Congratulations on your purchase of the Atmel® AVR®-based Uni-directional Radio Starter Kit featuring
Secure Rolling Code RF Transmission Encryption. This kit uses an Atmel STK
troller Starter Kit that must be obtained separately.
This User’s Guide describes how to use this Starter Kit. Section 2, Getting Started, describes how to
assemble and program the hardware to demonstrate a wireless link that uses a secure rolling code algo
rithm. Section 3, Programming Notes, describes optional programming for the advanced user.
1.1Purpose
This starter kit demonstrates a Secure Rolling Code Algorithm transmission protocol for use in a unidirectional wireless communication system. Typical applications for this algorithm are garage door
openers, remote keyless entry, passive entry, and remote car-start systems.
1.2General Description
This kit demonstrates the transmission protocol with one receiver and a pair of associated transmitters.
However, a typical system can support many more transmitters.
Characteristics of this protocol are:
A transmission-encryption value that is valid only once, preventing interception and re-transmission to
gain unauthorized access,
Message content that is virtually impossible to predict, even if previous messages are known.
®
500 Flash Microcon-
-
For a thorough technical coverage of the hardware, software, and theory, read the application note,
“AVR411: Secure Rolling Code Algorithm for Wireless Link” that is included on the accompanying CD.
1.3Evaluation Kit Features
Advanced Encryption Standard (AES) and its Cipher-based Message Authentication Code (CMAC)
mode of operation for transmitter authentication:
Multiple transmitters supported
PC command-line tools for cryptographic key management
Up to 256-bit key sizes supported
Less than 30 ms response time
315/434/868 MHz ISM-band frequencies
ATA5771/73/74 and ATA8741/42/43 UHF ASK/FSK transmitters with embedded ATtiny44
microcontroller
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Introduction
ATA5723/24/28 and ATA8203/04/05 UHF ASK/FSK receivers
User-programmable transmitters with 6-pin ISP
Sleep modes for minimal power consumption
1.4Included in the Kit
Note:This Radio Starter Kit is not self-contained. It is based on an Atmel STK500 Flash Microcontroller Starter
Kit that must be obtained separately.
This starter kit includes all the essential components needed to demonstrate an AVR-based uni-directional radio that features a Secure Rolling-Code RF Transmission Encryption protocol. Contents of this
kit are listed and shown in
Transmitter application board
ISP programming adapter for Transmitter
Receiver application board with external antenna
STK512 Interface Board
ATMega88 microcontroller (not shown)
CDROM containing software, Data Sheets, and other documentation (not shown)
Figure 1-1.
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Figure 1-1. Kit Contents
Introduction
For investigating further capabilities of this kit, the following are optional:
JTAGICE mkII for debugging
IAR Embedded Workbench
®
AVR C compiler for changing and recompiling the source code without
porting it to another compiler (precompiled source code with default configuration is provided on the
CDROM).
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This section contains the steps required to get a simple system with a receiver and two transmitters up
and running. Hardware assembly, initial programming of the components, teaching the transmitters to
the receiver, and demonstrating the transmission protocol are described in the following subsections.
2.1Hardware Assembly
The kit hardware must be interfaced to the STK500.
Step A: Assemble the STK500 Board
The STK500 Board must be set up properly before mounting the STK512 Interface Board. The assembled STK500 Board is shown in Figure 2-1.
Figure 2-1. STK500 Board with Ribbon Cables and Microcontroller
Section 2
Getting Started
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Getting Started
1. Carefully remove any ICs in the green “SCKT3200A2” socket.
2. Insert the furnished ATMega88 into the “SCKT3200A2” socket.
Note:The orientation of the red stripe in the cable is not critical in the following steps as long as pin 1 is con-
nected to pin 1.
3. Using a 6-pin jumper cable supplied with the STK500;
connect the two male headers “ISP6PIN” and “SPROG2”.
4. Using a 10-pin jumper cable supplied with the STK500;
connect the two male headers “PORTC” and “LEDS”.
5. Using a 10-pin jumper cable supplied with the STK500;
connect the two male headers “PORTD” and “SWITCHES”.
6. Place jumpers on the following headers as shown in Figure 2-2.
–VTARGET
–AREF
– RESET
–XTAL1
– OSCEL (a 3-pin header. Place a jumper next to the “1” printed on the board).
