HCS301-SN [MICROCHIP]
KEELOQ CODE HOPPING ENCODER; KEELOQ跳码编码器
| 型号： | HCS301-SN |
| 厂家： | 
MICROCHIP |
| 描述： | KEELOQ CODE HOPPING ENCODER |
| 文件： | 总20页 (文件大小：170K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
HCS301
KEELOQ Code Hopping Encoder*
FEATURES
PACKAGE TYPES
Security
PDIP, SOIC
8
7
6
5
VDD
LED
PWM
VSS
S0
• Programmable 28-bit serial number
• Programmable 64-bit encryption key
• Each transmission is unique
• 66-bit transmission code length
• 32-bit hopping code
1
2
3
4
S1
S2
S3
• 34-bit fixed code (28-bit serial number,
4-bit button code, 2-bit status)
• Encryption keys are read protected
Operating
HCS301 BLOCK DIAGRAM
• 3.5V - 13.0V operation
• Four button inputs
- 15 functions available
Oscillator
Power
latching
and
Controller
Reset circuit
switching
• Selectable baud rate
LED
LED driver
• Automatic code word completion
• Battery low signal transmitted to receiver
• Battery low indication on LED
• Non-volatile synchronization data
EEPROM
Encoder
Other
PWM
• Functionally identical to HCS300
• Easy to use programming interface
• On-chip EEPROM
• On-chip oscillator and timing components
• Button inputs have internal pulldown resistors
• Current limiting on LED output
• Low external component cost
32-bit shift register
VSS
Button input port
VDD
S2
S3
S1 S0
Typical Applications
The HCS301 is ideal for Remote Keyless Entry (RKE)
applications. These applications include:
The HCS301 combines a 32-bit hopping code
generated by a non-linear encryption algorithm, with a
28-bit serial number and six status bits to create a
66-bit transmission stream. The length of the
transmission eliminates the threat of code scanning
and the code hopping mechanism makes each
transmission unique, thus rendering code capture and
resend (code grabbing) schemes useless.
• Automotive RKE systems
• Automotive alarm systems
• Automotive immobilizers
• Gate and garage door openers
• Identity tokens
• Burglar alarm systems
The encryption key, serial number, and configuration
data are stored in EEPROM which is not accessible via
any external connection. This makes the HCS301 a
very secure unit. The HCS301 provides an easy to use
serial interface for programming the necessary security
keys, system parameters, and configuration data.
DESCRIPTION
The HCS301, from Microchip Technology Inc., is a code
hopping encoder designed for secure Remote Keyless
Entry (RKE) systems. The HCS301 utilizes the KEELOQ
code hopping technology, which incorporates high secu-
rity, a small package outline, and low cost, to make this
device a perfect solution for unidirectional remote key-
less entry systems and access control systems.
The encryption keys and code combinations are pro-
grammable but read-protected. The keys can only be
verified after an automatic erase and programming
operation. This protects against attempts to gain
access to keys and manipulate synchronization values.
KeeLoq is a registered trademark of Microchip Technology Inc.
*Code hopping encoder patents issued for Europe, U. S. A., and R. S. A.
1996 Microchip Technology Inc.
Preliminary
DS21143A-page 1
HCS301
The HCS301 operates over a wide voltage range of
3.5 volts to 13.0 volts and has four button inputs in an
8-pin configuration.This allows the system designer the
freedom to utilize up to 15 functions. The only
components required for device operation are the but-
tons and RF circuitry, allowing a very low system cost.
1.1.2
SECURE LEARN*
The transmitter is activated through a special button
combination to transmit a stored 48-bit value (random
seed) that can be used for key generation or be part of
the key. Transmission of the random seed can be dis-
abled after learning is completed.
1.0
SYSTEM OVERVIEW
Most low-end keyless entry systems transmit the same
code from a transmitter every time a button is pushed.
The relative number of code combinations for a low end
system is also a relatively small number. These
shortcomings provide the means for a sophisticated
thief to create a device that ‘grabs’ a transmission and
re-transmits it later, or a device that scans all possible
combinations until the correct one is found.
Key Terms
• Manufacturer’s code – a 64-bit word, unique to
each manufacturer, used to produce a unique
encryption key in each transmitter (encoder).
• Encryption Key – a unique 64-bit key generated
and programmed into the encoder during the
manufacturing process. The encryption key
controls the encryption algorithm and is stored in
EEPROM on the encoder device.
The HCS301 employs the KEELOQ code hopping
encryption algorithm to achieve a high level of security.
Code hopping is a method by which the code
transmitted from the transmitter to the receiver is
different every time a button is pushed. This method,
coupled with a transmission length of 66 bits, virtually
eliminates the use of code ‘grabbing’ or code
‘scanning’.
1.1
Learn
The HCS product family facilitates several learn strate-
gies to be implemented on the decoder. The following
are examples of what can be done. It must be pointed
out that there exists some third-party patents on learn-
ing strategies and implementation.
As indicated in the block diagram on page one, the
HCS301 has a small EEPROM array which must be
loaded with several parameters before use. The most
important of these values are:
The HCS301 is a code hopping encoder device that is
designed specifically for keyless entry systems,
primarily for vehicles and home garage door openers. It
is meant to be a cost-effective, yet secure solution to
such systems. The encoder portion of a keyless entry
system is meant to be held by the user and operated to
gain access to a vehicle or restricted area. The
HCS301 requires very few external components
(Figure 2-1).
