HS Series Encoder Module Data Guide Warning: Linx radio frequency ("RF") products may be ! used to control machinery or devices remotely, including machinery or devices that can cause death, bodily injuries, and/or property damage if improperly or inadvertently triggered, particularly in industrial settings or other applications implicating life-safety concerns. No Linx Technologies product is intended for use in any application without redundancies where the safety of life or property is at risk. The customers and users of devices and machinery controlled with RF products must understand and must use all appropriate safety procedures in connection with the devices, including without limitation, using appropriate safety procedures to prevent inadvertent triggering by the user of the device and using appropriate security codes to prevent triggering of the remote controlled machine or device by users of other remote controllers. Do not use this or any Linx product to trigger an action directly from the data line or RSSI lines without a protocol or encoder/ decoder to validate the data. Without validation, any signal from another unrelated transmitter in the environment received by the module could inadvertently trigger the action. This module does not have data validation built in. All RF products are susceptible to RF interference that can prevent communication. RF products without frequency agility or hopping implemented are more subject to interference. This module does not have frequency agility built in, but the developer can implement frequency agility with a microcontroller and the example code in Linx Reference Guide RG-00101. Do not use any Linx product over the limits in this data guide. Excessive voltage or extended operation at the maximum voltage could cause product failure. Exceeding the reflow temperature profile could cause product failure which is not immediately evident. Do not make any physical or electrical modifications to any Linx product. This will void the warranty and regulatory and UL certifications and may cause product failure which is not immediately evident. Table of Contents 1 Description 1 Features 2 Applications 2 Ordering Information 2 Absolute Maximum Ratings 3 Electrical Specifications 4 Recommende Pad Layout 4 Production Considerations 5 Pin Assignments 6 Encoder MODE_IND Indication Table 6 Pin Descriptions 8 Remote Control Overview 10 HS Series Overview 12 HS Series Security Overview 14 Encoder Operation 15 Encoder Get Key Mode 15 Encoder Send Mode 15 Encoder Create Pin Mode 18 Typical Application 19 Typical System Set Up 20 Design Steps to Using the HS Series 20 Key Creation and Exchange from a Decoder to an Encoder 21 Creation of Control Permissions 22 Creation of an Encoder PIN 23 Resources LICAL-ENC-MS001 YYWWNNN C S O M H P HS Series Encoder Module Data Guide Description 0.309 HS Series encoders and decoders are (7.85) 0.207 (5.25) 0.026 designed for maximum security remote control (0.65) applications. The HS encoder encodes the status of up to eight buttons or contacts into 0.284 a highly secure encrypted output intended for (7.20) 0.013 (0.32) wireless transmission via a RF or infrared link. The HS Series uses CipherLinx™ technology, which is based on the Skipjack algorithm developed by the U.S. National Security Agency (NSA) and has been independently evaluated 0.007 0.030 (0.18) by ISE. CipherLinx™ never sends or accepts (0.75) the same data twice, never loses sync, and changes codes on every packet, not just every Figure 1: Package Dimensions button press. In addition to state-of-the-art security, the tiny 20-pin SSOP packaged parts also offer innovative features, including up to 8 data EVALUATED lines, multiple baud rates, individual “button level” ® permissions, keypad user PIN, encoder identity CipherLinx output, low power consumption and easy setup. Technology EVALUATED Features TM • CipherLinx security technology • Encoder ID available at decoder • ISE evaluated • Wide 2.0 to 5.5V operating • Never sends the same packet voltage twice • Low supply current (370µA @ 3V) • Never loses sync • Ultra-low 0.1µA sleep current • PIN-protected encoder access • Selectable baud rates • 8 selectable data lines • No programmer required • "Button level" permissions • Small SMD package – – Revised 11/23/12 1 L I o A N R T Applications • Keyless entry / access control • Car alarms / starters • Door and gate openers • Home / industrial automation • Security systems • Remote status monitoring • Remote device control Ordering Information Ordering Information Part Number Description LICAL-ENC-HS001 HS Encoder LICAL-DEC-HS001 HS Decoder MDEV-LICAL-HS HS Master Development System HS encoders are shipped on reels of 1,600 Figure 2: Ordering Information Absolute Maximum Ratings Absolute Maximum Ratings Supply Voltage V −0.3 to +6.5 VDC CC Any Input or Output Pin −0.3 to V + 0.3 VDC CC Max. Current Sourced by Output Pins 25 mA Max. Current Sunk by Output Pins 25 mA Max. Current Into V 250 mA CC Max. Current Out Of GND 300 mA