Figure 2-2. Detail of Jumper Placement on the STK500
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Getting Started
Step B: Assemble and Attach the STK512 Interface Board
The STK512 Interface Board must be assembled and mounted on the STK500 Board. The completed
assembly is shown in
Figure 2-3.
Figure 2-3. Assembled STK512 Interface Board
1. Orient the STK500 as shown in the Figure 2-3.
Caution: After the next step, whenever the interface board is removed from the STK500 sockets, use
caution if a tool is used for leverage. It is easy to bend pins or otherwise damage the STK500 and/or the
interface board. Use a rocking motion while steadily pulling (not prying) it straight from the sockets.
2. Insert the STK512 Interface Board into the EXPANDx sockets, oriented with the LEDs and red DIP
switches to the left-hand side. To verify the orientation, check that the EXPAND0 pins on the Interface Board plug into the EXPAND0 socket on the STK500 Board. Press firmly so that the board pins
seat well.
3. Install jumpers on all five pairs of pins (JP2, next to the “configure” button) as shown in Figure 2-4.
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Getting Started
Figure 2-4. STK512 Jumper Placement
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Getting Started
Step C: Mount the Receiver Application Board
The Receiver Application Board must be mounted on the STK512 Interface Board. The completed
assembly is shown in
Figure 2-5.
Figure 2-5. Completed Receiver Assembly
Caution: After the next step, if the receiver board is removed from the interface board sockets, use
EXTREME caution! The pins on the receiver board are very easily bent and broken! Use a rocking
motion to lift the board straight (perpendicular) out of the socket.
1. Orient the receiver board above the Interface Board as shown in Figure 2-5. Carefully insert the
Receiver Application Board into the STK512 Interface Board sockets.
2. Install the antenna onto the SMB connector.
3. Supply the STK500 with +12 V power by connecting it to a PC using the RS232 port.
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Getting Started
2.2Initial Programming
After setting-up the hardware, insert the accompanying CD into the computer’s CDROM drive.
Note:If you want to use something other than the pre-compiled demonstration software and EEPROM files
included on the CD, there is additional programming information in Section 3, Programming Notes.
1. Apply power to the STK500 by moving the power switch toward the edge of the board.
2. If not already done, install and/or open AVR Studio.
3. When the first box appears entitled, “Welcome to AVR Studio 4,” click “Cancel” (to program the
devices doesn't require that a “Project” be used).
4. Click on the black IC icon with “AVR” -- it is in one of the top rows of the AVR Studio screen.
(Note: When hovering over this symbol with the mouse pointer, “connect to the selected AVR programmer” appears. This indicates that this is the correct icon).
A pop-up window labeled “STK500” appears.
5. AVR Studio is now ready to program the transmitter(s) and receiver.
2.2.1Programming the ATmega88 to Control the Receiver
1. Select the “Program” tab and then select ATmega88 from the pull down menu.
2. Select the “Advanced” tab and then select “read signature” to ensure that communication with the
device is functioning properly. If the read attempt is successful, a number will show in the window. If
not, a pop-up will appear describing the failure. Consult the STK500 documentation to handle any
failures.
3. Select the “Fuses” tab and ensure that the Fuses are set as shown in Table 2-1
Table 2-1. Receiver ATmega88 Fuse Settings
Fuse NameSetting
Boot Flash section size = 1024…
Brown-out detection disabled
Int RC Osc 8 MHz: … +64 ms
Divide clock by 8 internally
Watchdog Timer always on
Checked
Checked
Checked
Not Checked
Not checked
4. From the CD, in the folder “software\IAR\RX\Release\Exe,” program the flash of the ATMega88 with
“RX_fffMHz.a90.” (Note: “fff” is 315, 434, 868 or 915, the frequency specified for this kit).
5. From the CD, in the folder “software\Precompiled,” program the EEPROM of the ATMega88 with
“RX_EEPROM_AES128.hex.”
The ATMega88 is now programmed to control the receiver.
Note:About receiver programming: the two rows of DIP switches on the interface board provide the capability to
set the OPMODE and LIMIT registers of the receiver IC. These DIP switches are NOT used by this demonstration software, as the receiver is programmed by the ATmega88. More can be found about how these
switches work by consulting the appropriate Data Sheets for the receiver ICs used in this kit. To avoid accidental misprogramming of the receiver IC when using this demonstration kit, avoid pushing the white
“CONFIGURE” button when the black slide switch is in the “STK512” position!
