in EEPROM Bytes OxDO OxD6 It is highly recommended that this Key be changed from the default Max Power Max Power allows control of the RF output power of the AC4790 Output power and current consumption can vary by as much as 10 per transceiver for a particular Max Power setting Contact Laird for assistance in adjusting Max Power Note The max power is set during production and may vary slightly from one transceiver to another The max power can be set as low as desired but should not be set higher than the original factory setting A backup of the original power setting is stored in EEPROM address Ox8E Americas 1 800 492 2320 Option 2 20 Laird Technologies Europe 44 1628 858 940 Hong Kong 852 2923 0610 www lairdtech com ramp AC4790 User s Manual Version 2 0 SECURITY The 4790 product family u
10. 2 transceivers 2 development boards 2 7 5V DC unregulated power supplies 2 serial cables 2 USB cables 2 antennas configuration testing software and integration engineering support Americas 1 800 492 2320 Option 2 26 Laird Technologies Europe 44 1628 858 940 Hong Kong 852 2923 0610 www lairdtech com ramp AC4790 User s Manual Version 2 0 APPENDIX l API NETWORK TOPOLOGIES API The API feature set of the AC4790 provides powerful packet routing capabilities to the OEM host The number of API configurations is endless as individual radios can all be configured differently to suit the OEM host s varying needs Some of the most common implementations are described in the following pages Polling Network Many applications require multiple locations to report back to a single access point One solution is to enter Command mode change the transceiver s destination address and then exit Command mode to resume normal operation When it is time to communicate with another transceiver the process is repeated costing time and inevitably reduction in throughput as unnecessary commands are issued As an alternative the Transmit API command can be used to control packet routing on a packet by packet basis 1 2 A FARN MAC 12 34 A3 5 4 MAC 12 34 A4 MAC 12 34 56 Shared Access Point MAC 12 34 A5 MAC 1234 A6 Channel 0x10 System ID 0x01 Figure 5 A sample polling network The simplest implementation cons
11. 2 86 60 25 81 82 58 1A 80 7D 56 16 79 79 54 13 78 75 52 11 77 72 50 OE 76 6F 48 OD 75 6B 46 OC 74 68 44 OB 73 66 42 to 39 OC 72 63 36 to 22 OB Note The RSSI becomes saturated at levels above 40 dBm and does not follow the curve Read ADC The OEM host issues this command to read any of the three onboard 10 bit A D converters Because the RF is still active in on the fly Command mode the transceiver will not process the command until there is no activity on the network The Read RSSI command is therefore useful for detecting interfering sources but will not report the RSSI from a remote transceiver on the network The equations for converting these 10 bits into analog values are as follows Analog Voltage 10 bits Ox3FF s 3 3V Temperature C Analog Voltage 0 3 0 01 30 RSSI value dBm 105 0 22 0x3FF 10 bits Command OxCC 0x21 Data Number of Bytes Returned 3 Response OxCC Data2 Data3 Parameter Range Datal 0x00 AD In 0x01 Temperature 0x02 RSSI Data2 MSB of requested 10 bit ADC value Data3 LSB of requested 10 bit ADC value Write Digital Outputs The OEM host issues this command to write both digital output lines to particular states Note This command should only be used when Protocol Status OxC2 is not set to OxE3 Command OxCC 0x23 Data Number of Bytes Returned 2 Response OxCC Data1 Parameter Range Da
12. 320 Option 2 24 Laird Technologies Europe 44 1628 858 940 Hong Kong 852 2923 0610 www lairdtech com ramp AC4790 User s Manual Version 2 0 Product ID 0x90 15 0x90 0x93 Product ID 0x94 0x95 Prefix CL or AC 0x96 0x99 Power 200M 200A 1000 1x1 Note There will be a period in front of the 1x1 to keep the field at four bytes Ox9A Ox9C Interface 232 485 TTL Ox9D Ox9E Setup script 01 is stock Ox9F Reserved for future use always OxFF API Control OxC 1 1 0x10 Settings are bit 7 Broadcast packets 0 Addressed Packets 1 Broadcast Packets bit 6 Probe 0 Disable Probe 1 Enable Probe bit 5 Stock 0 Disable 1 Enable bit 4 SLockO 0 Disable 1 Enable bit 3 Unicast Packets 0 Broadcast or Addressed delivery 1 Addressed packets only bit 2 Send Data Complete Enable 0 Disable 1 Enable bit 1 API Transmit Packet Enable 0 Disable 1 Enable bit O API Receive Packet Enable 0 Disable 1 Enable Protocol Status OxC2 1 Ox00 OxE3 Determines if the GOO amp GO1 server as OxFF generic output or as protocol status Session Count OxC4 1 0x00 0x08 Specifies the number of hops a transceiver Refresh OxFF stays in session with another transceiver Random Back OxC3 1 0x00 0x00 The random amount of time a transceiver Off OxFF waits when a collision occurs before resending the packet again 0x00 Disable Random Backoff 0x01 Wait 1 2 packet times then retry 0x03 Wait 1 4
13. Byte 4 of Byte5 Byte 6 Address Dest MAC Auto Destination OxCC 0x15 bit 0 Auto Destination OxCC bit 0 Auto Destination bit 4 Enable Auto Destination bits 1 7 O Read API Control OxCC 0x16 OxCC API Control Write API Control OxCC 0x17 API Control OxCC API Control Read Digital Inputs OxCC 0x20 OxCC bit 0 GIO bit 1 GI1 Read ADC OxCC 0x21 0x01 AD In OxCC MSB of 10 LSB of 10 bit 0x02 Temp bit ADC ADC 0x03 RSSI Write Digital OxCC 0x23 bit 0 GOO OxCC bit 0 GOO Outputs bit 1 GO1 bit 1 GO1 Set Max Power OxCC 0x25 New Max Power OxCC Max Power Enter Probe OxCC Ox8E 0x00 Enter Probe OxCC 0x00 or 0x01 Exit Probe 0x01 Read Temp OxCC OxA4 OxCC Temp C EEPROM Byte Read OxCC OxCO Start Address Length OxCC Starting Length Data Address EEPROM Byte Write OxCC OxC1 Start Address Length Data Starting Address Length Data written Soft Reset OxCC OxFF Americas 1 800 492 2320 Option 2 10 Laird Technologies Europe 44 1628 858 940 Hong Kong 852 2923 0610 www lairdtech com ramp AC4790 User s Manual Version 2 0 Command Descriptions Enter AT Command Mode Prior to sending this command the OEM host must ensure that the transceiver s RF transmit buffer is empty If the buffer is not empty the radio will interpret the command as data and it will be sent over the RF This can be accomplished by waiting up to one second between the last packet and the AT command