Operating Temperature −40 to +85 ºC Storage Temperature −65 to +150 ºC Exceeding any of the limits of this section may lead to permanent damage to the device. Furthermore, extended operation at these maximum ratings may reduce the life of this device. Figure 3: Absolute Maximum Ratings Encoder SEND to Decoder Activation Times (mS) Baud Rate Decoder Activation Time 4,800 67 28,800 36 Figure 4: Encoder SEND to Decoder Activation Times (mS) – – 2 Electrical Specifications HS Series Encoder Specifications Parameter Symbol Min. Typ. Max. Units Notes Power Supply Operating Voltage V 2.0 5.5 VDC CC Supply Current l CC At 2.0V V 240 300 µA 1 CC At 3.0V V 370 470 µA 1 CC At 5.0V V 670 780 µA 1 CC Power Down Current l PDN At 2.0V V 0.10 0.80 µA CC At 3.0V V 0.10 0.85 µA CC At 5.0V V 0.20 0.95 µA CC Encoder Section Input Low V 0.0 0.15 x V V 2 IL CC Input High V 0.8 x V V V 3 IH CC CC Output Low V 0.6 V OL Output High V V – 0.7 V OH CC Input Sink Current 25 mA Output Drive Current 25 mA SEND High to DATA_OUT 3.3 mS Environmental Operating Temperature Range –40 +85 °C 1. Current consumption with no active loads. 2. For 3V supply, (0.15 x 3.0) = 0.45V max. 3. For 3V supply, (0.8 x 3.0) = 2.4V min. Figure 5: Electrical Specifications Warning: This product incorporates numerous static-sensitive components. Always wear an ESD wrist strap and observe proper ESD handling procedures when working with this device. Failure to observe this precaution may result in module damage or failure. – – 3 Recommended Pad Layout HS Series encoders and decoders are implemented in an industry standard 20-pin Shrink Small Outline Package (20-SSOP). The recommended layout dimensions are shown in Figure 6. 0.047 (1.19) 0.016 (0.41) 0.026 (0.65) 0.234 (5.94) 0.328 (8.33) Figure 6: PCB Layout Dimensions Production Considerations These surface-mount components are designed to comply with standard reflow production methods. The recommended reflow profile is shown below and should not be exceeded, as permanent damage to the part may result. Lead-Free Sn / Pb 275 260°C Max 250 240°C Max 225 200 175 150 125 100 75 50 25 0 020406080 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 420 TIME (SECONDS) Figure 7: MT Series Reflow Profile – – 4 TEMPERATURE (°C) Pin Assignments 1 LICAL-ENC-MS001 20 D6 D5 2 19 D7 D4 3 18 SEL_BAUD0 D3 4 17 SEL_BAUD1 D2 5 16 GND VCC 6 15 GND VCC 7 14 GND D1 8 13 TX_CNTL D0 9 12 DATA_OUT SEND 10 11 MODE_IND CREATE_ADDR Figure 8: HS Series Encoder Pin Assignments Pin Descriptions Pin Number Name I/O Description 1, 2, 13, 14, D0–D7 I Data Input Lines 17–20 3 SEL_BAUD I Baud Rate Selection Line 4 SEL_TIMER I PIN Time-Out Timer Select Line 5, 6 GND Ground 7 KEY_IN I Key Input Pin 8 TX_CNTL O External Transmitter Control Line 9 DATA_OUT O Serial Data Output 10 MODE_IND O Mode Indicator Output 11 CREATE_PIN I Create PIN Mode Selection Line 12 SEND I Encoder Send Data Line 15, 16 V Positive Power Supply CC None of the input lines have internal pull-up or pull-down resistors. The input lines must always be in a known state (either GND or V ) at all times or the operation may not be CC predictable. The designer must ensure that the input lines are never floating, either by using external resistors, by tying the lines directly to GND or V , or by use of other circuits to CC control the line state. Figure 9: Pin Descriptions – – 5 Encoder MODE_IND Indication Table The MODE_IND line is the primary means of indicating the state of the encoder to the user. The table below provides definitions for the MODE_ IND signals. HS Series Encoder MODE_IND Definitions MODE_IND Signal Definition Get Key Mode ON for 1 second after a successful key transfer. Flashes* for 15 seconds while waiting for user Create PIN Mode to enter a PIN. It stops flashing when the fourth number is entered or when it times out. Enter PIN Mode ON when each PIN is entered. *Flash = ON for 200ms and OFF for 200ms Figure 10: HS Series Encoder MODE_IND Definitions Pin Descriptions Data Lines The encoder has eight data lines, D0 through D7. when the SEND line goes high, the states of these lines are recorded, encrypted for transmission, then reproduced on the outputs of the decoder. SEL_BAUD This line is used to select the baud rate of the serial data stream. The state of the line allows the selection of one of two possible baud rates, as shown in Figure 11. Baud Rate Selection Table SEL_BAUD Baud Rate (bps) 0 4,800 1 28,800 Figure 11: Baud Rate Selection Table The baud rate must be set before power-up. The encoder will not recognize any change in the baud rate setting after it is on. – – 6 SEL_TIMER This line is used to set the length of inactive time before PIN reentry is required. GND These lines are connected to ground. KEY_IN This line is used to input the key from the decoder TX_CNTL This line goes high when the SEND line goes high and low when the SEND line goes low. This can be used to power up external devices, such as a transmitter, when the encoder is sending data, and power it down when the encoder is asleep. It