HCS320 datasheet(9/38 Pages) MICROCHIP

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DS41097D-page 9

HCS320

4.0

TRANSMITTED WORD

4.1

Code Word Format

The HCS320 code word is made up of several parts

(Figure 4-1). Each code word contains a 50% duty

cycle preamble, a header, 32 bits of encrypted data and

34 bits of fixed data followed by a guard period before

another code word can begin. Refer to Table 9-3 for

code word timing.

4.2

Code Word Organization

The HCS320 transmits a 66-bit code word when a

button is pressed. The 66-bit word is constructed from

a Fixed Code portion and an Encrypted Code portion

(Figure 4-2).

The 32 bits of Encrypted Data are generated from 4

button bits, 12 discrimination bits and the 16-bit sync

value. The encrypted portion alone provides up to four

billion changing code combinations.

The 34 bits of Fixed Code Data are made up of 2 sta-

tus bits, 4 button bits and the 28-bit serial number. The

fixed and encrypted sections combined increase the

number of code combinations to 7.38 x 1019.

FIGURE 4-1:

CODE WORD FORMAT

FIGURE 4-2:

CODE WORD ORGANIZATION

LOGIC ‘0’

LOGIC ‘1’

Bit

Period

Preamble

Header

Encrypted Portion

of Transmission

Fixed Portion of

Transmission

Guard

Time

THOP

TFIX

50% Duty Cycle

Repeat

(1-bit)

VLOW

(1-bit)

Function

Code

(4-bit)

Serial Number

(28 bits)

Function

Code

(4-bit)

OVR

(2 bits)

DISC

(10 bits)

Sync Counter

(16 bits)

34 bits of Fixed Portion

32 bits of Encrypted Portion

66 Data bits

Transmitted

LSb first.

LSb

MSb

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