HCS410_01 Datasheet, PDF (8/36 Pages) Microchip Technology – KEELOQ® Code Hopping Encoder and Transponder

HCS410
2.2.1 TRANSMISSION DATA FORMAT
The HCS410 transmission (CH Mode) is made up of
several parts (Figure 2-10 and Figure 2-11). Each
transmission is begun with a preamble and a header,
followed by the encrypted and then the fixed data. The
actual data is 69 bits which consists of 32 bits of
encrypted data and 37 bits of fixed data. Each trans-
mission is followed by a guard period before another
transmission can begin. Refer to Table 5-4
and Table 5-5 for transmission timing specifications.
The combined encrypted and nonencrypted sections
increase the number of combinations to 1.47 x 10²⁰.
The HCS410 transmits a 69-bit code word when a but-
ton is pressed. The 69-bit word is constructed from a
Fixed Code portion and Code Hopping portion
(Figure 2-8).
The Encrypted Data is generated from 4 function bits,
2 overflow bits, and 10 discrimination bits, and the 16-
bit synchronization counter value (Figure 2-8).
The Nonencrypted Code Data is made up of 2 QUE
bits, 2 CRC bits, a VLOW bit, 4 function bits, and the
28-bit serial number. If the extended serial number
(32 bits) is selected, the 4 function code bits will not be
transmitted (Figure 2-8).
FIGURE 2-8: HOP CODE WORD ORGANIZATION (RIGHT-MOST BIT IS CLOCKED OUT FIRST)
Fixed Code Data
Encrypted Code Data
QUE CRC
(Q1, Q0 _{(2 bit)}
bit)
VLOW
(1 bit)
Button
Status*
(4 bits)
S2 S1 S0 0
28-bit
Serial Number
Button Overflow (2 bits)
Status
and
(4 bits) ^{Discrimination}
S2 S1 S0 0 ^{bits (10 bits)}
16-bit
Synchronization
Counter Value
QUE ^CRC VLOW
(2 bits) (2 bits) _{(1 bit)}
+
Serial Number and
Button Status (32 bits)
MSB
LSB
69 bits
+
32 bits of Encrypted Data
of Data
Transmitted
* Optional.
FIGURE 2-9: SEED CODE WORD ORGANIZATION
Fixed Code Data
QUE0 CRC
(Q1, Q0 _{(2 bit)}
bit)
VLOW
(1 bit)
Button*
Status
(4 bits)
S2 S1 S0 0
Unencrypted
SEED
QUE ^CRC
(2 bits) (2 bits)
VLOW
(1 bit)
(B4ub+ttiotsn)
+
* Optional.
SEED
(60 bits)
69 bits
of Data
Transmitted
DS40158E-page 8
Preliminary
 2001 Microchip Technology Inc.