• A 28-bit serial number which is meant to be
unique for every encoder
• An encryption key that is generated at the time of
production
• A 16-bit synchronization value
The serial number for each transmitter is programmed
by the manufacturer at the time of production. The
generation of the encryption key is done using a key
generation algorithm (Figure 1-1). Typically, inputs to
the key generation algorithm are the serial number of
the transmitter and a 64-bit manufacturer’s code. The
manufacturer’s code is chosen by the system
manufacturer and must be carefully controlled. The
manufacturer’s code is a pivotal part of the overall
system security.
1.1.1
NORMAL LEARN
The receiver uses the same information that is transmit-
ted during normal operation to derive the transmitter’s
secret key, decrypt the discrimination value and the
synchronization counter.
FIGURE 1-1: CREATION AND STORAGE OF ENCRYPTION KEY DURING PRODUCTION
HCS301 EEPROM Array
Transmitter
Serial Number
Serial Number
Encryption Key
Sync Counter
.
.
.
Key
Encryption
Key
Manufacturer’s
Code
Generation
Algorithm
*KEELOQ learning patents pending.
DS21143A-page 2
Preliminary
1996 Microchip Technology Inc.
HCS301
The 16-bit synchronization value is the basis for the
transmitted code changing for each transmission, and
is updated each time a button is pressed. Because of
the complexity of the code hopping algorithm, a change
in one bit of the synchronization value will result in a
large change in the actual transmitted code. There is a
relationship (Figure 1-2) between the key values in
EEPROM and how they are used in the encoder. Once
the encoder detects that a button has been pressed,
the encoder reads the button and updates the synchro-
nization counter. The synchronization value is then
combined with the encryption key in the encryption
algorithm and the output is 32 bits of encrypted infor-
mation. This data will change with every button press,
hence, it is referred to as the hopping portion of the
code word. The 32-bit hopping code is combined with
the button information and the serial number to form the
code word transmitted to the receiver. The code word
format is explained in detail in Section 4.3.
Any type of controller may be used as a receiver, but it
is typically a microcontroller with compatible firmware
that allows the receiver to operate in conjunction with a
transmitter, based on the HCS301. Section 7.0
provides more detail on integrating the HCS301 into a
total system.
Before a transmitter can be used with a particular
receiver, the transmitter must be ‘learned’ by the
receiver. Upon learning a transmitter, information is
stored by the receiver so that it may track the
transmitter, including the serial number of the
transmitter, the current synchronization value for that
transmitter and the same encryption key that is used on
the transmitter. If a receiver receives a message of valid
format, the serial number is checked and, if it is from a
learned transmitter, the message is decrypted and the
decrypted synchronization counter is checked against
what is stored. If the synchronization value is verified,
then the button status is checked to see what operation
is needed. Figure 1-3 shows the relationship between
some of the values stored by the receiver and the val-
ues received from the transmitter.
FIGURE 1-2: BASIC OPERATION OF TRANSMITTER (ENCODER)
Transmitted Information
KEELOQ
Encryption
Algorithm
Button Press
Information
32 Bits of
Encrypted Data
Serial Number
EEPROM Array
Encryption Key
Sync Counter
Serial Number
FIGURE 1-3: BASIC OPERATION OF RECEIVER (DECODER)
Check for
Match
EEPROM Array
KEELOQ
Encryption
Algorithm
Decrypted
Synchronization
Counter
Encryption Key
Sync Counter
Check for
Match
Serial Number
Manufacturer Code
32 Bits of
Encrypted Data
Button Press
Information
Serial Number
Received Information
1996 Microchip Technology Inc.
Preliminary
DS21143A-page 3
HCS301
The high security level of the HCS301 is based on the pat-
ented KEELOQ technology. A block cipher based on a block
length of 32 bits and a key length of 64 bits is used. The
algorithm obscures the information in such a way that even
if the transmission information (before coding) differs by
only 1 bit from the information in the previous transmis-
sion, the next coded transmission will be totally different.
Statistically, if only 1 bit in the 32-bit string of information
changes, approximately 50 percent of the coded transmis-
sion will change.The HCS301 will wake up upon detecting
a switch closure and then delay approximately 10 ms for
switch debounce (Figure 2-2). The synchronization infor-
mation, fixed information, and switch information will be
encrypted to form the hopping code. The encrypted or
hopping code portion of the transmission will change every
time, even if the same button is pushed again. A code that
has been transmitted will not occur again for more than
64K transmissions.This will provide more than 18 years of
typical use before a code is repeated, based on 10 opera-
tions per day. Overflow information sent from the encoder
can be used by the decoder to extend the number of
unique transmissions to more than 192K.
2.0
DEVICE OPERATION
As shown in the typical application circuits (Figure 2-1),
the HCS301 is a simple device to use. It requires only
the addition of buttons and RF circuitry for use as the
transmitter in your security application. A description of
each pin is described in Table 2-1.
Note:
When VDD > 9.0V and driving low capacitive
loads, a resistor with a minimum value of 50Ω
should be used in line with VDD. This prevents
clamping of PWM at 9.0V in the event of PWM
overshoot.
FIGURE 2-1: TYPICAL CIRCUITS
+12V
(Note 2)
R
VDD
B0
B1
S0
VDD
LED
PWM
VSS
S1
S2
S3
Tx out
If, in the transmit process, it is detected that a new but-
ton(s) has been pressed, a reset will immediately be
forced and the code word will not be completed. Please
note that buttons removed will not have any effect on the
code word unless no buttons remain pressed. In this case,
the code word will be completed and the power down will
occur.
2 button remote control
+12V
(Note 2)
VDD
R
B4 B3 B2 B1 B0
FIGURE 2-2: ENCODER OPERATION
S0
VDD
LED
PWM
VSS
Power Up
(A button has been pressed)
S1
S2
S3
Tx out
Reset and Debounce Delay
(10 ms)
5 button remote control (Note1)
Sample Inputs
Note 1:
Up to 15 functions can be implemented by pressing
more than one button simultaneously or by using a
suitable diode array.