14. Command 0x41 0x54 0x2B 0x2B 0x2B Ox0D Number of Bytes Returned 4 Response OxCC 0x43 Ox4F 0x4D Exit AT Command Mode The OEM host should send this command to exit AT Command mode and resume normal operation Command OxCC 0x41 0x54 Ox4F Ox0D Number of Bytes Returned 4 Response OxCC 0x44 0x41 0x54 Firmware Version Request The OEM host issues this command to request the firmware of the transceiver Command OxCC 0x00 0x00 Number of Bytes Returned 3 Response OxCC Version XX Parameter Range XX 0x00 0x03 Ignore Change Channel The OEM host issues this command to change the channel of the transceiver Command OxCC 0x01 Channel Number of Bytes Returned 2 Response OxCC Channel Broadcast Packets The OEM host issues this command to change the transceiver operation between Addressed Packets and Broadcast Packets If Addressed Packets are selected the transceiver will send all packets to the transceiver designated by the Destination Address programmed in the transceiver If Broadcast Packets are selected the transceiver will send its packets to all transceivers on that network Setting bit 7 of API Control to 1 can also enable Broadcast Packets Command OxCC 0x08 Data Number of Bytes Returned 2 Response OxCC Data Parameter Range Data 0x00 for Addressed 0x01 for Broadcast Americas 1 800 492 2320 Option 2 11 Laird Technologies Europe 44 1628 858 940
15. Data received in buffer over Host UART Command Yes Data Mode No Type of RF Broadcast Packet Transmit Packet p Decrement Broadcast Attempts Yes No Broadcast Attempts 0 No Figure 2 Pending Serial data in buffer flow Americas 1 800 492 2320 Option 2 8 Europe 44 1628 858 940 Hong Kong 852 2923 0610 www lairdtech com ramp Addressed Packet Transmit Packet Yes Receive ACK Decrement Transmit Attempts Transmit Attempts 0 Laird Technologies AC4790 User s Manual Version 2 0 AC4790 CONFIGURATION The AC4790 can be configured using the CC Configuration commands The CC commands can be issued using either Hardware or Software Configuration To use Hardware Configuration Pin 17 of a transceiver must be asserted Low Software Configuration can be used by entering AT Command Mode before issuing the CC commands The flowchart in Figure 3 illustrates the configuration process Receive Mode J d Yes ye Use AT Ss N Commands SS S AT Take Pin 17 Low Hardware Configuration Software Configuration X Ba SS we D Send CC N p lt Exit Command 2 Commands GC Mode ee Yes D ee In AT Se See je lt Command gt N Mode lt e y Yes e AS Zog GER Send Exit AT e Yes CH adresse gt Command Mode Take Pin 17 High y Z Command SS Receive Mode
16. F US Canada 1x1 1000 1000 0x10 Set 2 0x30 0x37 US Canada 1x1 200 Australia 1x1 200 1000 Baud Rate Low 0x42 1 0x00 OxFC Low byte of the interface baud rate Default OxFF baud rate is 57600 bps Baud Rate High 0x43 1 0x00 0x00 High byte of interface baud Always 0x00 Control 0 0x45 1 0x00 Settings are bit 7 0 bit 6 DES Enable 0 Disable 1 Enable bits 5 0 0 Transmit Retries 0x4C 1 0x01 0x10 Maximum number of times a packet is sent OxFF out when Addressed packets are selected Broadcast Wie 1 0x01 0x04 Maximum number of times a packet is sent Attempts OxFF out when Broadcast packets are selected Stale Count Ox4F 1 0x01 0x40 Determines the amount of time that a Reload OxFF transceiver will keep a radio active in its Receive Table This value is reset every time a packet is received from that radio Americas 1 800 492 2320 Option 2 23 Laird Technologies Europe 44 1628 858 940 Hong Kong 852 2923 0610 www lairdtech com ramp AC4790 User s Manual Version 2 0 Control 1 0x56 1 0x43 Settings are bit 7 Laird Use Only bit 6 Laird Use Only bit 5 Laird Use Only bit 4 Auto Destination 0 Use destination address 1 Use auto destination bit 3 Laird Use Only bit 2 RTS Enable 0 Ignore RTS 1 Transceiver obeys RTS bit 1 Duplex 0 Half Duplex 1 Full Duplex bit 0 Auto Config 0 Use EEPROM values 1 Auto Configure values Interface 0x58 1
17. G EES acavay eiaa aE EN How Spread Spectrum Work 21 Frequency Hopping Spread Spectrum ccccccccececeececeeeeceeececeeeeeeeeceeeeeceeecceeeceeeeneeeeneeecieeestreeseeee 21 AC4790 Security Features 22 EEPROM Parameters 2 eteegege dee TEE eiaa idee Seen ele eed deeg Se 23 Ordering Information 26 Product Part Nummfer Treg NEEN REESEN EES EE EES 26 Developer Kit Part Number cccccceceecceceececeeeseeeeseaeeeceaeeeceeeecaeeeeeeeeseaeeesaeesceeeceeeeseeeesnaeeecceeeeeeeeeeeeees 26 Appendix I API Network Topologies c cceecceceeeceeeeeeeaeeeneeeeeaeeeeaae seas saeeeeaaeseeaaeseaeeseaeeseaeeeeaaeseeaeeenaes 27 EE 27 P lli BCEE 27 EE 28 Time Division Multiple Access Network 31 Related Documents and Files ua 32 Americas 1 800 492 2320 Option 2 3 Laird Technologies Europe 44 1628 858 940 Hong Kong 852 2923 0610 www lairdtech com ramp AC4790 User s Manual Version 2 0 AC4790 TRANSCEIVER The compact AC4790 900MHz transceiver replaces miles of cable in harsh industrial environments Using field proven FHSS technology which needs no additional FCC licensing in the Americas OEMs can easily make existing systems wireless with little or no RF expertise Overview The AC4790 is a member of Laird s RAMP OEM transceiver family The AC4790 is a cost effective high performance frequency hopping spread spectrum FHSS transceiver designed for integration into OEM systems operating under FCC part 15 247 regulations
18. Laird gt AC4790 User s Guide Version 2 0 global local Americas 1 800 492 2320 Option 2 Europe 44 1628 858 940 Hong Kong 852 2923 0610 www lairdtech com ramp AC4790 User s Manual Version 2 0 REVISION HISTORY 1 0 Initial Release 1 1 Changes and Revisions Separated Hardware Integration Guide HIG from User Guide 2 0 19 Dec 2013 information created two separate documents Add Related Documents section Americas 1 800 492 2320 Option 2 2 Laird Technologies Europe 44 1628 858 940 Hong Kong 852 2923 0610 www lairdtech com ramp AC4790 User s Manual Version 2 0 CONTENTS Revision Historie 2 AC4790 Tiranscelve EE 4 O TAY EAV ee eet eege ees eher A CAVE CS ated AAE EA ays asaietaand semrex anda seu sncmeta aginst ae e a A E T a E 4 Theory ge Ce EE 5 Masterless ArchitectUre eeneg dese 5 Megdes OF OPS rath sai e ces estate vac cen as elei 5 AC4790 Configuration tnst An MANE AS ANEAN EEEE EASES NANNAN SEE EASEAEASEES NENEA EEEE NEEE nnne 9 AC OMMNA Se ee Eeer 9 le Me euer egent E EE 9 COMMaNd REI EE 11 API e Ce EE 16 Radio Interface 17 lee 18 Half Duplex Full DUPIEX gissen nets SES 18 System TIMING amp Latency cece cee ee ecee cece ceeeeeeeeeeeeeaeeeeaee ea aeeeeaeeeeaae ea aaesaaeeeeaaeeeaaesdeaaesaeeeeeaeeseaaeseaaesseaeeenaees 19 Systemi lte le 19 Random ET e EE 19 NECWOMKING E 20 MaX Ne EE 20 S GUIILY A Rene ees ed E 21 Spread Spectrum HIStONy xii sesisisseyesncncsa sedans EENE
19. Option 2 29 Laird Technologies Europe 44 1628 858 940 Hong Kong 852 2923 0610 www lairdtech com ramp AC4790 User s Manual Version 2 0 81 06 08 04 12 34 A2 66 69 GE 64 20 64 Payload Data HIND D Destination MAC Address Number of Transmit Retries Session Count Refresh Payload Data Length 3 Radio C receives the packet FIND D and stores it in the buffer until the current session with Radio B has ended Once the current session ends Radio C forwards the packet from its buffer to Radio D 81 06 08 04 12 34 A3 66 69 GE 64 20 64 Payload Data FIND D Destination MAC Address Number of Transmit Retries Session Count Refresh Payload Data Length 4 Radio D receives the packet FIND D and sends the appropriate response back down the line to Radio A Loopback Repeater The simplest repeater to implement is a loopback repeater A loopback repeater can be created by connecting the transceiver s RXD and TXD lines together When the radio receives data it will retransmit the data to all available transceivers on the network It is important not to have two loopback repeaters in range of each other as they will continuously transmit data back and forth MAC 12 34 56 MAC 12 34 A1 MAC 12 34 A2 MAC 12 34 A3 Loopback Repeater Figure 7 Loopback Repeater If radios B amp C in the above picture are not within range of radio A they will not be able to receive or respond to communications from radio A A loopback r
