HCS473_13 Datasheet, PDF (17/68 Pages) Microchip Technology – KEELOQ® 3-Axis Transcoder

3.1.4.14 Guard Time Select (GSEL)
The guard time (TG) select option determines the time
between consecutive code words when no data is
transmitted. The guard time may be selected in conjuc-
tion with the RF baud rate and preamble duty cycle to
control time-averaged power output for transmitter cer-
tification.
GSEL options:
• 3 RFTE
• 6.4 ms
• 51.2 ms
• 102.4 ms
3.1.4.15 Minimum Code Words (MTX)
The Minimum Code Words (MTX) configuration option
determines the minimum number of code words trans-
mitted when a momentary switch input is taken high for
more than TPU, or when a proximity activation occurs.
MTX options:
• 1 code word
• 2 code words
• 4 code words
• 8 code words
3.1.4.16 Timeout Select (TSEL)
The HCS473’s Timeout function prevents battery drain
should a switch input remain high (stuck button) longer
than the selectable TSEL time. After the TSEL time, the
device will return to Low-power mode.
The device will stop transmitting in Low-power mode
but there will be leakage across the stuck button input’s
internal pull-down resistor. The current draw will there-
fore be higher than if no button were stuck.
TSEL options:
• 4s
• 8s
• 16s
• 32s
3.1.4.17 Long Preamble Enable (LPRE)
Enabling the Long Preamble configuration option
extends the first code word’s preamble to a ‘long’ pre-
amble time LPRL; allowing the receiver more time to
wake and bias before the data bits arrive. The longer
preamble will be a square wave at the selected RFTE.
Subsequent code words begin with the standard pre-
amble length.
LPRE options:
• Standard 16 high pulse preamble
• Long preamble, duration defined by LPRL
HCS473
3.1.4.18 Long Preamble Length (LPRL)
The long preamble length option selects the first code
word’s preamble length when the long preamble option
(LPRE) is enabled. Only the first code word begins with
the long preamble, subsequent code words begin with
the standard 16 high pulses preamble.
LPRL options:
• 75 ms
• 100 ms
3.1.4.19 Preamble Duty Cycle (PRD)
The preamble duty cycle can be set to either 33% or
50% to limit the average power transmitted, Figure 3-7.
PRD options:
• 50% Duty Cycle
• 33% Duty Cycle
FIGURE 3-7:
PREAMBLE FORMATS
50% Duty Cycle ^{TE TE}
33% Duty Cycle ^{TE 2TE}
3.1.5 LED OPERATION
The LED pin output varies depending on whether the
device VDD is greater than VLOWSEL (a good battery) or
below VLOWSEL (a flat battery).
The LED pin will periodically be driven low as long as
the device is transmitting and the battery is good. If the
supply voltage drops below the specified VLOWSEL trip
point, the LED pin will be driven low only once for any
given device activation so long as the low battery con-
dition remains (Figure 3-8). If the battery voltage recov-
ers during the transmission, the LED will begin blinking
again.
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Preliminary
DS40035D-page 17