Update Sync Info
2: Resistor (R) is recommended for current limiting.
Encrypt With
Encryption Key
TABLE 2-1:
PIN DESCRIPTIONS
Description
Load Transmit Register
Transmit
Pin
Name
Number
S0
S1
S2
1
2
3
Switch input 0
Switch input 1
Yes
Buttons
Added?
Switch input 2/Can also be clock
pin when in programming mode
No
S3
4
Switch input 3/Clock pin when in
programming mode
All
No
Buttons
Released?
VSS
5
6
Ground reference connection
PWM
Pulse width modulation (PWM)
output pin/Data pin for
programming mode
Yes
Complete Code
Word Transmission
LED
VDD
7
8
Cathode connection for directly
driving LED during transmission
Stop
Positive supply voltage
connection
DS21143A-page 4
Preliminary
1996 Microchip Technology Inc.
HCS301
3.2
SYNC (Synchronization Counter)
3.0
EEPROM MEMORY
ORGANIZATION
This is the 16-bit synchronization value that is used to
create the hopping code for transmission. This value
will be changed after every transmission.
The HCS301 contains 192 bits (12 x 16-bit words) of
EEPROM memory (Table 3-1). This EEPROM array is
used to store the encryption key information,
synchronization value, etc. Further descriptions of the
memory array is given in the following sections.
3.3
SER_0, SER_1 (Encoder Serial
Number)
SER_0 and SER_1 are the lower and upper words of
the device serial number, respectively. Although there
are 32 bits allocated for the serial number, only the
lower order 28 bits are transmitted. The serial number
is meant to be unique for every transmitter. The most
significant bit of the serial number (Bit 31) is used to
turn the auto shutoff timer on or off.
TABLE 3-1:
EEPROM MEMORY MAP
WORD
ADDRESS
MNEMONIC
DESCRIPTION
0
1
2
3
4
KEY_0
64-bit encryption key
(word 0)
KEY_1
KEY_2
KEY_3
SYNC
64-bit encryption key
(word 1)
3.3.1
AUTO-SHUTOFF TIMER SELECT
64-bit encryption key
(word 2)
The most significant bit of the serial number (Bit 31) is
used to turn the Auto-shutoff timer on or off. This timer
prevents the transmitter from draining the battery
should a button get stuck in the on position for a long
period of time. The time period is approximately
25 seconds, after which the device will go to the
Time-out mode.When in the Time-out mode, the device
will stop transmitting, although since some circuits
within the device are still active, the current draw within
the Shutoff mode will be more than Standby mode. If
the most significant bit in the serial number is a one,
then the Auto-shutoff timer is enabled, and a zero in the
most significant bit will disable the timer. The length of
the timer is not selectable.
64-bit encryption key
(word 3)
16-bit synchronization
value
5
6
RESERVED Set to 0000H
SER_0 Device Serial Number
(word 0)
7
SER_1(Note) Device Serial Number
(word 1)
8
9
SEED_0
SEED_1
EN_KEY
CONFIG
Seed Value (word 0)
Seed Value (word 1)
16-bit Envelope Key
Configuration Word
3.4
SEED_0, SEED_1 (Seed Word)
10
11
This is the two-word (32 bits) seed code that will be
transmitted when all four buttons are pressed at the same
time. This allows the system designer to implement the
secure learn feature or use this fixed code word as part of
a different key generation/tracking process.
Note:
The MSB of the serial number contains a bit
used to select the auto shutoff timer.
3.1
Key_0 - Key_3 (64-Bit Encryption Key)
3.5
EN_Key (Envelope Encryption Key)
The 64-bit encryption key is used by the transmitter to
create the encrypted message transmitted to the
receiver. This key is created and programmed at the
time of production using a key generation algorithm.
The key generation algorithm is different from the
KEELOQ algorithm, although it too is a proprietary
encryption method. Inputs to the key generation
algorithm are the serial number for the particular
transmitter being used and the 64-bit manufacturer’s
code. While the key generation algorithm supplied from
Microchip is the typical method used, a user may elect
to create their own method of key generation. This may
be done providing that the decoder is programmed with
the same means of creating the key for
decryption purposes.
Envelope encryption is a selectable option that
encrypts the portion of the transmission that contains
the transmitter serial number and function code. Select-
ing this option is done by setting the appropriate bit in
the configuration word (Table 3-2). Normally, the serial
number and function code are transmitted in the clear
(unencrypted), but for an added level of security, the
system designer may elect to implement this option.
The envelope encryption key is used to encrypt the
serial number and function code portion of the trans-
mission, if the envelope encryption option has been
selected. The envelope encryption algorithm is a differ-
ent algorithm than the key generation or transmit
encryption algorithm.The EN_key is typically a random
number and the same for all transmitters in a system.
1996 Microchip Technology Inc.
Preliminary
DS21143A-page 5
HCS301
0x0000 and clear OVR1 the second time the counter
wraps. Once cleared, OVR0 and OVR1 cannot be set
again, thereby creating a permanent record of the
counter overflow. This prevents fast cycling of 64K
counter. If the decoder system is programmed to track
the overflow bits, then the effective number of unique
synchronization values can be extended to 196,608.
3.6
Configuration Word
The configuration word is a 16-bit word stored in
EEPROM array that is used by the device to store
information used during the encryption process, as well
as the status of option configurations. Further
explanations of each of the bits are described in the
following sections.