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2.2.2Programming the Transmitter(s)
1. On the STK500, remove the 6-pin cable from the “SPROG2” header, plug it into the ISP programming adapter. Next, insert the transmitter application board into the adapter, as shown in Figure 2-6.
Figure 2-6. Transmitter Key Fob with 6-pin Cable
Getting Started
2. On the “Program” tab of the “STK500” pop-up window, select the ATtiny44 from the pull-down list.
3. In the “Advanced” tab select “read signature” to ensure that communication with the device is functioning properly. If the read attempt is successful, a number will show in the window. If not, a pop-up
will appear, describing the failure. Consult the STK500 documentation to handle any failures.
4. Select the “fuses” tab and ensure that the Fuses are set as shown in Table 2-2.
Table 2-2. Transmitter ATtiny44 Fuse Settings
Fuse NameSetting
Preserve EEPROM memory…
Brown-out detection disabled
Int RC Osc 8 MHz: … +64 ms
Divide clock by 8 internally
Watchdog Timer always on
Checked
Checked
Checked
Not Checked
Not checked
5. From the CD, in the folder “software\IAR\TX\Release\Exe,” program the flash of the ATtiny45 with
“TX.a90.”
6. From the CD, in the folder “software\Precompiled,” program the EEPROM of the Tiny45 with
“TX_EEPROM_AES128_ID1.”
7. Repeat this process for the second transmitter, except with the file “TX_EEPROM_AES128_ID2.”
The transmitters are now programmed and ready for use.
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Getting Started
2.3Teach the Transmitters to the Receiver
In order for the rolling code to work, each transmitter must convey to (teach) the receiver three data elements: its unique serial number, its secret key, and its sequence counter value. The “learn mode” is
physically activated at the receiver during which time authorized transmitters can transmit their specific
information. This teaching and learning process is accomplished by the following steps.
For security purposes, when the receiver enters the learn mode, all previous data concerning transmitters should be erased. This is discussed in further detail in section 3.2 of the “AVR411: Secure Rolling
Code Algorithm for Wireless Link Application Note” that is furnished on the CDROM. This requirement
has not been implemented in this starter kit in order to allow further investigation into this mode.
Familiarize yourself with the following instructions before beginning the teaching process.
Also, keep your transmitter key fobs readily available. The default timeout to teach a transmitter is 10
seconds before the receiver will exit the learn mode.
1. Enter learn mode on the receiver by pressing the SW5 button on the STK500. The LED marked
LED5 illuminates, indicating that the receiver is in learn mode.
2. Within 10 seconds, press Switch 1 on the transmitter key fob you want the receiver to recognize.
Inadvertently pressing any other button or combination of buttons will transmit an ordinary message
that will be ignored by the receiver since the receiver is expecting a longer “teach” message. Once
the receiver receives the “teach” message, the learn-mode LED5 blinks off once, and you have
another 10 seconds to teach the next transmitter. If LED5 does not blink, the message was not
received correctly, perhaps due to interference or an incorrect button combination. Repeat steps 1
and 2 until successful.
Figure 2-7. Transmitter Key Fob Button Numbering
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3. Repeat steps 1 and 2 for to teach additional transmitters.
4. When the last transmitter has been taught to the receiver, wait for the 10-second learn-mode timeout
to expire. At this Point, LED5 goes off and the receiver is ready to accept regular messages from the
transmitters.
Note:Whenever the maximum number of transmitters is reached, LED5 blinks to indicate that a transmitter has
been learned, but there is not another 10-second delay. LED5 goes off immediately after blinking.
2.4The Demonstration
On the STK500, LED0 through LED4 represent a sequential circular counter (i.e., LEDs 0 through 4 illuminate in sequence and then LEDs 0 through 4 again illuminate in sequence, etc.). Pressing Switch 3 on
a learned transmitter key fob increments the code counter and the illuminated LED; pressing Switch 2,
the counter and the illuminated LED de-increments.
Since the rolling code is transparent (embedded in the transmitted message) to the end user of a system, by default, the software provided in this starter kit is designed to simply demonstrate the reliable
receipt of transmissions originating from the transmitter key fobs.
A necessary component of this secure encryption algorithm is synchronization between the transmitter
and receiver. To demonstrate synchronization feature, a situation must be created to cause a transmitter
key fob’s counter to become out of sequence with the receiver’s respective counter. With the source
code provided, the window of acceptance defaults to a value of 100. That is, the transmitter key fob must
increment its counter 100 times above the count the receiver remembers for that transmitter key fob.
