HCS410-IP Microchip Technology, HCS410-IP Datasheet - Page 12

• Manufacturer Part Number: HCS410-IP
• Description: KEELOQ CODE HOPPING ENCODER AND TRANSPONDER
• Manufacturer: Microchip Technology

HCS410
2.3.4
In order to increase the level of security in a system, it
is possible for the receiver to implement what is known
as a secure learning function. This can be done by uti-
lizing the seed value on the HCS410 which is stored in
EEPROM. Instead of the normal key generation
method being used to create the encoder key, this seed
value is used and there should not be any mathemati-
cal relationship between serial numbers and seeds for
the best security. See Section 3.7.3 for additional
details.
2.3.5
If the HCS410 is brought into a magnetic field it enters
IFF mode. In this mode it sends out ACK pulses on the
LC lines. If the HCS410 doesn't receive any response
to the first set of ack pulses within 50 ms the HCS410
will transmit a normal code hopping transmission for 2
seconds if XPRF is set in the configuration word. The
function code during this transmission is S2:S0 = 000.
2.3.6
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.
Time-out period is approximately 20 seconds.
FIGURE 2-13: QUE COUNTER TIMING DIAGRAM
DS40158C-page 12
Input
Sx
DIO
Transmission
•Patents have been applied for.
SEED TRANSMISSION
PASSIVE PROXIMITY ACTIVATION
AUTO-SHUTOFF
t = 0
1st Button Press
QUE = 00
Preliminary
2
t > 50 ms
2.3.7
The V
(Figure 2-8). V
has dropped below the low voltage trip point, approxi-
mately 2.2V or 4.4V selectable at 25 C. This V
nal is transmitted so the receiver can give an indication
to the user that the transmitter battery is low.
2.3.8
If a button is pressed, released for more than 30 ms,
and pressed again within 2 seconds of the first press,
the QUE counter is incremented (Figure 2-7). The
transmission that the HCS410 is busy with is aborted
and a new transmission is begun with the new QUE bits
set. These bits can be used by the decoder to perform
secondary functions using only a single button without
the requirement that the decoder receive more than
one completed transmission. For example if none of the
QUE bits are set the decoder only unlocks the driver’s
door, if QUE0 is set (double press on the transmitter)
the decoder unlocks all the doors.
All Buttons Released
Note 1: The QUE will not overflow.
T
LOW
LOW
2: The button must be pressed for more than
V
QUE0:QUE1: QUEUING INFORMATION
>30 ms
LOW
bit is transmitted with every transmission
50 ms.
: VOLTAGE LOW INDICATOR
LOW
is set when the operating voltage
1997 Microchip Technology Inc.
t <2
t = 0
2nd Button Press
S
QUE = 01
LOW
2
sig-