can also be used to drive a LED for visual indication of transmission. DATA_OUT The encoder will output an encrypted serial data stream on this line. This line can directly interface with all Linx RF transmitter modules or it can be used to modulate an IR diode. MODE_IND This line will be activated while the encoder is in Get Key Mode or Create Pin Mode. It allows the connection of a LED or other indicator for user feedback. CREATE_PIN When this line is taken high, the encoder will enter Create PIN Mode and allow the user to set a Personal Identification Number (PIN) to control encoder access. SEND When this line goes high, the encoder will record the states of the data lines, encrypt them for transmission, and send the packet as a serial bit stream through the DATA_OUT line at the baud rate selected by the state of the SEL_BAUD line. V CC This is the positive power supply. – – 7 Remote Control Overview Wireless remote control is growing in popularity and finding its way into more unique applications. Remote Keyless Entry (RKE) systems for unlocking cars or opening garage doors quickly come to mind, but how about a trash container that signals the maintenance office when it needs to be emptied? The idea behind remote control is simple: a button press or contact closure on one end causes some action to be taken at the other. Implementation of the wireless RF stage has traditionally been complicated, but with the advent of simpler discrete solutions and modular products, such as those from Linx, implementation has become significantly easier. Encoder and decoder ICs are generally VCC employed to maintain the security and uniqueness of a wireless RF or IR ENC Tx link. These devices encode the status HS LR of inputs, usually button or contact Series Series closures, into a data stream suitable for wireless transmission. Upon successful recovery and Rx DEC validation, the decoder’s outputs are set LR HS GND to replicate the states of the Series Series encoder’s inputs. These outputs can then be used to control the circuitry Figure 12: Remote Control Block Diagram required by the application. Prior to the arrival of the Linx HS Series, encoders and decoders typically fell into one of two categories. First were older generation, low-security devices that transmitted a fixed address code, usually set manually with a DIP switch. These products were easy to use, but had significant security vulnerabilities. Since they sent the same code in every transmission, they were subject to code grabbing. This is where an attacker records the transmission from an authorized transmitter and then replays the transmission to gain access to the system. Since the same code is transmitted every time, the decoder has no way to validate the transmission. – – 8 These concerns resulted in the development of a second type of encoder and decoder that focused on security and utilized a changing code to guard against code grabbing. Typically, the contents of each transmission changes based on complex mathematical algorithms to prevent someone from reusing a transmission. These devices gained rapid popularity due to their security and the elimination of manual switches; however, they imposed some limitations of their own. Such devices typically offer a limited number of inputs, the transmitter and receiver can become desynchronized, and creating relationships and associations among groups of transmitters and receivers is difficult. The HS Series offers the best of all worlds. The HS Series uses an advanced high security encryption algorithm called CipherLinx™ that will never become desynchronized or send the same packet twice. It is easily configured without production programming and allows for “button level” permissions and unique encoder and decoder relationships. Eight inputs are available, allowing a large number of buttons or contacts to be connected. To learn more about different encoder and decoder methodologies, please refer to Application Note AN-00310. – – 9 HS Series Overview The HS Series encoder encrypts the status of up to eight buttons or contacts into highly secure encrypted serial data stream intended for wireless transmission via an RF or infrared link. The series uses CipherLinx™ technology, which is based on the Skipjack algorithm developed by the United States National Security Agency (NSA). The CipherLinx™ protocol in the HS Series has been independently evaluated by Independent Security Evaluators (ISE). A full evaluation white paper is available at www.linxtechnologies.com/cipherlinx. The encoder combines eight bits representing the state of the eight data lines with counter bits and integrity bits to form a 128-bit message. To prevent unauthorized access, this message is encrypted with CipherLinx™ in a mode of operation that provides data integrity as well as secrecy. CipherLinx™ never sends or accepts the same data twice, never loses sync, and changes codes with every packet, not just every button press. Decoding of the received data signal is accomplished by a