HCS473 Datasheet, PDF (18/68 Pages) Microchip Technology – Code Hopping Encoder and Transponder

HCS473
FIGURE 3-6:
ENCODER OPERATION: RF ENABLE/ASK/FSK OPTIONS
SWITCH
ASK: S3/RFEN
DATA
FSK: S3/RFEN
DATA
Code Word Code Word Code Word Code Word
TPU TPLL
Code Word Code Word Code Word Code Word
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=0101_2.
SDBT options:
• Seed is transmitted when SDBT flags match the
button input flags
• SDBT = 0000₂ disables seed capability.
Note:
Configuring S3/RFEN as RFEN (see
Section 3.1.4.8) prevents the use of S3 to
trigger a seed transmission.
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
RFTE. ‘RF’ TE because the DATA pin output is typically
sent through a RF transmitter to the decoder or tran-
sponder reader.
RFTE may be selected using the RF Baud Rate Select
(RFBSL) configuration option. RFTE 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
DS40035C-page 16
Preliminary
 2002 Microchip Technology Inc.