HCS361 datasheet(10/24 Pages) MICROCHIP

10 / 24 page

HCS361

DS40146C-page 10

Preliminary

4.0

TRANSMITTED WORD

4.1

Transmission Format (PWM)

The HCS361 transmission is made up of several parts

(Figure 4-1 and Figure 4-2). Each transmission is

begun with a preamble and a header, followed by the

encrypted and then the ﬁxed data. The actual data is

67 bits which consists of 32 bits of encrypted data and

35 bits of ﬁxed data. Each transmission is followed by

a guard period before another transmission can begin.

Refer to Table and Table for transmission timing spec-

iﬁcations. The encrypted portion provides up to four bil-

lion changing code combinations and includes the

function bits (based on which buttons were activated)

along with the synchronization counter value and dis-

crimination value. The non-encrypted portion is com-

prised of the CRC bits, VLOW bits, the function bits and

the 28/32-bit serial number. The encrypted and non-

encrypted sections combined increase the number of

combinations to 1.47 x 1020.

4.2

Code Word Organization

The HCS361 transmits a 67-bit code word when a but-

ton is pressed. The 67-bit word is constructed from a

Fixed Code portion and an Encrypted Code portion

(Figure 4-3).

The Encrypted Data is generated from 4 function bits,

2 user bits, overﬂow bit, independent mode bit, and 8

serial number bits, and the 16-bit synchronization value

(Figure 8-4).

The Non-encrypted Code Data is made up of VLOW

bit, 2 CRC bits, 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 transmit-

ted.

FIGURE 4-1:

TRANSMISSION FORMAT—VPWM = 0

TBP

LOGIC "1"

Code Word

BIT

Guard

Time

TXWAK=1

TXWAK=0

SPM=1

SPM=0

Preamble

Header

Encrypted

Data

Fixed Code

Data

BIT

LOGIC "0"

TXWAK=1

TXWAK=0

TBP

CODE WORD:

TRANSMISSION SEQUENCE:

Preamble

Sync

Encrypt

Fixed

Guard

1 CODE WORD

Preamble

Sync

Encrypt

•

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