HCS412SN datasheet(14/44 Pages) MICROCHIP

14 / 44 page

HCS412

DS41099C-page 14

Preliminary

The Code Word Blanking Enable (CWBE) option may

be used to reduce the average power of a transmission

by transmitting only every second or every fourth code

word

(Figure 3-7).

This

selectable

feature

determined in conjunction with the baud rate selection

bit RFBSL (Table 3-7).

Enabling the CWBE option may similarly allow the user

to transmit a higher amplitude transmission as the time

averaged power is reduced. CWBE effectively halves

the RF on-time for a given transmission so the RF out-

put power could theoretically be doubled while main-

taining the same time averaged output power.

FIGURE 3-7:

CODE WORD BLANKING

TABLE 3-7:

CODE WORD BLANKING ENABLE (CWBE)

3.4.4

DELAYED INCREMENT (DINC)

The HCS412’s Delayed Increment feature advances

the synchronization counter by 12 a period of TTO after

the encoder activation occurs, for additional security.

The next activation will show a synchronization counter

increase of 13, not 1.

If the active button is released before the time-out TTO

has elapsed, the device stops transmitting but remains

powered for the duration of the time-out period. The

device will then advance the stored synchronization

counter by 12 before powering down.

If the active button is released before the time-out TTO

has elapsed and another activation occurs while wait-

ing out the time-out period, the time-out counter will

RESET and the resulting transmission will contain syn-

chronization counter value +1.

3.4.5

PLL INTERFACE

If the RFEN/S2/LC1 pin is configured as an RF enable

output, the pin’s behavior is coordinated with the DATA

pin to enable a typical PLL’s ASK or FSK mode.

The PLL Interface (AFSK) configuration option controls

the output as shown in Figure 3-8.

TABLE 3-8:

PLL INTERFACE(AFSK)

3.4.6

LED OUTPUT

During normal operation (good battery), while transmit-

ting data the device’s LED pin will periodically be driven

low as indicated in Figure 3-9.

If the supply voltage drops below the trip point specified

by VLDWSEL, the LED pin will be driven low only once

for a longer period of time.

3.4.7

LONG PREAMBLE (LPRE)

Enabling the Long Preamble configuration option

extends the first code word’s 50% duty cycle preamble

to a ‘long’ preamble time TLPRE. The longer preamble

will be a square wave at the selected RFTE

(Figure 3-10).

RFBSL1:0

CWBE

PWM RFTE

Manchester RFTE

Transmit...

00b

400

µs800 µs

All code words

01b

200

µs400 µs

All code words

200

µs400 µs

Every other code word

10b

100

µs200 µs

All code words

100

µs200 µs

Every other code word

11b

100

µs200 µs

All code word

100

µs200 µs

Every fourth code word

CWBE Disabled

(All words transmitted)

CWBE Enabled

(1 out of 2 transmitted)

RF Output Amplitude = A

CWBE Enabled

(1 out of 4 transmitted)

Code

Word

Code

Word

Code

Word

Code

Word

Code

Word

Code

Word

Code

Word

Code

Word

Code

Word

Code

Word

Code

Word

Code

Word

Code

Word

Code

Word

Note: If delayed increment is enabled, the QUE

counter will not reset to 0 until timeout TTO

has elapsed.

AFSK

Description

ASK PLL Setup

FSK PLL Setup

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