3.6.3
ENVELOPE ENCRYPTION (EENC)
TABLE 3-2:
Bit Number
CONFIGURATION WORD
Bit Description
If the EENC bit is set to a 1, the serial number and func-
tion code will also be encrypted so that it will appear to
be random.The 16-bit envelope key and envelope algo-
rithm will be used for encryption.
0
1
Discrimination Bit 0
Discrimination Bit 1
2
Discrimination Bit 2
3.6.4
BAUDRATE SELECT BITS (BSL0, BSL1)
3
Discrimination Bit 3
BSL0 and BSL1 select the speed of transmission and
the code word blanking. Table 3-3 shows how the bits
are used to select the different baud rates and
Section 5.2 provides detailed explanation in code word
blanking.
4
Discrimination Bit 4
5
Discrimination Bit 5
6
Discrimination Bit 6
7
Discrimination Bit 7
8
Discrimination Bit 8
TABLE 3-3:
BSL1 BSL0
BAUDRATE SELECT
9
Discrimination Bit 9
Basic Pulse
Element
Code Words
Transmitted
10
11
12
13
14
15
Overflow Bit 0 (OVR0)
Overflow Bit 1 (OVR1)
Low Voltage Trip Point Select
Baudrate Select Bit 0 (BSL0)
Baudrate Select Bit 1 (BSL1)
Envelope Encryption Select (EENC)
0
0
1
1
0
1
0
1
400µs
200µs
100µs
100µs
All
1 out of 2
1 out of 2
1 out of 4
3.6.1
DISCRIMINATION VALUE
(DISC0 TO DISC9)
The discrimination value can be programmed with any
value to serve as a post decryption check on the
decoder end. In a typical system, this will be
programmed with the 10 least significant bits of the
serial number or a constant value, which will also be
stored by the receiver system after a transmitter has
been learned. The discrimination bits are part of the
information that is to form the encrypted portion of the
transmission. After the receiver has decrypted a trans-
mission, the discrimination bits can be checked against
the stored value to verify that the decryption process
was valid.
3.6.2
OVERFLOW BITS (OVR0 AND OVR1)
The overflow bits are used to extend the number of pos-
sible synchronization values. The synchronization
counter is 16 bits in length, yielding 65,536 values
before the cycle repeats. Under typical use of
10 operations a day, this will provide nearly 18 years of
use before a repeated value will be used. Should the
system designer conclude that is not adequate, then
the overflow bits can be utilized to extend the number of
unique values. This can be done by programming
OVR0 and OVR1 to 1s at the time of production. The
encoder will automatically clear OVR0 the first time that
the synchronization value wraps from 0xFFFF to
DS21143A-page 6
Preliminary
1996 Microchip Technology Inc.
HCS301
3.6.5
LOW VOLTAGE TRIP POINT SELECT
4.0
TRANSMITTED WORD
The low voltage trip point select bit is used to tell the
HCS301 what VDD level is being used.This information
will be used by the device to determine when to send
the voltage low signal to the receiver. When this bit is
set to a one, the VDD level is assumed to be operating
from a 9.0 volt or 12.0 volt VDD level. If the bit is set low,
then the VDD level is assumed to be 6.0 volts. Refer to
Figure 3-1 for voltage trip point.
4.1
Transmission Format
The HCS301 transmission is made up of several parts
(Figure 4-1). Each transmission is begun with a
preamble and a header, followed by the encrypted and
then the fixed data. The actual data is 66 bits which
consists of 32 bits of encrypted data and 34 bits of fixed
data. Each transmission is followed by a guard period
before another transmission can begin. Refer to
Table 8-4 for transmission timing requirements. The
encrypted portion provides up to four billion changing
code combinations and includes the button status bits
(based on which buttons were activated) along with the
synchronization counter value and some discrimination
bits. The fixed portion is comprised of the status bits,
the function bits and the 28-bit serial number. The fixed
and encrypted sections combined increase the number
The LED current limiting resistor value also affects the
LED current:
1 (high limiting).
0 (low limiting).
• VLOW
• VLOW
=
=
VLOW is tested at 3.5V and 13.0V.
FIGURE 3-1: TYPICAL VOLTAGE TRIP
POINTS (BY
19
CHARACTERIZATION)
of combinations to 7.38 x 10 .
4.2
Synchronous Transmission Mode
Volts (V)
VLOW
Max
VLOW sel = 0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
Synchronous transmission mode can be used to clock
the code word out using an external clock.
To enter synchronous transmission mode, the program-
ming mode start-up sequence must be executed as
shown in Figure 4-3. If either S1 or S0 is set on the fall-
ing edge of S2 (or S3), the device enters synchronous
transmission mode. In this mode, it functions as a nor-
mal transmitter, with the exception that the timing of the
PWM data string is controlled externally and that 16
extra bits are transmitted at the end with he code word.
The button code will be the S0, S1 value at the falling
edge S2 or S3. The timing of the PWM data string is
controlled by supplying a clock on S2 or S3 and should
not exceed 20 KHz. The code word is the same as in
PWM mode with 16 reserved bits at the end of the
word. The reserved bits can be ignored. When in syn-
chronous transmission mode S2 or S3 should not be
toggled until all internal processing has been com-
pleted as shown in Figure 4-4.
Min
9.0
8.5
8.0
7.5
7.0
VLOW sel = 1
Max
Min
-40 -20
0
20 40 60 80 100
Temp (C)
4.3
Code Word Organization
The HCS301 transmits a 66-bit code word when a
button is pressed. The 66-bit word is constructed from
a Fixed Code portion and an Encrypted Code portion
(Figure 4-2).