20. and SLock1 settings control Session Count as shown below Table 1 Session Count Truth Table 1 0 0 Radio loads its Current Session Count Radio loads its Current Session Count with its Session Count Refresh with its Session Count Refresh 2 0 1 Radio loads its Current Session Count Radio loads its Current Session Count with its Transmit Retries its Session with its broadcast attempts its Count Refresh Session Count Refresh 3 1 0 Radio loads its Current Session Count Radio loads its Current Session Count with the remote radio s Session Count with the remote radio s Session Count Refresh Refresh 4 1 1 Radio loads its Current Session Count Radio loads its Current Session Count with the remote radio s Current Session with the remote radio s Current Session Count Count EEPROM Default This may not be the best setting for all applications If having issues use Case 4 Note 1 For Broadcast Addressed packets the Session Count for Full Duplex is 2x the value of Session Count in Half Duplex Note 2 It is best to have all transceivers with the same Session Count Refresh EEPROM Address 0xC4 value Session Count Refresh must not be set to 0x00 Case 1 In this case a radio loads its Session Count with its Session Count Refresh This is suitable for Half Duplex communication where immediate response is not expected from the remote radio Note The term immediate response refers to the application layer and not the RF
21. art from the data itself on separate wires Tip Can implement a design using just Txd Rxd and Gnd Three wire Interface Yes However it is strongly recommended that your hardware monitor the CTS pin of the radio CTS is taken High by the radio when its interface buffer is getting full Your hardware should stop sending at this point to avoid a buffer overrun and subsequent loss of data You can perform a successful design without monitoring CTS However you need to take into account the amount of latency the radio adds to the system any additional latency caused by Transmit Retries or Broadcast Attempts how often you send data non delivery network timeouts and interface data rate Polled type networks where the Server host requests data from the client host and the client host responds are good candidates for avoiding the use of CTS This is because no one transceiver can monopolize the RF link Asynchronous type networks where any radio can send to another radio at any point in time are much more difficult to implement without the use of CTS Half Duplex Full Duplex When Half Duplex communication is chosen the AC4790 sends a packet over the RF whenever it can This can cause packets sent by multiple transceivers at the same time to collide with each other over the RF To prevent this Full Duplex communication can be chosen Full Duplex shares the bandwidth intelligently to enable two way collision free communicatio
22. ayload Data STATUS Broadcast Packet Number of Transmit Retries Session Count Refresh Payload Data Length The remote response is dependent on the OEM s specific needs and equipment In many cases remote radios are connected to dumb devices without the intelligence to filter out or append specific portions of a packet that is transmitted or received Since the 7 bytes of overhead in the Transmit API command are not sent over the RF the remotes will receive only the payload data STATUS If auto destination is enabled on the remote radio the transceiver will automatically change its destination address to that of the radio it last received a packet from When the remote device sends its response it will therefore automatically be routed back to the SAP Depending on the API configuration of the SAP the packet will be received in one of two formats Receive API When Receive API is enabled the transceiver will receive the reply data the MAC address of the source radio and two RSSI values RSSI is how strong the remote transceiver heard the local transceiver and RSSI is how strong the local heard the remote transceiver 81 07 XX XX 12 34 A1 61 6C 6C 67 6F 6F 64 Payload Data ALLGOOD Source MAC Address RSSI RSSI Payload Data Length Americas 1 800 492 2320 Option 2 28 Laird Technologies Europe 44 1628 858 940 Hong Kong 852 2923 0610 www lairdtech com ramp AC4790 User s Manual Version 2 0 It may be useful t
23. ct Note Unless mentioned specifically by name the AC4790 modules are referred to as the radio or transceiver Individual naming is used to differentiate product specific features The host any device to which the AC4790 is connected such as a PC are referred to as OFM host Features Networking and Security Easy to Use Masterless True peer to peer point to multipoint Continuous 76 8 kbps RF stream rate point to point Software selectable interface baud rates from Retries and acknowledgements 1200 bps to 115 2 kbps API commands to control packet routing and Low cost low power and small size ideal for acknowledgement on a packet by packet basis high volume portable and battery powered FHSS for security and interference rejection applications Customizable RF Channel number and system ID All modules are qualified for Industrial Hardware Protocol Status monitoring temperatures 40 C to 80 C Two generic input and output digital lines and Advanced configuration available using AT integrated ADC functions commands Americas 1 800 492 2320 Option 2 4 Laird Technologies Europe 44 1628 858 940 Hong Kong 852 2923 0610 www lairdtech com ramp AC4790 User s Manual Version 2 0 THEORY OF OPERATION Masterless Architecture The masterless architecture is a true peer to peer architecture where any module that has data to transmit will initiate a communication session with a transceiver s wit
