HCS300-SLASHP datasheet(9/28 Pages) MICROCHIP

9 / 28 page

DS21137F-page 9

HCS300

4.3

Synchronous Transmission Mode

Synchronous Transmission mode can be used to clock

the code word out using an external clock.

To enter Synchronous Transmission mode, the Pro-

gramming mode start-up sequence must be executed

as shown in Figure 4-3. If either S1 or S0 is set on the

falling edge of S2 (or S3), the device enters Synchro-

nous Transmission mode. In this mode, it functions as

a normal transmitter, with the exception that the timing

of the PWM data string is controlled externally and 16

extra bits are transmitted at the end with the code word.

The button code will be the S0, S1 value at the falling

edge of S2 or S3. The timing of the PWM data string is

controlled by supplying a clock on S2 or S3 and should

not exceed 20 kHz. The code word is the same as in

PWM mode with 16 reserved bits at the end of the

word. The reserved bits can be ignored. When in Syn-

chronous Transmission mode S2 or S3 should not be

toggled until all internal processing has been com-

pleted as shown in Figure 4-4.

FIGURE 4-3:

SYNCHRONOUS TRANSMISSION MODE

FIGURE 4-4:

CODE WORD ORGANIZATION (SYNCHRONOUS TRANSMISSION MODE)

“01,10,11”

PWM

S[1:0]

TPS TPH1 TPH2

t = 50ms

Preamble

Header

Data

Reserved

(16 bits)

Padding

(2 bits)

Button

Status

S2 S1 S0 S3

Serial Number

(28 bits)

Button

Status

S2 S1 S0 S3

DISC+ OVR

(12 bits)

Sync Counter

(16 bits)

82 Data bits

Transmitted

LSb first.

LSb

MSb

Fixed Portion

Encrypted Portion

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