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HCS410 Datasheet, PDF (9/36 Pages) Microchip Technology – KEELOQ CODE HOPPING ENCODER AND TRANSPONDER | |||
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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 ï¬xed data. The
actual data is 69 bits which consists of 32 bits of
encrypted data and 37 bits of ï¬xed 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 speciï¬cations.
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 overï¬ow 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 Overï¬ow (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
© 1997 Microchip Technology Inc.
Preliminary
DS40158C-page 9
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