HCS410 datasheet(12/36 Pages) MICROCHIP

12 / 36 page

HCS410

DS40158C-page 12

Preliminary

2.3.4

SEED TRANSMISSION

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

PASSIVE PROXIMITY ACTIVATION

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

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.

Time-out period is approximately 20 seconds.

2.3.7

VLOW: VOLTAGE LOW INDICATOR

The VLOW bit is transmitted with every transmission

(Figure 2-8). VLOW is set when the operating voltage

has dropped below the low voltage trip point, approxi-

mately 2.2V or 4.4V selectable at 25

°C. This VLOW sig-

nal is transmitted so the receiver can give an indication

to the user that the transmitter battery is low.

2.3.8

QUE0:QUE1: QUEUING INFORMATION

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.

FIGURE 2-13: QUE COUNTER TIMING DIAGRAM

Note 1: The QUE will not overﬂow.

2: The button must be pressed for more than

50 ms.

Input

DIO

Transmission

1st Button Press

All Buttons Released

2nd Button Press

TLOW>30 ms

t = 0

t > 50 ms

t <2S

t = 0

QUE = 002

QUE = 012

•Patents have been applied for.

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