HCS320 Datasheet, PDF(9/32 Page) Microchip Technology

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HCS320 Datasheet, PDF (9/32 Pages) Microchip Technology – KEELOQ Code Hopping Encoder

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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 8-3 for

code word timing.

FIGURE 4-1:

CODE WORD FORMAT

TE TE TE

LOGIC â0â

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.

Bit

Period

LOGIC â1â

50% Duty Cycle

Preamble

Header

Encrypted Portion

of Transmission

THOP

Fixed Portion of

Transmission

TFIX

Guard

Time

FIGURE 4-2:

CODE WORD ORGANIZATION

34 bits of Fixed Portion

32 bits of Encrypted Portion

Repeat VLOW

(1-bit) (1-bit)

MSb

Function

Code

(4-bit)

Serial Number

(28 bits)

Function

Code

(4-bit)

OVR DISC Sync Counter

(2 bits) (10 bits) (16 bits)

LSb

66 Data bits

Transmitted

LSb first.

DS41097C-page 9

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