HCS365 Datasheet, PDF (16/34 Pages) Microchip Technology – KEELOQ Code Hopping Encoder

HCS365
5.0 SPECIAL FEATURES
5.1 Internal RC Oscillator
The HCS365 has an onboard RC oscillator that con-
trols all the logic output timing characteristics. The
oscillator frequency varies over temperature and volt-
age variances, but stays within ±10% of the tuned
value. All the timing values specified in this document
are subject to this oscillator variation.
5.2 RF Enable and PLL Interface
The S3/SHIFT/RFEN pin of the HCS365 can be config-
ured to function as a RF enable output signal. This is
done with the RF Enable Output (RFENO) configura-
FIGURE 5-1: ASK/FSK INTERFACE
tion option. When enabled, this pin will be driven high
whenever data is transmitted through the DATA pin. If
the RFEN output is enabled it will not be possible to uti-
lize the dual encoder functionality.
In addition, the RF Enable and DATA output interfaces
with RF PLL’s. The PLL interface select (PLLSEL) con-
figuration option selects between the ASK and FSK
interfaces. Figure 5-1 shows the startup sequence for
both ASK and FSK interface options. The RFEN signal
will go low at the end of the last code word, including
the guard time.
If RFENO = 1, the RFEN pin will be driven high when-
ever data is transmitted through the DATA pin.
S0
ASK RFEN
ASK DATA
CODE WORD
CODE WORD
FSK RFEN
FSK DATA
CODE WORD
CODE WORD
TPU
TPLL
TG
TG
5.3 LED Output
The LED pin will be driven low while the HCS365 is
transmitting data. The LED On Time (TLEDON) can be
selected between 50 ms and 100 ms with the LED On
Time Select (LEDOS) configuration option. The LED
Off Time (TLEDOFF) is fixed at 500 ms. When the VDD
voltage drops below the selected VLOW trip point, the
LED will not blink unless the LED Blink (LEDBL) option
is set. If LEDBL is set and VDD is low, then the LED will
only flash once. Waveforms of the LED behavior are
shown in Figure 5-2.
For circuits with VDD greater than 3 volts, be sure to
limit the LED circuit with a series resistor. The LED out-
put can safely sink up to 25 mA but adding an external
resistor will conserve battery power. This is an open
drain output but it does have a weak pull-up capable of
driving a CMOS input.
DS41109D-page 16
Preliminary
© 2002 Microchip Technology Inc.