24. ed the Send Data Complete is received before the transceiver sees the Receive API packet This order may get reversed when the API Send Data Complete is missed and is resent after the API Receive Packet is received Americas 1 800 492 2320 Option 2 16 Laird Technologies Europe 44 1628 858 940 Hong Kong 852 2923 0610 www lairdtech com ramp AC4790 User s Manual Version 2 0 API Transmit Packet API Transmit Packet is a powerful command that allows the OEM host to send data to a single or multiple broadcast transceivers on a packet by packet basis This can be useful for many applications including polling and or mesh networks Refer to the API section for further details API Transmit Packet is enabled when bit 1 of the API Control byte is enabled The OEM host should use the following format to transmit a packet over the RF 0x81 Payload Data Length Session Count Transmit Retries Destination Payload Data 0x01 0x80 Refresh Broadcast Attempts MAC 2 1 0 1 If the OEM host does not encode the header correctly the transceiver will send the entire string up to 0x80 bytes and will look for the header in the next data 2 Although the 7 bytes of overhead are not sent over the RF they are kept in the buffer until the packet is sent Keep this in mind so as not to overrun the 256 byte buffer 3 Setting the MAC to OxFF OxFF OxFF will broadcast the packet to all available transceivers API Send Data Complete API Send Da
25. epeater can be added between the three such that it is in range of both radio A and radios B amp C When the repeater receives a packet from radio A it will transmit the packet out to radios B amp C If the repeater is set to Broadcast mode radio A will receive a copy Americas 1 800 492 2320 Option 2 30 Laird Technologies Europe 44 1628 858 940 Hong Kong 852 2923 0610 www lairdtech com ramp AC4790 User s Manual Version 2 0 of each packet that it sends If the repeater has a specific destination address i e 12 34 A2 then radio A will not receive the packet as its MAC address will not match the specified destination address Time Division Multiple Access Network For a more intelligent network a TDMA system can be implemented In this system various radios transmit data to a Shared Access Point SAP during an assigned time interval The system is synchronous so that only one radio is transmitting at a time and has full access to the SAP s bandwidth In a TDMA network each radio must store its data for the amount of time between its transmissions or bursts A typical format for data passing through a SAP is shown in Error Reference source not found A frame consists of arriving bursts from remote radios and each frame is then divided into multiple time slots The bursts can be of varying lengths and can be longer for heavy traffic stations To prevent overlaps guard intervals can be inserted to absorb small timing errors in bu
26. hat resides on the transceiver The Radio Table stores information for up to the last 8 transceivers that it received a packet from This information can be useful for determining alternative data paths Stale Count The Stale Count Reload 0x04 determines the amount of time that a transceiver stays active in the Radio Table The Stale Count min 0x00 max dependent on EEPROM setting for a radio is set to 0 when a packet is received and then incremented by one every 100ms thereafter When the Stale Count of a transceiver reaches the Stale Count Reload 0x04 the transceiver is considered stale A Radio Table can hold information for up to 8 different transceivers however if the table is full and a ninth radio appears the first stale radio is replaced with the new radio H none of the radios are stale the oldest radio is replaced by the new radio Command OxCC 0x18 Number of Bytes Returned Varies Response OxCC Transceivers MAC2 MAC1 MACO RSSI RSSI StaleCount MAC2 MAC1 MACO etc Table 3 Received Signal Strength 92 CO 71 5F 91 BC 70 5B 90 BB 69 58 89 B9 68 54 88 B8 67 4F 87 AE 66 4B 86 A9 65 47 85 A2 64 43 Americas 1 800 492 2320 Option 2 13 Laird Technologies Europe 44 1628 858 940 Hong Kong 852 2923 0610 www lairdtech com ramp AC4790 User s Manual Version 2 0 RSSI dBm HexValue RSSI dBm Hex Value 84 92 63 3D 83 8D 62 2A 8
27. hin its range network transmit data and exit the session This architecture eliminates the need for a master which dictates network area and synchronizes radios in the network to allow peer to peer communication Modes of Operation The AC4790 has three different operating modes Transmit mode Receive mode Command mode If the transceiver is not communicating with another radio it will be in Receive mode actively listening for a sync pulse from another transceiver If the radio hears a pulse and determines that it is a broadcast or addressed sync pulse it will resoond by going into session with the sending radio A transceiver will enter Transmit or Command mode when the OEM host sends data over the serial interface The state of the Command Data pin Pin 17 or the data contents determine which of the two modes will be entered Transmit Mode All packets sent over the RF are either Addressed or Broadcast packets Broadcast and Addressed delivery can be controlled dynamically with the API Control byte and corresponding on the fly commands Unicast Only can be enabled to prevent transceivers from receiving broadcast packets When a radio has data to transmit it sends out a sync pulse to initiate a session with one or more radios This 25 ms sync pulse is sent during the first half of each 50 ms hop and transparent to the OEM host Once a session has been established the radio transmits the data during the remaining 25 ms of the current h
28. ists of a smart Shared Access Point SAP with a microcontroller or processor of some type which has Transmit API enabled The SAP controls which transceiver s each packet is routed Broadcast packets should be used when all remotes are to receive the same message and addressed packets when communication with a single remote only is desired An example of each is shown in the following pages Addressed Transmit API 1 To poll radio 1 the SAP transmits the packet using the following format 81 06 08 04 12 34 A1 73 74 61 74 75 73 Payload Data STATUS Destination MAC Address Number of Transmit Retries Session Count Refresh Payload Data Length Americas 1 800 492 2320 Option 2 27 Laird Technologies Europe 44 1628 858 940 Hong Kong 852 2923 0610 www lairdtech com ramp AC4790 User s Manual Version 2 0 2 To poll radio 2 the SAP transmits the packet using the following format 81 06 08 04 12 34 A2 73 74 61 74 75 73 Payload Data STATUS Destination MAC Address Number of Transmit Retries Session Count Refresh Payload Data Length 3 This continues until all radios have successfully been polled by the SAP Broadcast Transmit API To send out a universal poll request or data packet the OEM may wish to utilize the broadcast portion of the Transmit API command The Broadcast command is similar to the addressed command only with the Destination MAC Address set to all OxFF 81 06 08 04 FF FF FF 73 74 61 74 75 73 P