This can be done by moving the transmitter key fob out of range of the receiver and pressing either
Switch 2 or 3 more than 100 times. When the transmitter key fob is again brought within range of the
receiver; note that the receiver will not respond to that transmitter key fob because the counters are out
of sequence more than 100. This synchronization feature is further explained in section 3.1.1 of the
“AVR411: Secure Rolling Code Algorithm for Wireless Link Application Note” that is furnished on the
CDROM.
Getting Started
To simplify demonstrating the out-of-sync situation, the size of the “rolling window of acceptance” variable can be reduced. This reduces the number of times the transmitter key fob switches must be
pressed to cause an out of sync condition.
Similar to the above approach, incremented counter values can be changed through manipulation of the
counter value variable directly in software. Atmel recommends appropriate variable monitoring capabili
ties be available before attempting this approach.
Whichever approach is used, the transmitter key fob and receiver counter can be resynchronized by
having the receiver relearn the transmitter key fob.
-
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The following describes optional programming that is not necessary to use the kit to demonstrate the rolling code algorithm over an RF link. In addition to the information below, the accompanying CD contains
a “readme.html” file that documents user programming of both the receiver and transmitter.
This information is included for the advanced user who wishes to experiment with the kit and its
expanded capabilities.
3.1Configuration
There are numerous options for the system, e.g., cryptographic key sizes, message field sizes etc. The
parameters are given as #define macros in the config.h files in both the transmitter and receiver source
code folder. The most important parameters are given in. It is important that the parameters for the trans
mitter and receiver code are the same.
The configuration file contains several other advanced parameters. Parameter usage is explained in
comment blocks in the files themselves and should not be altered. Always keep a backup copy of the
original default configuration.
Section 3
Programming Notes
-
Table 3-1. Basic Configuration Parameters
Default
Parameter Name
KEY_BITS128
SERIAL_NO_BYTES4
COMMAND_CODE_BYTES1
SEQ_COUNTER_BYTES4
MAC BYTES - 4
MAX_TRANSMITTERS5
WINDOW SIZE -100The size of the rolling window of acceptance.
Note:1. Serial number, command code and sequential counter value fields must not exceed 16 bytes. A compile
error will occur if the total size exceeds this limit.
ValueDescription
Size of the AES cipher key in bits. Allowed values are 128, 192 and 256
bits, where 256 bits is the most secure option.
Size in bytes of the message field containing a transmitter's serial
number. Allowed values are 1, 2, and 4 bytes
Size in bytes of the message field containing the requested command.
Allowed values are 1, 2, and 4 bytes
Size in byte of the message field containing the sequential counter
value. Allowed values are 1, 2, and 4 bytes
Size in bytes of the message field containing the MAC. The value must
not be larger than 16 bytes. More bytes give a more secure
authentication.
Maximum number of transmitters that one receiver can learn. This
number is limited by the amount of free EEPROM memory. A compile
error will occur of the number is chosen too large.
(1)
.
(1)
.
(1)
.
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Programming Notes
3.2Project Compilation
This step can be skipped if you only want to use the precompiled source code with default settings. If
not, compile projects for both the transmitter and the receiver. Detailed compilation instructions and fuse
settings are giving in the source code documentation.
3.3EEPROM Image Generation
Allocate serial numbers and secret and shared keys for the system components. Then use the supplied
command line tools to generate one HEX file for every unit. The secret key for the transmitters should be
discarded after generating the HEX file. They are not needed and could compromise system security if
they get into the wrong hands.
Make sure that all transmitters that will be associated with a receiver have the same shared key as the
receiver.
Note:1. The supplied tools are only meant for prototyping and evaluation. For full production use, a secure key
management infrastructure should be established.
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Table 4-1. Troubleshooting Solutions
ProblemReasonSolution
Power is not applied or is less than 5V
LED on Receiver
Application Board
not active
LED(s) on STK512
Interface Board not
active
Registers in the
receiver do not
appear to be
programming
DATA Selector switch was not set to the STK511
position when power was applied
Receiver in permanent sleep mode because Sleep
mode of all 1s selected in OPMODE register
Receiver Application Board rotated 180° when mounted
on the STK512 Interface Board
Power not applied
Corresponding DIP Switch bit(s) not set
Bias resistor(s) damaged
Incorrect firmware loaded into the STK512 Interface
Board where I/O port of the onboard microcontroller
programmed to logic high
Power supplied is too lowVerify that the power being supplied is 5V
DATA Selector switch was not set to the STK511
position when Configure button pressed
STK512 Interface Board firmware has become
corrupted
Registers may be programming correctly with no visible
signs of change Some external source may be holding
the Data line low
Section 4
Troubleshooting Guide
Verify that 5V is supplied to the Receiver Application
Board via on-board pins or through the STK512 Interface
Board connection to the STK 500 (VTG jumper).