corresponding Linx HS Series decoder. When the decoder receives a valid command from an encoder, it will activate its logic-level outputs, which can be used to control external circuitry. The encoder will send data continuously as long as the SEND line is held high. Each time the algorithm is executed, the counter is decremented, causing the code to be changed with the transmission of each packet. This, combined with the large counter value and the timing associated with the protocol, ensures that the same transmission is never sent twice. An 80-bit key used to encrypt the data is created in the decoder by the user. The decoder is placed into Create Key Mode, and a line is toggled 10 times, usually by a button. This is required to gather entropy to ensure that the key is random and chosen from all 280 possible keys. A high-speed timer is triggered by each rise and fall of voltage, recording the time that the line is high and low. The 80-bit key is generated by combining the low-order bits of the twenty timer values. To create an association, the key, a 40-bit counter, and a decoder-generated ID are sent to the encoder via a wire, contacts, IR, or other secure serial connection. The HS Series allows the end user or manufacturer to create associations between the encoder and decoder. If the encoder and decoder have been associated through a successful key exchange, then the decoder will respond to the encoder’s commands based on its permissions. If an – – 10 encoder has not been associated with a decoder, its commands will not be recognized. The user or manufacturer may also set “button level” permissions. Permission settings control how the decoder will respond to the reception of a valid command, either allowing the activation of an individual data line or not. The decoder is programmed with the permission settings during set-up, and those permissions are retained in the decoder’s non-volatile memory. The HS decoder has the ability to identify and output a decoder-assigned identification number for a specific encoder. An encoder’s key, a 40-bit counter, and permissions are stored in one of fifteen memory locations within the decoder. The decoder is able to output an 8-bit binary number that corresponds to the memory location of the encoder’s information. This provides the ability to identify the specific encoder from which a signal originated. This identification can be used in various ways, including systems that record access attempts or in applications where the originating user needs to be known. – – 11 HS Series Security Overview Encryption algorithms are complex mathematical equations that use a number, called a key, to encrypt data before transmission. This is done so that unauthorized persons who may intercept the transmission cannot access the data. In order to decrypt the transmission, the decoder must use the same key that was used to encrypt it. The decoder will perform the same calculations as the encoder and, if the key is the same, the data will be recovered. The HS Series uses the CipherLinx™ algorithm, which is based on Skipjack, a cipher designed by the U.S. National Security Agency (NSA). At the time of this writing, there are no known cryptographic attacks on the full Skipjack algorithm. Skipjack uses 80-bit keys to encipher 64-bit data blocks. The CipherLinx™ algorithm uses Skipjack in a provably secure authenticated encryption mode both to protect the secrecy of the data and ensure that it is not modified by an adversary. 8 bits of data are combined with a 40-bit counter and 80 bits of integrity protection before being encrypted to produce each 128-bit packet. Preamble 128-Bit Encrypted Data RX Noise Logic Integrity Check Data Counter Balancing Filter Filter 80 bits 8 bits 40 bits Figure 13: HS Series Data Structure There are several methods an attacker may use to try to gain access to the data or the secured area. Because a key is used to interpret an encrypted message, trying to find the key is one way to attack the protected message. The attacker would either try using random numbers or go through all possible numbers sequentially to try to get the key and access the data. Because of this, it is sometimes believed that a larger key size will determine the strength of the encryption. This is not entirely true. Although it is a factor in the equation, there are many other factors that need to be included to maintain secure encryption. One factor is the way that the underlying cipher (in the case of the CipherLinx™ algorithm, Skipjack) is used to encrypt the data. This is referred to as the cipher’s “mode of operation.” If a highly secure cipher is used in an insecure mode, the resulting encryption will be insecure. For example, some encryption modes allow an adversary to combine parts of legitimate encrypted messages together to create a new (and possibly malicious) encrypted message. This is known as a “cut-and-paste” attack. – – 12 The mode of operation used by the CipherLinx™ algorithm is proven to prevent this type of attack. Another