HCS362
K
EE
L
OQ
®
Code Hopping Encoder
FEATURES
Security
Programmable 28/32-bit serial number
Two programmable 64-bit encryption keys
Programmable 60-bit seed
Each transmission is unique
69-bit transmission code length
32-bit hopping code
37-bit fixed code (28/32-bit serial number,
4/0-bit function code, 1-bit status, 2-bit CRC/time,
2-bit queue)
• Encryption keys are read protected
•
•
•
•
•
•
•
PACKAGE TYPES
PDIP, SOIC
S0
S1
S2
S3/RFEN
1
HCS362
2
3
4
8
7
6
5
V
DD
LED/SHIFT
DATA
V
SS
TSSOP
Operation
•
•
•
•
•
•
2.0V – 6.3V operation
Four button inputs
15 functions available
Selectable baud rates and code word blanking
Programmable minimum code word completion
Battery low signal transmitted to receiver with
programmable threshold
• Non-volatile synchronization data
• PWM and Manchester modulation
S2
S3/RFEN
V
SS
DATA
1
2
3
4
8
7
6
5
S1
S0
V
DD
LED/SHIFT
HCS362 BLOCK DIAGRAM
Oscillator
RESET Circuit
LED
RFEN
LED Driver
PLL Driver
Controller
Power
Latching
and
Switching
HCS362
Other
•
•
•
•
•
•
•
RF Enable output – PLL interface
Easy to use programming interface
On-chip EEPROM
On-chip tunable oscillator and timing components
Button inputs have internal pull-down resistors
Current limiting on LED output
Minimum component count
DATA
EEPROM
Encoder
32-bit Shift Register
SHIFT
V
SS
V
DD
Button Input Port
S3 S2 S1 S0
Enhanced Features Over HCS300
•
•
•
•
•
•
•
•
60-bit seed vs. 32-bit seed
2-bit CRC for error detection
28/32-bit serial number select
Tunable oscillator (+
−
/
10% over specified voltage
ranges)
Time bits option
Queue bits
TSSOP package
Programmable Time-out and Guard Time
Typical Applications
The HCS362 is ideal for Remote Keyless Entry (RKE)
applications. These applications include:
•
•
•
•
•
•
Automotive RKE systems
Automotive alarm systems
Automotive immobilizers
Gate and garage door openers
Identity tokens
Burglar alarm systems
©
2011 Microchip Technology Inc.
DS40189E-page 1
HCS362
GENERAL DESCRIPTION
The HCS362 is a code hopping encoder designed for
secure Remote Keyless Entry (RKE) systems. The
HCS362 utilizes the K
EE
L
OQ
®
code hopping technol-
ogy, which incorporates high security, a small package
outline and low cost, to make this device a perfect
solution for unidirectional remote keyless entry sys-
tems and access control systems.
The HCS362 combines a 32-bit hopping code
generated by a nonlinear encryption algorithm, with a
28/32-bit serial number and 9/5 status bits to create a
69-bit transmission stream. The length of the transmis-
sion eliminates the threat of code scanning. The code
hopping mechanism makes each transmission unique,
thus rendering code capture and resend (code grab-
bing) schemes useless.
The crypt key, serial number and configuration data are
stored in an EEPROM array which is not accessible via
any external connection. The EEPROM data is pro-
grammable but read protected. The data can be veri-
fied only after an automatic erase and programming
operation. This protects against attempts to gain
access to keys or manipulate synchronization values.
The HCS362 provides an easy to use serial interface
for programming the necessary keys, system parame-
ters and configuration data.
•
Decoder
- A device that decodes data received
from an encoder.
•
Decryption algorithm
- A recipe whereby data
scrambled by an encryption algorithm can be
unscrambled using the same crypt key.
•
Learn
– Learning involves the receiver calculating
the transmitter’s appropriate crypt key, decrypting
the received hopping code and storing the serial
number, synchronization counter value and crypt
key in EEPROM. The K
EE
L
OQ
product family facil-
itates several learning strategies to be imple-
mented on the decoder. The following are
examples of what can be done.
-
Simple Learning
The receiver uses a fixed crypt key, common
to all components of all systems by the same
manufacturer, to decrypt the received code
word’s encrypted portion.