The Encrypted Data is generated from 4 button bits, 2
overflow counter bits, 10 discrimination bits and the
16-bit sync value (Figure 8-5).
The Fixed Code Data is made up from two status bits,
four button bits and the 28-bit serial number. The four
button bits and the 28-bit serial number may be
encrypted with the Envelope Key if the envelope
encryption is enabled by the user.
1996 Microchip Technology Inc.
Preliminary
DS21143A-page 7
HCS301
FIGURE 4-1: CODE WORD TRANSMISSION FORMAT
LOGIC ‘0’
LOGIC ‘1’
Bit
Period
Encrypted Portion
Fixed Portion of
Transmission
TFIX
Guard
Time
TG
Header
TH
Preamble
TP
of Transmission
THOP
FIGURE 4-2: CODE WORD ORGANIZATION
Fixed Code Data
Encrypted Code Data
Discrimina-
Repeat VLOW
(1 bit) (1 bit)
Button
Status
(4 bits)
28-bit
Button
Status
(4 bits)
16-bit
Serial Number
tion bits
(12 bits)
Sync Value
66 bits
1 bit of Status
1 bit Fixed
Serial Number and
Button Status (32 bits)
32 bits of Encrypted Data
of Data
+
+
Transmitted
FIGURE 4-3: SYNCHRONOUS TRANSMISSION MODE
t = 50 ms
PWM
S2(S3)
“01,10,11”
S[1:0]
FIGURE 4-4: TRANSMISSION WORD FORMAT DURING SYNCHRONOUS TRANSMISSION MODE
Button
Code
Reserved
Padding
Serial Number
Data Word
Sync Counter
16
2
4
28
16
16
Transmission Direction
DS21143A-page 8
Preliminary
1996 Microchip Technology Inc.
HCS301
(Figure 5-1). This is a selectable feature that is
determined in conjunction with the baudrate selection
bits BSL0 and BSL1. Using the BACW allows the user
to transmit a higher amplitude transmission if the
transmission length is shorter. The FCC puts
constraints on the average power that can be
transmitted by a device, and BACW effectively prevents
continuous transmission by only allowing the transmis-
sion of every second or every fourth code word. This
reduces the average power transmitted and hence,
assists in FCC approval of a transmitter device.
5.0
SPECIAL FEATURES
5.1
Code Word Completion
Code word completion is an automatic feature that
makes sure that the entire code word is transmitted,
even if the button is released before the transmission is
complete. The HCS301 encoder powers itself up when
a button is pushed and powers itself down after the
command is finished, if the user has already released
the button. If the button is held down beyond the time
for one transmission, then multiple transmissions will
5.3
Envelope Encryption Option
result. If another button is activated during
a
transmission, the active transmission will be aborted
and the new code will be generated using the new
button information.
Envelope Encryption is a user selectable option which
is meant to offer a higher level of security for a code
hopping system. During a normal transmission with the
envelope encryption turned off, the 28-bit serial number
and function code are transmitted in the clear (unen-
crypted). If envelope encryption is selected, then the
serial number and function code are also encrypted
before transmission. The encryption for the serial num-
ber is done using a different algorithm than the trans-
mission algorithm. The envelope encryption scheme is
not nearly as complex as the KEELOQ algorithm and,
hence, not as secure. When the envelope encryption is
used, the serial number must be decrypted using the
envelope key and envelope decryption. After the serial
number is obtained, the normal decryption method can
be used to decrypt the hopping code.
5.2
Blank Alternate Code Word
Federal Communications Commission (FCC) part 15
rules specify the limits on fundamental power and
harmonics that can be transmitted. Power is calculated
on the worst case average power transmitted in a
100ms window. It is therefore advantageous to
minimize the duty cycle of the transmitted word. This
can be achieved by minimizing the duty cycle of the
individual bits and by blanking out consecutive words.
Blank Alternate Code Word (BACW) is used for
reducing the average power of
a transmission
FIGURE 5-1: BLANK ALTERNATE CODE WORD (BACW)
Amplitude
One Code Word
100ms
100ms
100ms
100ms
BACW Disabled
(All words transmitted)
A
BACW Enabled
(1 out of 2 transmitted)
2A
BACW Enabled
(1 out of 4 transmitted)
4A
Time
1996 Microchip Technology Inc.
Preliminary
DS21143A-page 9
HCS301
5.4
Secure Learn
5.6
VLOW:Voltage LOW indicator
In order to increase the level of security in a system, it is
possible for the receiver to implement what is known as
a secure learn function.This can be done by utilizing the
seed value on the HCS301 which isstored in EEPROM
and can only be transmitted when all four button inputs
are pressed at the same time (Table 5-1). Instead of the
normal key generation method being used to create the
encryption key, this seed value is used.
The VLOW bit is transmitted with every transmission
(Figure 8-5) and will be transmitted as a one if the
operating voltage has dropped below the low voltage
trip point. The trip point is selectable between two
values, based on the battery voltage being used. See
Section 3.6.5 for a description of how the low voltage
select option is set. This VLOW signal is transmitted so
the receiver can alert the user that the transmitter bat-
tery is low.
TABLE 5-1:
PIN ACTIVATION TABLE
5.7
RPT: Repeat indicator
S3
S2
S1
S0
Notes
This bit will be low for the first transmitted word. If a
button is held down for more than one transmitted code
word, this bit will be set to indicate a repeated code
word and remain set until the button is released.
1
2
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
0
0
0
0
0
0
1
1
1
1
1
1
1
1
3
4
5.8
LED Output Operation
5
During normal transmission the LED output is LOW. If
the supply voltage drops below the low voltage trip
point, the LED output will be toggled at approximately
5 Hz during the transmission (Section 3.6.5). The limit-
ing resistor is selectable between two nominal values
(Section 3.6.5).