Set DATA Selector switch to STK511 and re-apply 5V
supply
Select different polling rate and re-program OPMODE
register
Verify that Receiver Application Board signal test points
are placed toward the DIP switches.
Verify that Power is supplied to the STK512 Interface
Board through either the Receiver Application Board or
the STK500 Board (VTG jumper).
Set the corresponding bit(s) to ON on the DIP Switch for
that register.
Replace the corresponding bias resistor(s) on the back of
the STK512 Interface Board with 1 k
Reload the STK512 Interface Board Firmware as
described in Section 2.2.
Set DATA Selector switch to STK512 and re-press button
Reload the STK512 Interface Board Firmware as
described in Section 2.2.
Monitor the Data Test point with an oscilloscope to check
for presence of the acknowledge bit.
Receiver Application Board rotated 180° when mounted
on the STK512 Interface Board
STK512 User Guide4-1
Verify that Receiver Application Board signal test points
are toward the DIP switches.
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Troubleshooting Guide
Table 4-1. Troubleshooting Solutions (Continued)
ProblemReasonSolution
STK512 Interface Board not correctly connected to
STK500
ISP ribbon cable not connected properly
Unable to load
STK512 Interface
Board firmware
Transmitter not
responding to
button press
No activity on
Tr a ns m i t te r
Application Board
LED(s)
Tr a ns m i t te r
Application Board
LED(s) constantly lit
Unable to program
Tr a ns m i t te r
Application board
through ISP header
Demo not working
(STK500 LED(s) not
responding to
transmitted signal)
Incorrect device selected
Device present in STK500 sockets
ISP jumper not shorted on STK512 Interface BoardConnect shunt
Power and serial cable not connected to STK500Verify setup of the STK500 hardware
Battery dead
Demo Software corruptedReload the desired software according to Section 2.2.
Switch contact not made
Low Battery voltageReplace coin cell battery
Transmitter is in sleep modePress button to wake from sleep mode
Demo Software corruptedReload the desired software according to Section 2.2.
Demo Software corruptedReload the desired software according to Section 2.2.
Incorrect orientation of the ribbon cable connecting the
ISP header to the STK500
Power not supplied to transmitter on-board
microcontroller
Wrong device selected in the STK500 software
Power and serial cable not connected to STK500Verify setup of the STK500 hardware
Incorrect orientations of the Receiver Application Board
or STK512 Interface Board
Power not properly supplied to all boardsSee the troubleshooting section for each board.
Data Selector switch not set to STK500 positionSet the switch to the proper position and re-run the demo
Microcontroller socket on STK500 not populated
Corrupted software in the STK500 microcontroller
10-pin ribbon cable not connected properly
Incompatible modulation used on the transmitter and
receiver
Receiver set to permanent sleepCheck for Sleep bits in the OPMODE register set for all 1s
Receiver limits incorrectVerify correct register settings as given in Section 2.
Receiver antenna not connected
Verify EXPANDO and EXPAND1 are properly oriented
Ensure ribbon cable connected between ISP6PIN header
and SPROG3 header
Check orientation of pin 1 on headers
Select ATmega8515 from the Device menu. Verify that the
signature byte matches in the Advanced tab
Remove all devices from the programming sockets of the
STK500
Open Transmitter Application Board case and replace
coin cell battery
Ensure proper contact of the button to the Transmitter
Application Board
Verify the orientation of both sides of the ribbon cable
Supply 3 volts to the transmitter microcontroller through
the coin cell battery or via the STK500
Select ATtinyl3 from the Device menu. Verify that the
signature We matches in the Advanced tab
Verify the hardware is assembled correctly as shown in
Section 2.
The demo uses an ATmega88 microcontroller in the
STK500 to decode the received signal
Reload the Receiver Decode software as shown
in Section 2.
Verify that the 10-pin ribbon cable is properly connected
to the LEDS header from the PORTC header on the
STK500
Verify that transmitter and receiver are both set for the
same modulation type (ASK versus FSK)
Connect external whip antenna to Receiver Application
Board
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