HCS370_11 Datasheet, PDF (16/42 Pages) Microchip Technology – KEELOQ® Code Hopping Encoder Four selectable baud rates

HCS370
5.0 SPECIAL FEATURES
5.1 Internal RC Oscillator
The HCS370 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.
FIGURE 5-1: ASK/FSK INTERFACE
S0
SLEEP
STEP
5.2 RF Enable and PLL Interface
The RFEN pin will be driven high whenever data is
transmitted through the DATA pin.
The RFEN and DATA outputs also interface with RF
PLL’s. The PLL Interface Select (PLLSEL) configura-
tion option selects between 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 (TG). The power-up time (TPU) is the debounce
time plus the step-up regulator ramp up delay if the
Wait For Step-Up Regulator (WAIT) configuration
option is a ‘1’. The PLL step-up time (TPLL) is also used
to update the EEPROM counter.
VREG
VBAT
ASK RFEN
ASK DATA
CODE WORD
CODE WORD
FSK RFEN
FSK DATA
CODE WORD
CODE WORD
TPU
TPLL
TG
5.3 LED Output
The LED pin will be driven low while the HCS370 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
Wait 2 seconds for next
TE
button if QUEN=1
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.
DS41111E-page 16
2011 Microchip Technology Inc.