critical factor is how often the message changes. To prevent code grabbing, most high-security systems send different data with each transmission. Some remote control applications will encrypt the message once per activation and repeat the same message over again until it is deactivated. This gives an attacker the opportunity to copy the message and retransmit it to maintain the state of the protected device and “hold the door open”, or worse yet, have the option to come back later and gain access. The HS Series goes a step further and sends different data with EACH PACKET, so the data will change continuously during each transmission. This means that at 28,800bps, there will be a completely new 128-bit message sent every 25.5mS. Another factor is how often the message will be repeated and the intervals between repeats. Some applications use a counter to change the appearance of the message. This is good, but at some point, the counter will roll over and the message will be repeated. For example, if attackers were to copy an encrypted message and save it, they could potentially gain access to the protected device at a later time. Depending on the size of the counter, this vulnerability could occur frequently. The HS Series uses a 40-bit decrementing counter to keep this from ever happening. If the SEND line was held high continuously at the high baud rate (28,800bps), it would take 889 years before the counter would reach zero, at which point the key would be erased and the encoder would have to get a new key. The math used is: [(240 * 25.5ms) / (1000mS*60s*60m*24h*365d)] = 889 years. This large counter prevents a packet from ever being sent twice and prevents the encoder from ever losing sync with the decoder. The key is generated with the decoder by the user through multiple button presses. This is ensures that the key is random and chosen from all 280 possible keys. Since all of the keys are created by the user and are internal to the part, there is no list of numbers anywhere that could be accessed to compromise the system. Encryption of the transmitted data is only one factor in the security of a system. With most systems, once an encoder is authorized to access a decoder, it can activate all of the decoder data lines. With the HS Series, each encoder can be set to only activate certain lines. This means that the same hardware can be set up with multiple levels of control, all at the press of a button. – – 13 Another factor in system security is the control of the encoder. If attackers gain control of the encoder, typically they would be able to access the system. The HS offers the option of adding a Personal Identification Number (PIN) to the encoder that must be entered before the encoder will activate. Furthermore, since each encoder has its own key and the Control Permissions are stored in the decoder, all the attackers would be able to do is duplicate the device that they have already taken. They will not be able to grant themselves greater authority, create a new controller, or replicate another encoder. Before the encoder sends a packet, it will calculate the Hamming Weight (the number of ‘1’s in the string) of the packet to determine the duty cycle. If the duty cycle is greater than 50% (more ‘1’s than ‘0’s), the encoder will logically invert all of the bits. This ensures that every packet will always contain 50% or less ‘1’s. Since the FCC allows transmitter output power to be averaged over 100mS, this allows a legal improvement in link range and performance for many devices using an ASK / OOK transmitter. A 50% duty cycle is generally the best compromise between data volume and output power. Some other manufacturers may use a Pulse Width Modulation (PWM) scheme or Manchester Encoding scheme to maintain a 50% duty cycle. Both of these methods work, but are inefficient and do not make use of the full link budget. The HS Series uses true serial data while maintaining a 50% duty cycle. Application Note AN-00310 covers these issues in detail. Encoder Operation Upon power-up, the encoder sets the baud rate based on the state of the SEL_BAUD line, pulls the TX_CNTL line low, and goes into a low-power sleep mode. It will remain asleep until either the KEY_IN, SEND, or CREATE_PIN line goes high. These lines place the encoder in either Get Key Mode, Send Mode, or Create PIN Mode as described in the following sections. – – 14 Encoder Get Key Mode When the encoder registers activity on the KEY_IN line, it will enter Get Key Mode. In this mode, the encoder will look for an encryption key and user ID from a decoder. When it receives this information, it will send a confirmation on the DATA_OUT line to the decoder. It will then look for a final confirmation from the decoder on the KEY_IN line. Once this confirmation is received, the encoder will take the MODE_IND line high for one second to indicate that the key has been successfully transferred and that the units may now work together. Encoder Send Mode When the SEND line goes high, the encoder