HCS320 Datasheet, PDF(10/32 Page) Microchip Technology

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HCS320 Datasheet, PDF (10/32 Pages) Microchip Technology – KEELOQ Code Hopping Encoder

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HCS320

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, the device enters Synchronous

Transmission mode. In this mode, it functions as a nor-

mal 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. The timing of the PWM data string is con-

trolled by supplying a clock on S2 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 Synchronous

Transmission mode S2 should not be toggled until all

internal processing has been completed as shown in

Figure 4-4.

FIGURE 4-3:

SYNCHRONOUS TRANSMISSION MODE

TPS TPH1 TPH2

t = 50ms

Preamble

Header

Data

PWM

S[1:0]

â01,10,11â

FIGURE 4-4:

CODE WORD ORGANIZATION (SYNCHRONOUS TRANSMISSION MODE)

Fixed Portion

Reserved

(16 bits)

MSb

Padding

(2 bits)

Function

Code

(4-bit)

Serial Number

(28 bits)

Encrypted Portion

Function

Code

(4-bit)

DISC+ OVR Sync Counter

(12 bits)

(16 bits)

82 Data bits

LSb

Transmitted

LSb first.

DS41097C-page 10

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