29. n The transceiver calculates the amount of time until the next hop determines if there is time to send the packet and sends the packet if possible If not the transceiver waits until its next appropriate hop The radio which initiates the session transmits during the even numbered hops while the remaining radio s will transmit during the odd numbered hops Although the RF hardware is still technically Half Duplex sharing the bandwidth makes the transceiver seem Full Duplex Enabling Full Duplex mode can cause overall throughputs to be cut in half Americas 1 800 492 2320 Option 2 18 Laird Technologies Europe 44 1628 858 940 Hong Kong 852 2923 0610 www lairdtech com ramp AC4790 User s Manual Version 2 0 SYSTEM TIMING amp LATENCY Take care when selecting transceiver architecture as it can have serious effects on data rates latency and overall system throughput The importance of these three characteristics will vary from system to system and should be a strong consideration when designing the system Tip n High density applications what amount of latency should be expected It is not easy to predict the exact amount of latency in high density applications There are many variables that affect system latency The three variables that most affect the latency are the network load the distance between transceivers and whether the transceivers are operating in a broadcast or addressed mode There is no fixed answer as to how
30. ned None Response None API Control API Control is a powerful feature that the masterless protocol offers When enabled the API Transmit Packet API Send Data Complete and API Receive Packet features provide dynamic packet routing and packet accounting ability to the OEM host thereby eliminating the need for extensive programming on the OEM host side These abilities make the masterless protocol ideal for any legacy system API operation utilizes specific packet formats specifying various vital parameters used to control radio settings and packet routing on a packet by packet basis The API features can be used in any combination that suits the OEM s specific needs API Receive Packet By default the source MAC is not included in the received data string sent to the OEM host For applications where multiple radios are sending data it may be necessary to determine the origin of a specific data packet When API Receive Packet is enabled all packets received by a transceiver include the MAC address of the source radio as well as an RSSI indicator which helps determine the link quality between the transceivers API Receive Packet is enabled when bit 0 of the API Control byte is enabled Upon receiving a packet the radio sends its OEM host the packet in the following format 0x81 Payload Data Length 0x01 0x80 RSSI RSSI Source MAC 2 1 0 Payload Data Note When both API Send Data Complete and API Receive Packet are enabl
31. ng Kong 852 2923 0610 www lairdtech com ramp AC4790 User s Manual Version 2 0 Laird Laird Technologies is the world leader in the design and manufacture of customized performance critical products for wireless and other advanced electronics applications Laird Technologies partners with its customers to find solutions for applications in various industries such as Network Equipment s Telecommunications Data Communications Automotive Electronics Computers Aerospace Military Medical Equipment Consumer Electronics Laird Technologies offers its customers unique product solutions dedication to research and development as well as a seamless network of manufacturing and customer support facilities across the globe CONN GUIDE AC4790 v2_0 Copyright 2013 Laird Technologies Inc All rights reserved The information contained in this manual and the accompanying software programs are copyrighted and all rights are reserved by Laird Technologies Inc Laird Technologies Inc reserves the right to make periodic modifications of this product without obligation to notify any person or entity of such revision Copying duplicating selling or otherwise distributing any part of this product or accompanying documentation software without the prior consent of an authorized representative of Laird Technologies Inc is strictly prohibited All brands and product names in this publication are registered trademarks or tradema
32. nnel Numbers System ID is similar to a password character or network number and makes network eavesdropping more difficult A receiving radio will not go in range of or communicate with another radio on a different System ID There are a total of 256 System ID values If FHSS technology Channel Number and System ID are still not enough to secure your data the AC4790 supports the Data Encryption Standard DES which is the third level of security Encryption is the process of encoding an information bit stream to secure the data content The algorithm described in this standard specifies both encrypting and decrypting operations which are based on a binary number called a key A key of 56 bits is used to encrypt and decrypt the data The encryption algorithm specified in this standard is commonly known among those using the standard The unique key chosen for use in a particular application makes the results of encrypting data using the algorithm unique Selection of a different key causes the encrypted data that is produced for any given set of inputs to be different The cryptographic security of the data depends on the security provided for the key used to encrypt and decrypt the data Data can be recovered from the encrypted data only by using exactly the same key used to encrypt it Unauthorized recipients of the encrypted data who know the algorithm but do not have the correct key cannot derive the original data algorithmically However anyone
33. o the OEM host to determine which radio each packet originated from When Receive API is enabled every packet received by the transceiver will be received in the above format Normal Receive Mode non API If Receive API is not enabled the transceiver will receive the reply data only i e ALLGOOD from each transceiver 61 6C 6C 67 6F 6F 64 Received Dala AU 600D Daisy Chain Repeater Network For applications spanning long distances and cases where the desired radio is not within range of the sending radio a daisy chain type network can be implemented With the use of API commands a processor and external buffer a daisy chain or repeater can easily be implemented to store and forward the data to the desired radio Error Reference source not found assumes that radio A has a packet which needs to be received by radio D far right Ia 2 3 MAC 12 34 56 MAC 12 34 A1 MAC 12 34 A2 MAC 12 34 A3 Figure 6 Daisy Chain Repeater Network 1 Radio A transmits the string FIND D to Radio B using the Transmit API command 81 06 08 04 12 34 A1 66 69 GE 64 20 64 Payload Data HIND D Destination MAC Address Number of Transmit Retries Session Count Refresh Payload Data Length 2 Radio B receives the packet FIND D and stores it in the buffer until the current session with Radio A has ended Once the current session ends Radio B forwards the packet from its buffer to Radio C Americas 1 800 492 2320