will enter Send Mode. It will pull the TX_CNTL line high to activate the transmitter and record the state of the data lines. The encoder will then encrypt the data using the saved key and send it through the DATA_OUT line. It will continue doing this for as long as the SEND line is high, updating the state of the data lines with each transmission. Once SEND is pulled low, the encoder will finish the current transmission, pull TX_CNTL low to deactivate the transmitter, and go to sleep. For simple applications that require only a single input, SEND can be tied directly to the data input line, allowing a single connection. If additional lines are used in this manner, diodes or dual contact switches will be necessary to prevent voltage on one data line from activating all of the data lines. The Typical Applications section of this data guide demonstrates the use of diodes for this purpose. Encoder Create Pin Mode For higher security applications, the HS Series encoder has the option to set a Personal Identification Number (PIN) to control access to the encoder. This PIN is a four-digit combination of the eight data lines that must be entered before the encoder will transmit any commands to the decoder. Create PIN Mode is entered by pressing the CREATE button on the encoder. The MODE_IND line will begin flashing to indicate that the encoder is ready for the PIN to be entered. The user will have 15 seconds to press any 4-button combination to set the PIN. After the fourth button press, the MODE_IND line will go low. If 4 buttons are not pressed or the CREATE line goes high within the 15 second window, no PIN will be set. Once created, the PIN can be erased only by learning a new key from the decoder. – – 15 Once the PIN has been set, the user must enter it correctly before the encoder will transmit any commands. When entered, the encoder will be active for a period of time set by the SEL_TIMER line. If this line is connected to ground, the PIN will need to be entered after 15 minutes of inactivity. If this line is high, the PIN will need to be entered after 30 seconds of inactivity. If no PIN is set, then the encoder will activate as soon as the SEND line goes high. – – 16 Power Up Set Baud Rate Pull The TX_CNTL Line low Go To Sleep & Wake On Interrupt Is The Is The Is The NO NO NO KEY_IN Line CREATE_PIN SEND Line High? Line High? High? YES YES YES Pull The TX_CNTL Line High Set Timer YES NO Is PIN Is PIN Active? Enabled? Pull The DATA Line High YES YES NO Time Out? Get Data Byte Set 15-Second Timer Is PIN YES NO Active? Create Packet Toggle MODE_IND Line NO Is The NO KEY_IN Line Pull The DATA High? Line Low Set Timer To 2S 15 Second YES Timer Time YES Out? Send Packet YES Did The Timer NO NO Is The Expire? Data Valid? Is The YES Is The SEND Line YES NO CREATE Line High? YES High? Pull The TX_CNTL NO Line High Was A Button NO NO Pressed? NO Get Data Is PIN NO Was A Button Enabled? YES Pressed? Was The YES NO YES 4th Button NO Is The Pull The TX_CNTL Pressed? Data Valid? Line Low Was The NO YES 4th Button YES Pressed? Set Timer From SEL_TIMER Line Did NO Does PIN YES Send And NO Match? Receive Confirmation Save PIN Is The Pass? YES SEND Line YES High? YES Save Data NO Pull MODE_IND Did The Timer NO High For 1 Second Expire? YES Figure 14: HS Series Encoder Flowchart – – 17 Typical Application The HS Series encoder is ideal for registering button presses in secure remote control applications. An example application circuit is shown in Figure 15. 100k 100k 1 LICAL-ENC-HS001 20 D6 D5 100k 100k 2 19 D7 D4 100k 3 18 SEL_BAUD D3 100k 4 17 SEL_TIMER D2 5 16 GND VCC 6 15 GND VCC 100k 7 14 From Key Input Port KEY_IN D1 100k 8 13 To Transmitter PDN TX_CNTL D0 9 12 220 To Transmitter DATA_OUT SEND 100k 220 10 11 MODE_IND CREATE_PIN 100k Figure 15: HS Series Encoder Application Circuit In this example, the data lines are connected to buttons, and when any button is pressed, the SEND line is pulled high and causes the encoder to transmit. Diodes are used to prevent the voltage on one data line from affecting another. The KEY_IN line is attached to a port that allows the key to be transferred from the decoder during setup. To ensure security, this would normally be a wire, contact, or short range IR link, although any connection capable of transferring asynchronous serial data may be utilized. None of the inputs have pull-up or pull-down resistors internally, so 100kΩ pulldown resistors are used on the data, SEND, and CREATE_PIN lines. These resistors are used to pull the lines to ground when the buttons are not being pressed, which ensures that the pins are always in a known state and not floating. Without these resistors, the state of the lines cannot be guaranteed and encoder operation may not be predictable. A LED is attached to the MODE_IND line to provide visual feedback to the user that an operation is taking place. This line will source a maximum of 25mA, so the limiting resistor may not be needed, depending on the LED chosen and the brightness desired. A LED can