HCS410 datasheet(8/46 Pages) MICROCHIP

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HCS410

DS40158F-page 8

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

Table 6-4

and Table 6-5 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)

FIGURE 2-9:

SEED CODE WORD ORGANIZATION

Fixed Code Data

Encrypted Code Data

69 bits

of Data

Transmitted

MSB

LSB

CRC

(2 bit)

VLOW

(1 bit)

Button

Status*

(4 bits)

28-bit

Serial Number

Overflow (2 bits)

bits (10 bits)

16-bit

Synchronization

CRC

(2 bits)

VLOW

(1 bit)

Serial Number and

Button Status (32 bits)

32 bits of Encrypted Data

QUE

(Q1, Q0

S2 S1 S0 0

Button

Status

(4 bits)

S2 S1 S0 0

(2 bits)

bit)

Counter Value

Discrimination

and

* Optional.

Fixed Code Data

69 bits

of Data

Transmitted

CRC

(2 bit)

VLOW

(1 bit)

Button*

Status

(4 bits)

CRC

(2 bits)

VLOW

(1 bit)

QUE

QUE0

(Q1, Q0

S2 S1 S0 0

(2 bits)

bit)

Unencrypted

Button

(4 bits)

SEED

(60 bits)

SEED

* Optional.

40158F.book Page 8 Wednesday, June 1, 2011 10:36 AM

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