34. ommand is complete Therefore there should be no delay between each character as it is sent from the OEM host to the transceiver or the transceiver will not recognize the command If the OEM host has sent a CC command to the transceiver and an RF packet is received by the transceiver the transceiver will send the CC command response to the OEM host before sending the packet However if an RF packet is received before the Interface Timeout expires on a CC command the transceiver will send the packet to the OEM host before sending the CC command response When an invalid command is sent the radio scans the command to see if it has a valid command followed by bytes not associated with the command If so the radio discards the invalid bytes and accepts the command Otherwise the radio returns the first byte of the invalid command back to the user and discards the rest Table 2 Command Quick Reference Enter AT 0x41 0x54 0x2B 0x2B 0x2B Ox0D OxCC 0x43 0x4F 0x4D Command mode Exit AT Command OxCC 0x41 0x54 Ox4F 0x0D OxCC 0x44 0x41 0x54 mode Status Request OxCC 0x00 0x00 OxCC Firmware 0x00 Version 0x03 Change Channel OxCC 0x01 New Channel OxCC New Channel Broadcast OxCC 0x08 0x00 Broadcast OxCC 0x00 or Packets 0x01 Addressed 0x01 Write Destination OxCC 0x10 Byte 4 of Byte5 Byte6 OxCC Byte 4 of Byte5 Byte6 Address Dest MAC Dest MAC Read Destination OxCC 0x11 OxCC
35. op The radio will stay in Transmit mode until its session count expires When sending addressed packets session count is defined as session count refresh EEPROM address OxC4 number of transmit retries EEPROM address 0x4C When sending broadcast packets session count is equal to session count refresh EEPROM address OxC4 number of broadcast attempts EEPROM address Ox4D Once the radio exits the session it returns to the default Receive mode When sending an addressed packet the RF packet is sent only to the receiver specified in the Destination Address To increase the odds of successful delivery Transmit Retries are utilized Transparent to the OEM host the transmitting radio will send the RF packet to the remote transceiver If the remote transceiver receives the packet free of errors it will return an RF acknowledge to the transmitting radio within the same 50ms hop If a RF acknowledgement is not received the transmitting radio will use a transmit retry to resend the packet The transmitting radio will continue sending the packet until either 1 a RF acknowledgement is received or 2 all transmit retries have been used The remote transceiver will only send the received packet to the OEM host if and when it is received free of errors Note If Transmit Retries is set to 1 the radio will only attempt to send the data one time with no retries the minimum setting for Transmit Retries is 1 and cannot be set to 0 Addresse d Packe
36. packet times then retry 0x07 Wait 1 8 packet times then retry OxOF Wait 1 16 packet times then retry Ox1F Wait 1 32 packet times then retry Ox3F Wait 1 64 packet times then retry Ox7F Wait 1 128 packet times then retry OxFF Wait 1 256 packet times then retry Americas 1 800 492 2320 Option 2 25 Laird Technologies Europe 44 1628 858 940 Hong Kong 852 2923 0610 www lairdtech com ramp AC4790 User s Manual Version 2 0 Sense Adjust OxC8 1 0x00 Setin The minimum RSSI required by a transceiver OxFF production to establish a session upon hearing a long may vary beacon Probe Report OxC9 1 0x00 OxE3 When set to OxE3 upon receiving a probe OxFF the transceiver sends a Probe Report to the OEM host DES Key OxDO 7 0x00 56 bit Data Encryption key OxFF ORDERING INFORMATION Product Part Number Tree AC4790 XXXXX XXX Interface 485 2 Wire RS485 Blank 3 3V TTL Antenna Option A Integral Antenna 200 Only M MMCX Connector Blank AC4790 1x1 No Antenna Output Power 200 200 mW US Canada Only 1000 1000 mW 3 3V MMCX Only 1x1 Multichip Module 10 mW Figure 4 Product part number tree Developer Kit Part Numbers All of the above part numbers can be ordered as a development kit by prefacing the part number with SDK As an example part number AC4790 200A can be ordered as a development kit using the part number SDK AC4790 200A All developer s kits include
37. re of SS allows military or intelligence levels of privacy and security with minimal complexity While these characteristics may not be very important to everyday business or consumer needs these features are important to understand Frequency Hopping Spread Spectrum A FHSS radio does just what its name implies that is it hops from frequency to frequency over a wide band The specific order in which frequencies are occupied is a function of a code sequence and the rate of hopping from one frequency to another is a function of the information rate Americas 1 800 492 2320 Option 2 21 Laird Technologies Europe 44 1628 858 940 Hong Kong 852 2923 0610 www lairdtech com ramp AC4790 User s Manual Version 2 0 AC4790 Security Features As mentioned at the beginning of this section the AC4790 uses FHSS technology In addition Laird has implemented three levels of security in the AC4790 All three levels of security are associated with their own EEPROM parameter that can programmed for permanent operation or be changed during system operation in volatile memory The first two levels of security must be configured to establish a network of transceivers and are defined as the Channel Number and System ID The Channel Number represents a specific hopping sequence and provides physical separation between collocated networks Thus all transceivers in a network must be programmed to the same Channel Number There are a total of 48 Cha
38. rks of their respective holders This material is preliminary Information furnished by Laird Technologies in this specification is believed to be accurate Devices sold by Laird Technologies are covered by the warranty and patent indemnification provisions appearing in its Terms of Sale only Laird Technologies makes no warranty express statutory and implied or by description regarding the information set forth herein Laird Technologies reserves the right to change specifications at any time and without notice Laird Technologies products are intended for use in normal commercial and industrial applications Applications requiring unusual environmental requirements such as military medical life support or life sustaining equipment are specifically not recommended without additional testing for such application Limited Warranty Disclaimer Limitation of Liability Americas 1 800 492 2320 Option 2 33 Laird Technologies Europe 44 1628 858 940 Hong Kong 852 2923 0610 www lairdtech com ramp
