HCS473-SLROM datasheet(18/68 Pages) MICROCHIP

18 / 68 page

HCS473

DS40035C-page 16

Preliminary

 2002 Microchip Technology Inc.

FIGURE 3-6:

ENCODER OPERATION: RF ENABLE/ASK/FSK OPTIONS

3.1.4.9

SEED Button Code (SDBT)

SDBT selects which switch input(s) activate a seed

transmission. Seed transmissions are disabled by

clearing all 4 bits. If a button combination is pressed

that matches the 4-bit SDBT value, a seed code word

is transmitted as configured by the SDTM, SDLM and

SDMD options (see following sections).

The binary bit order is S3-S2-S1-S0. For example, if

you want the combination of S2 and S0 to activate a

seed transmission, use SDBT=01012.

SDBT options:

• Seed is transmitted when SDBT flags match the

button input flags

• SDBT = 00002 disables seed capability.

3.1.4.10

Time Before Seed (SDTM)

The time before seed option selects the delay from

device activation until the seed code words are trans-

mitted. If the delay is not zero, the HCS473 transmits

hopping code words until the selected time, then trans-

mits seed code words.

As code words are always completed, the seed code

word begins the first code word after the specified time.

SDTM options:

• 0s - seed code words begin immediately

•0.8s

•1.6s

•3.2s

3.1.4.11

Limited Seed (SDLM)

The limited seed option may be used to disable seed

transmission capability after a configurable number of

transmitter activations; limiting a transmitter’s ability to

be learned into a receiver. Specifically, seed transmis-

sions are disabled when the synchronization counter’s

LSB increments from 7Fh to 80h.

SDLM options:

• unlimited seed capability

• limited seed capability - counter value dependent

3.1.4.12

SEED Mode (SDMD)

The Seed mode option selects between User and Pro-

duction seed modes. Production mode functions as a

special time before seed case (SDTM).

With Production mode enabled, a seed button code

activation triggers MTX hopping code words followed

by MTX seed code words. Production mode functional-

ity is disabled when the synchronization counter’s LSB

increments from 7Fh to 80h.

SDMD options:

•User

• Production

3.1.4.13

RF Baud Rate Select (RFBSL)

The timing of code word data modulated on the DATA

pin is referred to in multiples of a basic Timing Element

RFT

E. ‘RF’ TE because the DATA pin output is typically

sent through a RF transmitter to the decoder or tran-

sponder reader.

RFT

E may be selected using the RF Baud Rate Select

(RFBSL) configuration option. RF

TE accuracy is sub-

ject to the oscillator variation over temperature and

voltage.

RFBSL options:

•100

µs RFTE

•200

µs RFTE

•400

µs RFTE

•800

µs RFTE

SWITCH

S3/RFEN

DATA

S3/RFEN

DATA

PLL

ASK:

Code Word

FSK:

Note:

Configuring S3/RFEN as RFEN (see

Section 3.1.4.8) prevents the use of S3 to

trigger a seed transmission.

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