HCS200SN Datasheet, PDF (6/34 Pages) Microchip Technology – KEELOQ Code Hopping Encoder

HCS200
3.0 EEPROM MEMORY
ORGANIZATION
The HCS200 contains 192 bits (12 x 16-bit words) of
EEPROM memory (Table 3-1). This EEPROM array is
used to store the crypt key information, synchronization
value, etc. Further descriptions of the memory array is
given in the following sections.
TABLE 3-1: EEPROM MEMORY MAP
WORD
ADDRESS
0
1
2
3
4
5
6
7
8
9
10
11
MNEMONIC
DESCRIPTION
KEY_0
KEY_1
KEY_2
KEY_3
SYNC
Reserved
SER_0
SER_1
SEED_0
SEED_1
Reserved
CONFIG
64-bit crypt key
(word 0) LSb’s
64-bit crypt key
(word 1)
64-bit crypt key
(word 2)
64-bit crypt key
(word 3) MSb’s
16-bit synchronization
value
Set to 0000H
Device Serial Number
(word 0) LSb’s
Device Serial Number
(word 1) MSb’s
Seed Value (word 0)
Seed Value (word 1)
Set to 0000H
Configuration Word
3.1 Key_0 - Key_3 (64-Bit Crypt Key)
The 64-bit crypt key is used to create the encrypted
message transmitted to the receiver. This key is calcu-
lated and programmed during production using a key
generation algorithm. The key generation algorithm
may be different from the KEELOQ algorithm. Inputs to
the key generation algorithm are typically the transmit-
ter’s serial number 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.
3.2 SYNC (Synchronization Counter)
This is the 16-bit synchronization value that is used to
create the hopping code for transmission. This value
will increment after every transmission.
3.3 Reserved
Must be initialized to 0000H.
3.4 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.
3.5 SEED_0, SEED_1 (Seed Word)
The 2-word (32-bit) seed code will be transmitted when
all three buttons are pressed at the same time (see
Figure 4-2). This allows the system designer to imple-
ment the secure learn feature or use this fixed code
word as part of a different key generation/tracking pro-
cess.
3.6 Configuration Word
The 16-bit Configuration Word stored in the EEPROM
array contains information required to form the
encrypted portion of the transmission, as well as the
device option configurations. The following sections
further explain these bits.
TABLE 3-2: CONFIGURATION WORD
Bit Number
Bit Description
0
Discrimination Bit 0
1
Discrimination Bit 1
2
Discrimination Bit 2
3
Discrimination Bit 3
4
Discrimination Bit 4
5
Discrimination Bit 5
6
Discrimination Bit 6
7
Discrimination Bit 7
8
Discrimination Bit 8
9
Discrimination Bit 9
10
Discrimination Bit 10
11
Discrimination Bit 11
12
Low Voltage Trip Point Select (VLOW
SEL)
13
Baudrate Select Bit 0 (BSL0)
14
Reserved, set to 0
15
Reserved, set to 0
3.6.1
DISCRIMINATION VALUE
(DISC0 TO DISC11)
The discrimination value aids the post-decryption
check on the decoder end. It may be any value, but in
a typical system it will be programmed as the 12 Least
Significant bits of the serial number. Values other than
this must be separately stored by the receiver when a
transmitter is learned. The discrimination bits are part
of the information that form the encrypted portion of
the transmission (Figure 4-2). After the receiver has
decrypted a transmission, the discrimination bits are
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© 2011 Microchip Technology Inc.