HCS300-IP Microchip Technology, HCS300-IP Datasheet - Page 6

• Manufacturer Part Number: HCS300-IP
• Description: KEE LOQ Code Hopping Encoder
• Manufacturer: Microchip Technology

HCS300
3.2
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.
3.3
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.
3.3.1
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.
3.4
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 or purely as a
fixed code transmission.
3.5
Envelope encryption is a selectable option that
encrypts the portion of the transmission that contains
the transmitter serial number. Selecting this option is
done by setting the appropriate bit in the configuration
word (Table 3-2). Normally, the serial number is
transmitted in the clear (un-encrypted), 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 portion of the
transmission, if the envelope encryption option has
been selected. The envelope encryption algorithm is a
different 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.
DS21137D-page 6
SYNC (Synchronization Counter)
SER_0, SER_1 (Encoder Serial
Number)
AUTO SHUTOFF TIMER SELECT
SEED_0, SEED_1 (Seed Word)
EN_Key (Envelope Encryption Key)
Preliminary
3.6
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.
TABLE 3-2:
3.6.1
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, 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 transmission, the
discrimination bits can be checked against the stored
value to verify that the decryption process was valid.
3.6.2
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
0x0000 and clear OVR1 the second time the counter
wraps. Once cleared, OVR0 and OVR1 cannot be set
Bit Number
10
11
12
13
14
15
0
1
2
3
4
5
6
7
8
9
Configuration Word
DISCRIMINATION VALUE
(DISC0 TO DISC9)
OVERFLOW BITS (OVR0 AND OVR1)
Discrimination Bit 0
Discrimination Bit 1
Discrimination Bit 2
Discrimination Bit 3
Discrimination Bit 4
Discrimination Bit 5
Discrimination Bit 6
Discrimination Bit 7
Discrimination Bit 8
Discrimination Bit 9
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)
CONFIGURATION WORD
1996 Microchip Technology Inc.
Bit Description