-
Normal Learning
The receiver uses information transmitted
during normal operation to derive the crypt
key and decrypt the received code word’s
encrypted portion.
-
Secure Learn
The transmitter is activated through a special
button combination to transmit a stored 60-bit
seed value used to generate the transmitter’s
crypt key. The receiver uses this seed value
to derive the same crypt key and decrypt the
received code word’s encrypted portion.
•
Manufacturer’s code
– A unique and secret 64-
bit number used to generate unique encoder crypt
keys. Each encoder is programmed with a crypt
key that is a function of the manufacturer’s code.
Each decoder is programmed with the manufac-
turer code itself.
The HCS362 code hopping encoder is designed specif-
ically for keyless entry systems; primarily vehicles and
home garage door openers. The encoder portion of a
keyless entry system is integrated into a transmitter,
carried by the user and operated to gain access to a
vehicle or restricted area. The HCS362 is meant to be
a cost-effective yet secure solution to such systems,
requiring very few external components (Figure 2-1).
Most low-end keyless entry transmitters are given a
fixed identification code that is transmitted every time a
button is pushed. The number of unique identification
codes in a low-end system is usually a relatively small
number. These shortcomings provide an opportunity
for a sophisticated thief to create a device that ‘grabs’
a transmission and retransmits it later, or a device that
quickly ‘scans’ all possible identification codes until the
correct one is found.
The HCS362, on the other hand, employs the K
EE
L
OQ
code hopping technology coupled with a transmission
length of 66 bits to virtually eliminate the use of code
‘grabbing’ or code ‘scanning’. The high security level of
1.0
SYSTEM OVERVIEW
Key Terms
The following is a list of key terms used throughout this
data sheet. For additional information on K
EE
L
OQ
and
Code Hopping, refer to Technical Brief 3 (TB003).
•
RKE
- Remote Keyless Entry
•
Button Status
- Indicates what button input(s)
activated the transmission. Encompasses the 4
button status bits S3, S2, S1 and S0 (Figure 3-2).
•
Code Hopping
- A method by which a code,
viewed externally to the system, appears to
change unpredictably each time it is transmitted.
•
Code word
- A block of data that is repeatedly
transmitted upon button activation (Figure 3-2).
•
Transmission
- A data stream consisting of
repeating code words (Figure 8-1).
•
Crypt key
- A unique and secret 64-bit number
used to encrypt and decrypt data. In a symmetri-
cal block cipher such as the K
EE
L
OQ
algorithm,
the encryption and decryption keys are equal and
will therefore be referred to generally as the crypt
key.
•
Encoder
- A device that generates and encodes
data.
•
Encryption Algorithm
- A recipe whereby data is
scrambled using a crypt key. The data can only be
interpreted by the respective decryption algorithm
using the same crypt key.
DS40189E-page 2
©
2011 Microchip Technology Inc.
HCS362
the HCS362 is based on the patented K
EE
L
OQ
technol-
ogy. 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
one bit from that of the previous transmission, the next
coded transmission will be completely different. Statis-
tically, if only one bit in the 32-bit string of information
changes, greater than 50 percent of the coded trans-
mission bits will change.
As indicated in the block diagram on page one, the
HCS362 has a small EEPROM array which must be
loaded with several parameters before use; most often
programmed by the manufacturer at the time of produc-
tion. The most important of these are:
• A 28-bit serial number, typically unique for every
encoder
• A crypt key
• An initial 16-bit synchronization value
• A 16-bit configuration value
The crypt key generation typically inputs the transmitter
serial number and 64-bit manufacturer’s code into the
key generation algorithm (Figure 1-1). The manufac-
turer’s code is chosen by the system manufacturer and
must be carefully controlled as it is a pivotal part of the
overall system security.
FIGURE 1-1:
Production
Programmer
CREATION AND STORAGE OF CRYPT KEY DURING PRODUCTION
HCS362
EEPROM Array
Serial Number
Crypt Key
Sync Counter
Transmitter
Serial Number
Manufacturer’s
Code
Key
Generation
Algorithm
Crypt
Key
.
.
.
