HCS360_01 Datasheet, PDF (14/28 Pages) Microchip Technology – KEELOQ® Code Hopping Encoder

HCS360
5.5 Auto-shutoff
The Auto-shutoff function automatically stops the
device from transmitting if a button inadvertently gets
pressed for a long period of time. This will prevent the
device from draining the battery if a button gets
pressed while the transmitter is in a pocket or purse.
This function can be enabled or disabled and is
selected by setting or clearing the time-out bit
(Section 3.5.5). Setting this bit will enable the function
(turn Auto-shutoff function on) and clearing the bit will
disable the function. Time-out period is approximately
25 seconds.
5.6 VLOW: Voltage LOW Indicator
The VLOW bit is transmitted with every transmission
(Figure 4-3) and will be transmitted as a one if the
operating voltage has dropped below the low voltage
trip point, typically 3.8V at 25°C. This VLOW signal is
transmitted so the receiver can give an indication to the
user that the transmitter battery is low.
5.7 LED Output Operation
During normal transmission the LED output is LOW
while the data is being transmitted and high during the
guard time. Two voltage indications are combined into
one bit: VLOW. Table 5-1 indicates the operation value
of VLOW while data is being transmitted.
FIGURE 5-1: VLOW TRIP POINT VS.
TEMPERATURE
4.5
VLOW=0
4
Nominal Trip Point
3.8V
3.5
3.5
VLOW=1
3
2.5
2
1.5
-40
VLOW=0
Nominal Trip
Point
25
2V
85
If the supply voltage drops below the low voltage trip
point, the LED output will be toggled at approximately
1Hz during the transmission.
TABLE 5-1 VLOW AND LED VS. VDD
Approximate
Supply Voltage
Max → 3.8V
3.8V → 2.2V
2.2V → Min
Vlow Bit
0
1
0
LED Operation*
Normal
Flashing
Normal
*See also Flash operating modes.
FIGURE 5-2: BLANK ALTERNATE CODE WORD
BACW Disabled
(All words transmitted)
Amplitude
100ms
A
100ms
One Code Word
100ms
100ms
BACW Enabled
(1 out of 2 transmitted)
2A
Min Tx Length
Time
DS40152D-page 14
 2001 Microchip Technology Inc.