HCS412_11 Datasheet, PDF (7/52 Pages) Microchip Technology – KEELOQ® Code Hopping Encoder and Transponder Burglar alarm systems

TABLE 2-2: OSCILLATOR CALIBRATION
VALUE (OSCT)
OSCT3:0
Description
0111b
+
0011b
0010b
0001b
0000b
1111b
1110b
1101b
-
1000b
Slowest Oscillator Setting (long TE)
:
:
Slower (longer TE)
:
Nominal Setting
:
Faster (shorter TE)
:
:
Fastest Oscillator Setting (short TE)
FIGURE 2-7: HCS412 NORMALIZED RFTE
VERSUS TEMP
NORMALIZED
RFTE
1.10
1.08
RFTE
1.06
1.04
1.02
1.00
0.98
0.96
0.94
0.92
RFTE
0.90
-50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90
VDD LEGEND
= 2.0V
= 3.0V
= 6.0V
Temperature °C
Note: Values are for calibrated oscillator.
2.2.6 LOW VOLTAGE DETECTOR
The HCS412’s battery voltage detector detects when
the supply voltage drops below a predetermined value.
The value is selected by the Low Voltage Trip Point
Select (VLOWSEL) configuration option.
The low voltage detector result is included in encoder
transmissions (VLOW) allowing the receiver to indicate
when the transmitter battery is low (Figure 3-2).
The HCS412 indicates a low battery condition by
changing the LED operation (Figure 3-9).
© 2011 Microchip Technology Inc.
HCS412
FIGURE 2-8: TYPICAL VOLTAGE TRIP
POINTS
Volts (V)
5.0
4.8
4.6
4.4
4.2
4.0
3.8
VLOW
VLOW sel = 1
2.8
2.6
VLOW sel = 0
2.4
2.2
2.0
1.8
1.6
-40
0
50 85 ^{Temp (°C)}
Nominal VLOW trip point
TABLE 2-3: VLOWSEL OPTIONS
Nominal
VLOWSEL Trip
Point
Description
0
2.2V for 3V battery applications
1
4.4V for 6V battery applications
TABLE 2-4:
VLOW
0
1
VLOW STATUS BIT
Description
VDD is above selected trip voltage
VDD is below selected trip voltage
2.2.7 THE S2/RFEN/LC1 PIN
The S2/RFEN/LC1 pin may be used as a button input,
RF enable output or as an interface to the LF antenna.
Select between LC1 antenna interface and S2/RFEN
functionality with the button/transponder select (S2LC)
configuration option (Table 2-2).
2.2.7.1 S2 BUTTON INPUT CONSIDERATIONS
The S2/RFEN/LC1 pin defaults to LF antenna output
LC1 when the HCS412 is first connected to the supply
voltage (i.e., battery replacement).
The configuration register controlling the pin’s function
is loaded on the first device activation after battery
replacement. A desired S2 input state is therefore
enabled only after the first activation of either S0, S1 or
LC0. The transponder bias circuitry switches off and
the internal pull-down resistor is enabled when the S2/
RFEN/LC1 pin reaches button input configuration.
There will be an extra delay the first activation after
connecting to the supply voltage while the HCS412
retrieves the configuration word and configures the
pins accordingly.
DS41099D-page 7