39. rong remote heard local transceiver RSSI How strong local heard remote transceiver EEPROM Byte Read Upon receiving this command a transceiver will respond with the desired data from the addresses requested by the OEM host Command OxCC OCH Data Data2 Number of Bytes Returned 4 Response OxCC Data1 Data2 Data Parameter Range Datal EEPROM address Data2 Length 0x00 0x80 Data3 Requested data Americas 1 800 492 2320 Option 2 15 Laird Technologies Europe 44 1628 858 940 Hong Kong 852 2923 0610 www lairdtech com ramp AC4790 User s Manual Version 2 0 EEPROM Byte Write Upon receiving this command a transceiver will write the data byte to the specified address but will not echo it back to the OEM host until the EEPROM write cycle is complete up to 10ms Multiple byte writes of up to 128 bytes are allowed An EEPROM boundary exists between addresses Ox7F and 0x80 No single EEPROM write command shall write to addresses on both sides of that EEPROM boundary Command OxCC OxC1 Data Data2 Number of Bytes Returned 4 Response OxCC Data1 Data2 Data Parameter Range Data1 EEPROM address Data2 Length 0x00 0x80 Data3 Data written Reset The OEM host issues this command to perform a soft reset of the transceiver Any transceiver settings modified by CC commands will revert to the values stored in the EEPROM Command OxCC OxFF Number of Bytes Retur
40. rope 44 1628 858 940 Hong Kong 852 2923 0610 www lairdtech com ramp AC4790 User s Manual Version 2 0 Case 4 In this case a radio loads its Session Count with the remote radio s current Session Count This is suitable for daisy chain applications and large networks in which radios cannot stay in session longer than needed This case guarantees that two radios will stay in session as long as they have data to communicate and will both leave the session at the same time Receive Mode Pending data received over RF Discard Packet Discard Packet Broadcast Packet Receive Ful Packet Valid Addressed Packet CRC Matching Destination MAC Duplicate Packet Send Packet over UART to Host Duplicate Packet Send RF Acknowledge to sending transceiver Send Packet over UART to Host Figure 1 Pending RF data in buffer flow Americas 1 800 492 2320 Option 2 7 Laird Technologies Europe 44 1628 858 940 Hong Kong 852 2923 0610 www lairdtech com ramp AC4790 User s Manual Version 2 0 Command Mode A radio will enter Command Mode when data is received over the serial interface from the OEM host and either the Command Data pin pin 17 is logic Low or the received data contains the AT Enter AT Command Mode command Once in Command Mode all data received by the radio is interpreted as command data Command Data can be either EEPROM Configuration or On The Fly commanas Receive Mode
41. rst arrivals _ TBMA Efame GB1 Radio A Data GB2 Radio B Data GB3 Radio C Data GB4 1 Timeslot Figure 8 TDMA Timeslots Example 1 Shared Access Point SAP sends broadcast packet which includes a sync pulse 2 Remote radio9s hear the sync pulse and join the session 3 Radio A transmits during time interval t 1 4 Radio B transmits during time interval t 2 5 Radio N transmits during time interval t N 1 This type of implementation requires careful planning and should allow enough time for retries if necessary When full duplex is enabled the radio which initiated the session SAP will transmit during the even numbered hops and the remote radios will transmit only during odd numbered hops Americas 1 800 492 2320 Option 2 31 Laird Technologies Europe 44 1628 858 940 Hong Kong 852 2923 0610 www lairdtech com ramp AC4790 User s Manual Version 2 0 RELATED DOCUMENTS AND FILES The following additional AC4790 technical documents are also available from the Laird AC4790 product page under the Documentation tab AC4790 Product Brief AC4790 Hardware Integration Guide Statement of Compliance to EU WEEE Directive and RoHS Directive The following downloads are also available from the Laird RAMP modules Product Information page e Configuration Utility USB Drivers Americas 1 800 492 2320 Option 2 32 Laird Technologies Europe 44 1628 858 940 Ho
42. signals are intentionally made to be much wider band than the information they are carrying and use special pseudo noise codes to make them more noise like It is this very characteristic that makes SS signals difficult to detect intercept and demodulate SS signals are hard to detect on narrowband equipment because the signal s energy is soread over a much wider bandwidth Further SS signals are harder to jam interfere with than narrowband signals and have a much lower probability to be intercepted which is why the military has used spread spectrum for so many years The spread of energy over a wide band makes SS signals less likely to interfere with narrowband communications Narrowband communications conversely cause little to no interference to SS systems because the receiver effectively integrates the signal over a wide bandwidth to recover it Besides being hard to intercept and jam spread spectrum signals are hard to exploit or imitate Signal exploitation is the ability of a non network member to listen in to a network and use information from the network without being a valid network member or participant Imitation is the act of falsely or maliciously introducing false traffic or messages into a network SS signals are also naturally more secure than narrowband radio communications Thus SS signals can be made to have any degree of message privacy that is desired Messages can also be encrypted to any level of secrecy desired The very natu
43. ta bit 0 GOO bit 1 GO1 Americas 1 800 492 2320 Option 2 14 Laird Technologies Europe 44 1628 858 940 Hong Kong 852 2923 0610 www lairdtech com ramp AC4790 User s Manual Version 2 0 Probe Enabling bit 6 of API Control will enable this command When the OEM host issues this command the transceiver sends out a query every 500 ms The transceivers upon receiving the query randomly choose a query to respond to After responding to a Probe the transceiver will wait at least 10 seconds before responding to another probe Apart from the transceiver response there are two other responses that provide crucial information to the OEM host This information can be used to monitor the network and determine alternate routing paths Command OxCC Ox8E Data1 Number of Bytes Returned 2 Response OxCC Data1 Parameter Range 0x00 Disable Probe 0x01 Enable Probe Probe Report Remote transceiver s response to its OEM host upon receiving a Probe query Note Only valid when Probe Report address OxC9 is set to OxE3 Command N A Number of Bytes Returned 5 Response 0x86 RSSI MAC3 MAC2 MAC Parameter Range MAC3 MAC2 MAC1 3 LSB s of radio sending the Probe query Transceiver s Response Upon hearing the remote transceiver s probe acknowledge the transceiver responds to the OEM host Command N A Number of Bytes Returned 6 Response 0x87 RSSI RSSI MAC3 MAC2 MAC1 Parameter Range RSSI How st