6
7
8
9
10
11
12
13
14
15
Note 1: Transmit generated 32-bit code hopping
word.
2: Transmit 32-bit seed value.
5.5
Auto-shutoff
The Auto-shutoff function automatically stops the
device from transmitting if a button inadvertently gets
pressed for a long period of time. This will prevent the
device from draining the battery if a button gets pressed
while the transmitter is in a pocket or purse. This func-
tion can be enabled or disabled and is selected by set-
ting or clearing the Auto-shutoff bit (Section 3.3.1).
Setting this bit high will enable the function (turn
Auto-shutoff function on) and setting the bit low will dis-
able the function. Time-out period is approximately 25
seconds.
DS21143A-page 10
Preliminary
1996 Microchip Technology Inc.
HCS301
as the data in line. After each 16-bit word is loaded, a
programming delay is required for the internal program
cycle to complete. This delay can take up to Twc. At the
end of the programming cycle, the device can be veri-
fied (Figure 6-2) by reading back the EEPROM. Read-
ing is done by clocking the S3 line and reading the data
bits on PWM. For security reasons, it is not possible to
execute a verify function without first programming the
EEPROM. A verify operation can only be done
immediately following the program cycle.
6.0
PROGRAMMING THE HCS301
When using the HCS301 in a system, the user will have
to program some parameters into the device including
the serial number and the secret key before it can be
used. The programming cycle allows the user to input
all 192 bits in a serial data stream, which are then
stored internally in EEPROM. Programming will be
initiated by forcing the PWM line high, after the S3 line
has been held high for the appropriate length of time
line (Table 6-1 and Figure 6-1). After the program mode
is entered, a delay must be provided to the device for
the automatic bulk write cycle to complete. This will
write all locations in the EEPROM to an all zeros pat-
tern. The device can then be programmed by clocking
in 16 bits at a time, using S3 as the clock line and PWM
Note: To ensure that the device does not acci-
dentally enter programming mode (result-
ing in a bulk erase), PWM should never be
pulled high by the circuit connected to it.
Special care should be taken when driving
PNP RF transistors.
FIGURE 6-1: PROGRAMMING WAVEFORMS
Enter Program
TPBW
Mode
TDS
TCLKH
TWC
S3
(Clock)
TPS
TPH1
TDH
TCLKL
PWM
(Data)
Bit 0
Bit 1
Bit 2
Bit 3
Bit 14 Bit 15
Bit 16 Bit 17
Data for Word 1
Data for Word 0 (KEY_0)
Repeat 12 times for each word
TPH2
Note 1: Unused button inputs to be held ground during the entire programming sequence.
2: The VDD pin must be taken to ground after a programming/verify cycle.
FIGURE 6-2: VERIFY WAVEFORMS
Begin Verify Cycle Here
End of
Programming Cycle
Data in Word 0
PWM
(Data)
Bit190 Bit191
Bit 0
Bit 1 Bit 2 Bit 3
Bit 14
Bit 15
Bit 16 Bit 17
Bit190 Bit191
TWC
TDV
S3
(Clock)
Note: If a verify operation is to be done, then it must immediately follow the program cycle.
TABLE 6-1:
PROGRAMMING/VERIFY TIMING REQUIREMENTS
VDD = 5.0V ± 10%
25° C ± 5 °C
Parameter
Symbol
Min.
Max.
Units
Program mode setup time
Hold time 1
Hold time 2
Bulk Write time
Program delay time
Program cycle time
Clock low time
Clock high time
Data setup time
Data hold time
TPS
TPH1
TPH2
TPBW
TPROG
TWC
TCLKL
TCLKH
TDS
3.5
3.5
50
—
—
—
25
25
0
4.5
—
—
2.2
2.2
36
—
—
—
—
24
ms
ms
µs
ms
ms
ms
µs
µs
µs
µs
µs
TDH
TDV
18
10
Data out valid time
1996 Microchip Technology Inc.
Preliminary
DS21143A-page 11
HCS301
FIGURE 7-1: TYPICAL LEARN SEQUENCE
7.0
INTEGRATING THE HCS301
INTO A SYSTEM
Enter Learn
Mode
Use of the HCS301 in a system requires a compatible
decoder.This decoder is typically a microcontroller with
compatible firmware. Microchip will provide (via a
license agreement) firmware routines that accept
transmissions from the HCS301 and decrypt the
hopping code portion of the data stream. These
routines provide system designers the means to
develop their own decoding system.
Wait for Reception
of a Valid Code
Generate Key
from Serial Number
Use Generated Key
to Decrypt
7.1
Learning a transmitter to a receiver
Compare Discrimination
Value with Fixed Value
In order for a transmitter to be used with a decoder, the
transmitter must first be ‘learned’. Several learning
strategies can be followed in the decoder implementa-
tion. When a transmitter is learned to a decoder, it is
suggested that the decoder stores the serial number
and current synchronization value in EEPROM. The
decoder must keep track of these values for every
transmitter that is learned (Figure 7-1). The maximum
number of transmitters that can be learned is only a
function of how much EEPROM memory storage is
available. The decoder must also store the manufac-
turer’s code in order to learn a transmission transmitter,
although this value will not change in a typical system
so it is usually stored as part of the microcontroller
ROM code. Storing the manufacturer’s code as part of
the ROM code is also better for security reasons.
No
Equal
?
Yes
Wait for Reception
of Second Valid Code
Use Generated Key
to Decrypt
Compare Discrimination
Value with Fixed Value
No
It must be stated that some learning strategies have
been patented and care must be taken not to infringe.