also be connected to the TX_CNTL line to provide visual indication that the encoder is sending data. Outgoing encrypted data will be sent via the DATA_OUT line at the baud rate determined by the state of the SEL_BAUD line. In the circuit above, the – – 18 baud has been set for 4,800bps by pulling it to ground. The DATA_OUT line can be connected directly to the DATA_IN line of a Linx transmitter or other wireless device. The TX_CNTL line may be connected to the PDN line of a Linx transmitter so that the module will enter a low power state when not in use. In this example, the data lines are pulled high by simple pushbutton switches, but many other methods may be employed. Contacts, reed switches, or microcontrollers are just some examples of other ways to pull the data lines high. The flexibility of the encoder, combined with the associative options of the matching decoder, opens a new world of options for creative product designers. Typical System Setup The HS Series offers an unmatched combination of features and security, yet is easy for system designers and end users to operate. To demonstrate this, let’s take a brief look at a typical user setup followed by more detailed design information. The Typical Applications sections of the encoder and decoder data guides show the circuit schematics on which these examples are based. 1. Create and exchange a key from a decoder to an encoder. The high security key is created and exchanged by placing the decoder in the Create Key Mode. The decoder’s MODE_IND line LED will light to indicate that the decoder has entered Create Key Mode. The decoder’s CREATE_KEY button is then pressed ten times to create the key. After the tenth press, the MODE_IND LED will turn off and the decoder will send the key out of the KEY_OUT line. The MODE_IND LED on the encoder will light to indicate that the key has been successfully transferred. 2. Establish Control Permissions The user establishes what buttons on the encoder will be recognized by pressing the decoder LEARN button. The decoder’s MODE_IND LED will start flashing and the user presses the buttons that will be allowed access. Control Permissions are stored when the LEARN button is pressed again or automatically after 17 seconds. There are other powerful options such as programming a user PIN or copying a decoder but these simple steps are all that is required for a typical setup. It is really that simple for a manufacturer or end user to setup the product! – – 19 Design Steps to Using the HS Series Key Creation and Exchange from a Decoder to an Encoder. 2 DATA OUT DATA IN 4 MODE_IND CREATE KEY BUTTON 3 LEARN BUTTON SEND COPY BUTTON 1 KEY IN KEY OUT Figure 16: Steps to Exchange a Key Provide a serial data connection from the decoder’s KEY_OUT line to the encoder’s KEY_IN line. Typically this would be a wire, contact, or infrared. 1. Provide a serial data connection from the encoder’s DATA_OUT line DATA OUT DATA IN to the decoder’s DATA_IN line. Typically, this would be a wireless connection using a transmitter and receiver combination. MODE_IND 2. On the decoder, set the LEARN line high and then the CREATE_KEY 2 line high to enter Create Key Mode. Take the LEARN line low, and CREATE KEY BUTTON 4 1 toggle the CREATE_KEY line high and low ten times to generate the LEARN BUTTON 3 key. SEND COPY BUTTON KEY IN KEY OUT 3. The encoder and decoder will automatically exchange the key using the DATA_OUT / DATA_IN and KEY_OUT / KEY_IN lines. If the key exchange is successful, the decoder and encoder MODE_IND lines will go high for 1 second. DATA IN DATA IN DEC A DEC B 3 3 MODE_IND MODE_IND CREATE KEY BUTTON CREATE KEY BUTTON 4 LEARN BUTTON LEARN BUTTON 2 SEND COPY BUTTON SEND COPY BUTTON COPY IN KEY OUT 1 KEY OUT COPY IN GROUND GROUND – – 20 2 DATA OUT DATA IN 4 MODE_IND CREATE KEY BUTTON 3 LEARN BUTTON SEND COPY BUTTON 1 KEY IN KEY OUT Creation of Control Permissions DATA OUT DATA IN MODE_IND 2 CREATE KEY BUTTON 4 1 LEARN BUTTON 3 SEND COPY BUTTON KEY IN KEY OUT Figure 17: Steps to Create Control Permissions 1. On the decoder, set the LEARN line high, then take it low to enter Learn Mode. DATA IN DATA IN DEC A DEC B 2. While the decoder’s MODE_IND line is toggling high / low, set a data line on the encoder high, then low. Repeat for each line to which 3 3 permission will be granted. MODE_IND MODE_IND CREATE KEY BUTTON CREATE KEY BUTTON 3. After all the desired data lines have been selected, set the LEARN line 4 LEARN BUTTON LEARN BUTTON high, then low again, or wait until the 17-second time-out occurs. The 2 permissions will now be saved in the decoder SEND COPY BUTTON SEND COPY BUTTON . COPY IN KEY OUT 4. Select the data lines during an actual transmission to confirm that the 1 KEY OUT COPY IN permissions have been successfully created. GROUND GROUND – – 21 Using the Optional Encoder Pin Creation of an Encoder Pin 1. Set the CREATE line high, then low to enter Create PIN Mode. The MODE_IND line will begin toggling high / low until either a PIN is success- MODE_IND fully entered or 15 seconds has passed. 