The 16-bit synchronization counter is the basis behind
the transmitted code word changing for each transmis-
sion; it increments each time a button is pressed. Due
to the code hopping algorithm’s complexity, each incre-
ment of the synchronization value results in greater
than 50% of the bits changing in the transmitted code
word.
Figure 1-2 shows how the key values in EEPROM are
used in the encoder. Once the encoder detects a button
press, it reads the button inputs and updates the syn-
chronization counter. The synchronization counter and
crypt key are input to the encryption algorithm and the
output is 32 bits of encrypted information. This data will
change with every button press, its value appearing
externally to ‘randomly hop around’, 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 serial number to form the code word transmitted to
the receiver. The code word format is explained in
greater detail in Section 3.1.
A receiver may use any type of controller as a decoder,
but it is typically a microcontroller with compatible firm-
ware that allows the decoder to operate in conjunction
with an HCS362 based transmitter. Section 6.0
provides detail on integrating the HCS362 into a sys-
tem.
A transmitter must first be ‘learned’ by the receiver
before its use is allowed in the system. Learning
includes calculating the transmitter’s appropriate crypt
key, decrypting the received hopping code and storing
the serial number, synchronization counter value and
crypt key in EEPROM.
In normal operation, each received message of valid
format is evaluated. The serial number is used to deter-
mine if it is from a learned transmitter. If from a learned
transmitter, the message is decrypted and the synchro-
nization counter is verified. Finally, the button status is
checked to see what operation is requested. Figure 1-3
shows the relationship between some of the values
stored by the receiver and the values received from
the transmitter.
©
2011 Microchip Technology Inc.
DS40189E-page 3
HCS362
FIGURE 1-2:
EEPROM Array
Crypt Key
Sync Counter
Serial Number
BUILDING THE TRANSMITTED CODE WORD (ENCODER)
K
EE
L
OQ®
Encryption
Algorithm
Button Press
Information
Serial Number
32 Bits
Encrypted Data
Transmitted Information
FIGURE 1-3:
BASIC OPERATION OF RECEIVER (DECODER)
1 Received Information
EEPROM Array
Button Press
Information
Serial Number
32 Bits of
Encrypted Data
Manufacturer Code
2
Check for
Match
Serial Number
Sync Counter
Crypt Key
3
K
EE
L
OQ®
Decryption
Algorithm
Decrypted
Synchronization
Counter
Perform Function
5 Indicated by
button press
4
Check for
Match
NOTE:
Circled numbers indicate the order of execution.
DS40189E-page 4
©
2011 Microchip Technology Inc.
HCS362
2.0
DEVICE DESCRIPTION
FIGURE 2-1:
V
DD
TYPICAL CIRCUITS
As shown in the typical application circuits (Figure 2-1),
the HCS362 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. See Table 2-1
for a description of each pin and Figure 2-1 for typical
circuits. Figure 2-2 shows the device I/O circuits.
B0
B1
S0
S1
S2
S3
V
DD
LED
DATA
V
SS
Tx out
TABLE 2-1:
Pin
Name
Number
S0
S1
S2
S3/
RFEN
V
SS
DATA
LED/
SHIFT
V
DD
1
2
3
4
5
6
7
8
PIN DESCRIPTIONS
Description
Switch input 0
Switch input 1
Switch input 2 / Clock pin when in
Programming mode
Switch input 3 / RF enable output
Ground reference connection
Data output pin / DATA I/O pin for
Programming mode
Cathode connection for LED and
DUAL mode SHIFT input
Positive supply voltage
a) Two button remote control
V
DD
B0
B1
B2
B3
S0
S1
S2
S3
V
DD
LED
DATA
V
SS
Tx out
b) Four button remote control
with PLL output
(Note)
Note:
Up to 15 functions can be implemented by
pressing more than one button simultane-
ously or by using a suitable diode array.
V
DD
B3 B2 B1 B0
S0
S1
S2
RFEN
V
DD
LED
DATA
V
SS
PLL control
Tx out
c) Four button remote control with RF Enable
V
DD
B3 B2 B1 B0
S0
S1
S2
S3
V
DD
LED/SHIFT
DATA
V
SS
Tx out
1 KW
SHIFT
d) DUAL key, four buttons remote control
©
2011 Microchip Technology Inc.
DS40189E-page 5
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