Equal
?
Yes
No
Counters
Sequential
?
Yes
Learn
Unsuccessful
Learn successful Store:
Serial number
Encryption key
Synchronization counter
Exit
DS21143A-page 12
Preliminary
1996 Microchip Technology Inc.
HCS301
7.2
Decoder operation
7.3
Synchronization with Decoder
In a typical decoder operation (Figure 7-2), the key gen-
eration on the decoder side is done by taking the serial
number from a transmission and combining that with
the manufacturer’s code to create the same secret key
that was used by the transmitter. Once the secret key is
obtained, the rest of the transmission can be decrypted.
The decoder waits for a transmission and immediately
can check the serial number to determine if it is a
learned transmitter. If it is, it takes the encrypted portion
of the transmission and decrypts it using the stored key.
It uses the discrimination bits to determine if the
decryption was valid. If everything up to this point is
valid, the synchronization value is evaluated.
The KEELOQ technology features a sophisticated
synchronization technique (Figure 7-3) which does not
require the calculation and storage of future codes. If
the stored counter value for that particular transmitter
and the counter value that was just decrypted are within
a formatted window of say 16, the counter is stored and
the command is executed. If the counter value was not
within the single operation window, but is within the
double operation window of say 32K window, the trans-
mitted synchronization value is stored in temporary
location and it goes back to waiting for another trans-
mission. When the next valid transmission is received,
it will check the new value with the one in temporary
storage. If the two values are sequential, it is assumed
that the counter had just gotten out of the single opera-
tion ‘window’, but is now back in sync, so the new syn-
chronization value is stored and the command
executed. If a transmitter has somehow gotten out of
the double operation window, the transmitter will not
work and must be re-learned. Since the entire window
rotates after each valid transmission, codes that have
been used are part of the ‘blocked’ (32K) codes and are
no longer valid. This eliminates the possibility of grab-
bing a previous code and re-transmitting to gain entry.
FIGURE 7-2: TYPICAL DECODER
OPERATION
Start
No
Transmission
Received
?
Yes
Note: The synchronization method described in
this section is only a typical implementation
and because it is usually implemented in
firmware, it can be altered to fit the needs
of a particular system
Does
Serial Number
Match
No
?
Yes
Decrypt Transmission
FIGURE 7-3: SYNCHRONIZATION WINDOW
Entire Window
rotates to eliminate
use of previously
used codes
Is
No
Decryption
Valid
?
Blocked 32K
Codes
Yes
Current
Position
Execute
Command
and
Update
Counter
Is
Counter
Within 16
?
Yes
No
No
Open 32K
Codes
No
Current window
of 16 codes
Is
Counter
Within 32K
?
Yes
Save Counter
in Temp Location
1996 Microchip Technology Inc.
Preliminary
DS21143A-page 13
HCS301
8.0
ELECTRICAL CHARACTERISTICS
TABLE 8-1:
ABSOLUTE MAXIMUM RATINGS
Symbol
Item
Rating
Units
VDD
VIN
Supply voltage
Input voltage
-0.3 to 13.3
-0.3 to 13.3
-0.3 to VDD + 0.3
25
V
V
V
VOUT
IOUT
Output voltage
Max output current
Storage temperature
Lead soldering temp
ESD rating
mA
TSTG
TLSOL
VESD
-55 to +125
300
°C (Note)
°C (Note)
V
4000
Note:
Stresses above those listed under “ABSOLUTE MAXIMUM RATINGS” may cause permanent damage to the
device.
TABLE 8-2:
DC CHARACTERISTICS
Commercial (C): Tamb = 0°C to +70°C
Industrial
(I): Tamb = -40°C to +85°C
3.5V < VDD < 13.0V
Parameter
Sym.
Min
Typ*
Max
Unit
Conditions
Operating current (avg)
ICC
0.6
1.5
8.0
1.0
3.0
12.0
VDD = 3.5V
VDD = 6.6V
VDD = 13.0V
(Figure 8-1)
mA
Standby current
ICCS
VIH
1
10
µA
High level Input voltage
0.4 VDD
VDD+
0.3
V
Low level input voltage
High level output voltage
Low level output voltage
LED sink current
VIL
-0.3
0.15 VDD
V
V
VOH
VOL
ILED
0.5VDD
IOH = -2 mA
IOL = 2 mA
0.08 VDD
V
3.5
2.7
4.7
3.7
5.9
4.6
mA
VDD = 6.6V, Vlow source = 0
VDD = 13.0V, Vlow source = 1
Resistance; S0-S3
Resistance; PWM
RS0-3
RPWM
40
80
60
80
KΩ
KΩ
VIN = 4.0V
VIN = 4.0V
120
160
*
Typical values are at 25°C.
DS21143A-page 14
Preliminary
1996 Microchip Technology Inc.
HCS301
FIGURE 8-1: TYPICAL ICC CURVE OF HCS301 WITH EXTERNAL RESISTORS
50Ω External
12.0
10.0
8.0
6.0
4.0
2.0
0.0
13
2
3
4
5
6
7
8
9
10
11
12
VBAT [V]
1K External
12.0
10.0
8.0
6.0
4.0
2.0
0.0
2
3
4
5
6
7
8
9
10
11
12
13
VBAT [V]
2K External
12.0
10.0
8.0
6.0
4.0
2.0
0.0
2
3
4
5
6
7
8
9
10
11
12
13
VBAT [V]
