HCS515

DS40183D-page 18

© 2002 Microchip Technology Inc.

7.0

ENCODERS

7.1

Transmission Format (PWM)

The encoder transmission is made up of several parts

(Figure 7-1).

Each

transmission

begins

with

a

preamble and a header, followed by the encrypted and

then the fixed data. The actual data is 66/69 bits, which

consist of 32 bits of encrypted data and 34/37 bits of

non-encrypted data. Each transmission is followed by

a guard period before another transmission can begin.

The code hopping portion provides up to four billion

changing code combinations and includes the button

status bits (based on which buttons were activated),

along with the synchronization counter value and some

discrimination bits. The non-code hopping portion is

comprised of the status bits, the function bits, and the

28-bit serial number. The encrypted and non-encrypted

combined sections increase the number of combina-

7.2

Code Word Organization

The HCS encoder transmits a 66/69-bit code word

when a button is pressed. The 66/69-bit word is con-

structed from a code hopping portion and a non-code

hopping portion (Figure 7-2).

The Encrypted Data is generated from four button bits,

two overflow counter bits, ten discrimination bits, and

the 16-bit synchronization counter value.

The Non-encrypted Data is made up from 2 status

bits, 4 function bits, and the 28/32-bit serial number.

FIGURE 7-1:

TRANSMISSION FORMAT (PWM)

FIGURE 7-2:

CODE WORD ORGANIZATION

LOGIC "1"

Guard

Time

50%

Encrypted

Portion

Fixed Code

Portion

LOGIC "0"

Preamble

Header

Repeat

(1-bit)

(1-bit)

Button

Status

S2 S1 S0 S3

Serial Number

(28 bits)

Button

Status

S2 S1 S0 S3

OVR

(2 bits)

DISC

(10 bits)

Sync Counter

(16 bits)

Repeat

(1-bit)

(1-bit)

Button

Status

1 1 1 1

Serial Number

(28 bits)

SEED

(32 bits)

34 bits of Fixed Portion

32 bits of Encrypted Portion

66 Data bits

Transmitted

LSb first.

LSb

MSb

MSb

LSb

SEED replaces Encrypted Portion when all button inputs are activated at the same time.