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HCS410T-IST Datasheet(PDF) 11 Page - Microchip Technology |
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HCS410T-IST Datasheet(HTML) 11 Page - Microchip Technology |
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11 / 36 page  HCS410 2001 Microchip Technology Inc. Preliminary DS40158E-page 11 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 trans- mitter) 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 Sx 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 |
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