LEGEND
Typical
Maximum
Minimum
1996 Microchip Technology Inc.
Preliminary
DS21143A-page 15
HCS301
FIGURE 8-2: POWER UP AND TRANSMIT TIMING
Button Press
Detect
Code Word Transmission
TBP
TTD
TDB
Code
Word
n
Code
Code
Word
3
Code
Word
2
Word
PWM
1
TTO
Sn
TABLE 8-3:
POWER UP AND TRANSMIT TIMING REQUIREMENTS
VDD = +3.5 to13.0V
Commercial (C): Tamb = 0°C to +70°C
Industrial
(I): Tamb = -40°C to +85°C
Parameter
Symbol
Min
Max
Unit
Remarks
Time to second button press
TBP
10 + Code 25 + Code
Word Time Word Time
ms
(Note 1)
Transmit delay from button detect
Debounce delay
TTD
TDB
TTO
10
6
25
15
40
ms
ms
s
Auto-shutoff time-out period
20
(Note 2)
Note 1: TBP is the time in which a second button can be pressed without completion of the first code word and the
intention was to press the combination of buttons.
2: The auto shutoff timeout period is not tested.
FIGURE 8-3: PWM FORMAT
TE TE
TE
LOGIC ‘0’
LOGIC ‘1’
TBP
Encrypted Portion
of Transmission
Fixed portion of
Transmission
TFIX
Guard
Time
TG
Header
TH
Preamble
TP
THOP
FIGURE 8-4: PREAMBLE/HEADER FORMAT
Data Word
Transmission
Preamble
P0
Header
P12
Bit 0 Bit 1
10 TE
23 TE
DS21143A-page 16
Preliminary
1996 Microchip Technology Inc.
HCS301
FIGURE 8-5: DATA WORD FORMAT
Serial Number
Button Code
Status
LSB
MSB LSB
MSB S3
S0 S1 S2 VLOW RPT
Bit 0 Bit 1
Bit 30 Bit 31 Bit 32 Bit 33 Bit 58 Bit 59 Bit 60
Bit 62 Bit 63 Bit 64 Bit 65
Bit 61
Guard
Time
Fixed Code Word
Header
Hopping Code Word
TABLE 8-4:
CODE WORD TRANSMISSION TIMING REQUIREMENTS
VDD = +3.5 to 13.0
Commercial (C): Tamb = 0°C to +70°C
Code Words Transmitted
1 out of 2
All
1 out of 4
Industrial
(I): Tamb = -40°C to +85°C
Number
Characteristic
of TE
Symbol
Min. Typ. Max. Min. Typ. Max. Min. Typ. Max. Units
TE
TBP
TP
Basic pulse element
PWM bit pulse width
Preamble duration
Header duration
1
3
280
400
620
140
200
600
4.6
2.0
310
930
7.1
3.1
70
210
1.6
0.7
6.7
7.1
2.7
100
300
2.3
1.0
9.6
155
465
3.6
µs
840 1200 1860 420
µs
23
10
96
102
39
270
—
6.4
2.8
9.2
4.0
14.3
6.2
3.2
1.4
ms
ms
ms
ms
ms
ms
TH
1.6
THOP Hopping code duration
26.9 38.4 59.5 13.4 19.2 29.8
28.6 40.8 63.2 14.3 20.4 31.6
14.9
TFIX
TG
Fixed code duration
Guard Time
10.2 15.8
3.9 6.0
10.9 15.6 24.2
5.5
7.8
12.1
—
Total Transmit Time
PWM data rate
75.6 108.0 167.4 37.8 54.0 83.7 18.9 27.0 41.9
1190 833
—
538 2381 1667 1075 4762 3333 2151 bps
Note:
The timing parameters are not tested but derived from the oscillator clock.
FIGURE 8-6: HCS301 TE VS.TEMP (BY CHARACTERIZATION ONLY)
1.7
1.6
1.5
TE Max.
VDD = 3.5V
1.4
1.3
1.2
VDD ≥ 5.0V
TE Max.
TE
1.1
VDD = 5.0V
Typical
1.0
0.9
0.8
0.7
0.6
VDD ≥ 5.0V
TE Min.
-50 -40 -30 -20 -10
0
10 20 30 40 50 60 70 80 90
TEMPERATURE
1996 Microchip Technology Inc.
Preliminary
DS21143A-page 17
HCS301
NOTES:
DS21143A-page 18
Preliminary
1996 Microchip Technology Inc.
HCS301
NOTES:
1996 Microchip Technology Inc.
Preliminary
DS21143A-page 19
HCS301
HCS301 Product Identification System
To order or to obtain information (e.g., on pricing or delivery), please use the listed part numbers, and refer to the factory or the listed
sales offices.
HCS301
-
/P
Package:
P = Plastic DIP (300 mil Body), 8-lead
SN = Plastic SOIC (150 mil Body), 8-lead
Temperature
Range:
Blank = 0°C to +70°C
I = -40°C to +85°C
Device:
Code Hopping Encoder
HCS301
Code Hopping Encoder (Tape and Reel)
HCS301T
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All rights reserved.
1996, Microchip Technology Inc.,USA., 6/96
Information contained in this publication regarding device applications and the like is intended through suggestion only and may be superseded by updates. No repre-
sentation or warranty is given and no liability is assumed by Microchip Technology Incorporated with respect to the accuracy or use of such information, or infringement
of patents or other intellectual property rights arising from such use or otherwise. Use of Microchip’s products as critical components in life support systems is not autho-
rized except with express written approval by Microchip. No licenses are conveyed, implicitly or otherwise, under any intellectual property rights.The Microchip logo and
name are registered trademarks of Microchip Technology Inc. All rights reserved. All other trademarks mentioned herein are the property of their respective companies.
DS21143A-page 20
Preliminary
1996 Microchip Technology Inc.
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