44. ta Complete can be used as a software acknowledgement indicator When a radio sends an addressed packet it looks for a received acknowledgement transparent to OEM host If one is not received the packet will be retransmitted until one is received or all retries have been used For applications where data loss is not an option the OEM host may wish to monitor the acknowledgement process using the API Send Data Complete If an acknowledgement is not received Failure the OEM host can send the packet to the transceiver once again API Send Data Complete is enabled when bit 2 of the API Control byte is enabled The transceiver sends the OEM host the following data upon receiving an RF acknowledge or exhausting all attempts 0x82 RSSI RSSI 0x00 Failure 0x01 Success RADIO INTERFACE Interface Timeout EEPROM address 0x58 in conjunction with RF Packet Size EEPROM address Ox5B determines when a buffer of data will be sent out over the RF as a complete RF packet based on whichever condition occurs first Interface Timeout specifies a maximum byte gap between consecutive bytes When that byte gap is exceeded the bytes in the transmit buffer are sent out over the RF as a complete packet Interface Timeout is adjustable in 0 5ms increments and has a tolerance of 0 5ms Therefore the Interface Timeout should be set to a minimum of 2 The default value for Interface Timeout is 0x04 2ms and should be adjusted accordingly when changing
45. the transceiver baud rate RF Packet Size When the number of bytes in the transceiver transmit buffer equals RF Packet Size those bytes are sent out as a complete RF packet It is much more efficient to send a few large packets rather than several short packets as every packet the transceiver sends over the RF contains extra header bytes which are not included in the RF Packet Size RF packet size can be set to a maximum of 0x80 and must be set to a minimum of 0x06 in order to send the Enter AT Command mode command Americas 1 800 492 2320 Option 2 17 Laird Technologies Europe 44 1628 858 940 Hong Kong 852 2923 0610 www lairdtech com ramp AC4790 User s Manual Version 2 0 Flow Control Flow control refers to the control of data flow between transceivers It is the method used to handle data in the transmit receive buffer and determines how data flow between the transceivers is started and stopped Often one transceiver is capable of sending data much faster than the other can receive and flow control allows the slower device to tell the faster device when to pause and resume data transmission When a transceiver has data to send it sends a Ready To Send signal and waits for a Clear To Send response from the receiving unit If the receiving radio is ready to accept data it will assert its CTS Low CTS will be reasserted when the buffer contains the number of bytes specified by CTS_OFF EEPROM address Ox5D These signals are sent ap
46. tilizes a Frequency Hopping Spread Spectrum FHSS technology which provides the foundation for secure digital wireless communications The purpose of this section is to take a brief look at how spread spectrum technology works and explain how an OEM can enable specific security features available in the AC4790 Spread Spectrum History Spread Spectrum or SS signals dates back to World War Il when a female German scientist was granted a patent on a simple frequency hopping continuous wave CW system The allies also experimented with spread spectrum in World War Il These early research and development efforts tried to provide countermeasures for radar navigation beacons and communications The U S Military has used SS signals over satellites for at least 25 years How Spread Spectrum Works SS radio communications has long been a favorite technology of the military because it resists jamming and is hard for an enemy to intercept And now this very same technology is being widely used in the commercial industrial and even consumer markets The reason SS signals are distributed over a wide range of frequencies and then collected onto their original frequency at the receiver making them so inconspicuous as to be transparent Just as they are unlikely to be intercepted by a military opponent so are they unlikely to interfere with other signals intended for business and consumer users even ones transmitted on the same frequencies Spread
47. ts When sending a broadcast packet the RF packet is sent out to every eligible transceiver on the network To increase the odds of successful delivery Broadcast attempts are utilized Transparent to the OEM host the transmitting radio sends the RF packet to all remote Broadcast transceivers that are both in range and network unless they have Unicast Only enabled Packets Unlike Transmit Retries all Broadcast Attempts are used regardless of when the RF packet is actually received and without RF acknowledgements If the packet is received on the first attempt the remote transceiver will ignore the remaining broadcasts The received packet will only be sent to the OEM host if and when it is received free of errors Americas 1 800 492 2320 Option 2 5 Laird Technologies Europe 44 1628 858 940 Hong Kong 852 2923 0610 www lairdtech com ramp AC4790 User s Manual Version 2 0 Receive Mode If a transceiver detects a sync pulse addressed to itself or broadcast on its network while in Receive Mode it will join the Session and begin receiving data While in Receive Mode subsequent data of up to 128 bytes can be received every hop 50 ms When a transceiver is in Session its Session Count is decremented by one every hop When the Session Count reaches zero the transceiver exits the Session In order to continue receiving data the transceivers update their Session Count every time data or an RF acknowledge is received The SLockO
48. yte Command OxCC 0x16 Number of Bytes Returned 2 Response OxCC API Control Write API Control The OEM host issues this command to write the API Control byte Command OxCC 0x17 Number of Bytes Returned 2 Response OxCC API Control Americas 1 800 492 2320 Option 2 12 Laird Technologies Europe 44 1628 858 940 Hong Kong 852 2923 0610 www lairdtech com ramp AC4790 User s Manual Version 2 0 Set Max Power The OEM host issues this command to limit the maximum transmit power emitted by the transceiver This can be useful to minimize current consumption and satisfy certain regulatory requirements The radios are shipped at maximum allowable power Command OxCC 0x25 Max Power Number of Bytes Returned 2 Response OxCC Max Power Read Temperature The OEM host issues this command to read the onboard temperature sensor The transceiver reports the temperature in C where 0x00 0x80 corresponds to 0 80 C and where OxD8 0x00 corresponds to 40 0 C Command OxCC OxA4 Number of Bytes Returned 2 Response OxCC Temperature Parameter Range Temperature OxD8 0x80 Read Digital Inputs The OEM host issues this command to read the state of both digital input lines Command OxCC 0x20 Number of Bytes Returned 2 Response OxCC Data Parameter Range Data bit 0 GIO bit 1 G11 Read Radio Table The OEM host issues this command to read the Radio Table t
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