2. To enter the PIN, set high then low a sequence 2 of any four data lines. The MODE_IND will stop 4 toggling and the PIN will be created. } 3. To cancel the Create PIN Mode prior to the 1 CREATE fourth entry, either wait for the 15 second time- 3 KEY IN out to pass or set and clear the CREATE line. The MODE_IND will stop toggling and no PIN Figure 18: Encoder PIN Setup will be created. 4. If a new KEY is created, the PIN will be automatically erased. Using the PIN 1. The PIN is entered by setting each data line high, then taking it low until all four entries have been made. There is a maximum 2-second time limit between entries after which the PIN must be reentered in its entirety. DATA OUT 2. Once the PIN is successfully entered, the encoder will be operational unless it is inactive for a period longer than what is chosen by the SEL_ TIMER line, in which case PIN reentry would be necessary. MODE_IND 2 } CREATE KEY IN – – 22 Resources Support For technical support, product documentation, application notes, regulatory guidelines and software updates, visit www.linxtechnologies.com RF Design Services For customers who need help implementing Linx modules, Linx offers design services including board layout assistance, programming, certification advice and packaging design. For more complex RF solutions, Apex Wireless, a division of Linx Technologies, creates optimized designs with RF components and firmware selected for the customer’s application. Call +1 800 736 6677 (+1 541 471 6256 if outside the United States) for more information. Antenna Factor Antennas Linx’s Antenna Factor division has the industry’s broadest selection of antennas by for a wide variety of applications. For customers with specialized needs, custom antennas and design services are available along with simulations of antenna performance to speed development. Learn more at www.linxtechnologies.com. – – 23 Linx Technologies 159 Ort Lane Merlin, OR, US 97532 3090 Sterling Circle, Suite 200 Boulder, CO 80301 Phone: +1 541 471 6256 Fax: +1 541 471 6251 www.linxtechnologies.com Disclaimer Linx Technologies is continually striving to improve the quality and function of its products. For this reason, we reserve the right to make changes to our products without notice. The information contained in this Data Guide is believed to be accurate as of the time of publication. Specifications are based on representative lot samples. Values may vary from lot-to-lot and are not guaranteed. “Typical” parameters can and do vary over lots and application. Linx Technologies makes no guarantee, warranty, or representation regarding the suitability of any product for use in any specific application. It is Customer’s responsibility to verify the suitability of the part for the intended application. At Customer’s request, Linx Technologies may provide advice and assistance in designing systems and remote control devices that employ Linx Technologies RF products, but responsibility for the ultimate design and use of any such systems and devices remains entirely with Customer and/or user of the RF products. LINX TECHNOLOGIES DISCLAIMS ANY AND ALL WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL LINX TECHNOLOGIES BE LIABLE FOR ANY CUSTOMER’S OR USER’S INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF OR RELATED TO THE DESIGN OR USE OF A REMOTE CONTROL SYSTEM OR DEVICE EMPLOYING LINX TECHNOLOGIES RF PRODUCTS OR FOR ANY OTHER BREACH OF CONTRACT BY LINX TECHNOLOGIES. CUSTOMER AND/OR USER ASSUME ALL RISKS OF DEATH, BODILY INJURIES, OR PROPERTY DAMAGE ARISING OUT OF OR RELATED TO THE USE OF LINX TECHNOLOGIES RF PRODUCTS, INCLUDING WITH RESPECT TO ANY SERVICES PROVIDED BY LINX RELATED TO THE USE OF LINX TECHNOLOGIES RF PRODUCTS. LINX TECHNOLOGIES SHALL NOT BE LIABLE UNDER ANY CIRCUMSTANCES FOR A CUSTOMER’S, USER’S, OR OTHER PERSON’S DEATH, BODILY INJURY, OR PROPERTY DAMAGE ARISING OUT OF OR RELATED TO THE DESIGN OR USE OF A REMOTE CONTROL SYSTEM OR DEVICE EMPLOYING LINX TECHNOLOGIES RF PRODUCTS. The limitations on Linx Technologies’ liability are applicable to any and all claims or theories of recovery asserted by Customer, including, without limitation, breach of contract, breach of warranty, strict liability, or negligence. Customer assumes all liability (including, without limitation, liability for injury to person or property, economic loss, or business interruption) for all claims, including claims from third parties, arising from the use of the Products. Under no conditions will Linx Technologies be responsible for losses arising from the use or failure of the device in any application, other than the repair, replacement, or refund limited to the original product purchase price. Devices described in this publication may contain proprietary, patented, or copyrighted techniques, components, or materials. © 2012 Linx Technologies. All rights reserved. The stylized Linx logo, Wireless Made Simple, CipherLinx, WiSE and the stylized CL logo are trademarks of Linx Technologies. – – 24