HCS515-IP Microchip Technology, HCS515-IP Datasheet - Page 3

• Manufacturer Part Number: HCS515-IP
• Description: KEELOQ CODE HOPPING DECODER
• Manufacturer: Microchip Technology

1.3
Before a transmitter and receiver can work together,
the receiver must first ‘learn’ and store certain informa-
tion from the transmitter. This information includes a
‘check value’ of the serial number, the encoder decryp-
tion key, and current synchronization counter value.
FIGURE 1-2:
FIGURE 1-3:
1998 Microchip Technology Inc.
Encoder Decryption Key
Sync. Counter Value
EEPROM Array
Serial Number
HCS Decoder Overview
Encoder Decryption Key
Sync. Counter Value
Manufacturer Code
BASIC OPERATION OF A CODE HOPPING TRANSMITTER (ENCODER)
BASIC OPERATION OF A CODE HOPPING RECEIVER (DECODER)
EEPROM Array
Serial Number
Button Press
Information
Encryption
Algorithm
K
EE
L
Received Information
OQ
Serial Number
Check for
Match
Preliminary
Encrypted Data
32 Bits of
When a valid formatted message is detected, the
receiver first compares the serial number. If the serial
number check value is from a learned transmitter, the
message is decrypted. Next, the receiver checks the
decrypted synchronization counter value against what
is stored in memory. If the synchronization counter
value is verified, then a valid transmission message is
sent. Figure 1-3 shows the relationship between some
of the values stored by the receiver and the values
received from the transmitter.
Encrypted Data
Decryption
Algorithm
32 Bits of
K
EE
Transmitted Information
L
OQ
Serial Number
Synchronization
Decrypted
Check for
Counter
Match
Button Press
Information
HCS515
DS40183A-page 3