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HCS200 Datasheet(PDF) 9 Page - Microchip Technology |
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HCS200 Datasheet(HTML) 9 Page - Microchip Technology |
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9 / 34 page  © 2011 Microchip Technology Inc. DS40138D-page 9 HCS200 5.0 SPECIAL FEATURES 5.1 Code Word Completion The code word completion feature ensures that entire code words are transmitted, even if the button is released before the code word is complete. If the but- ton is held down beyond the time for one code word, multiple code words will result. If another button is acti- vated during a transmission, the active transmission will be aborted and a new transmission will begin using the new button information. 5.2 Blank Alternate Code Word Federal Communications Commission (FCC) part 15 rules specify the limits on worst case average funda- mental power and harmonics that can be transmitted in a 100 ms window. For FCC approval purposes, it may therefore be advantageous to minimize the transmis- sion duty cycle. This can be achieved by minimizing the duty cycle of the individual bits as well as by blanking out consecutive code words. Blank Alternate Code Word (BACW) may be used to reduce the average power of a transmission by transmitting only every sec- ond code word (Figure 5-1). This is a selectable feature that is determined in conjunction with the baud rate selection bit BSL0. Enabling the BACW option may likewise allow the user to transmit a higher amplitude transmission as the time averaged power is reduced. BACW effectively halves the RF on time for a given transmission so the RF out- put power could theoretically be doubled while main- taining the same time averaged output power. 5.3 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 learn function. This can be done by utilizing the seed value stored in EEPROM, transmitted only when all three button inputs are pressed at the same time (Table 5-1). Instead of the normal key generation inputs being used to create the crypt key, this seed value is used. 5.4 VLOW: Voltage LOW Indicator The VLOW signal is transmitted so the receiver can give an indication to the user that the transmitter battery is low. The VLOW bit is included in every transmission (Figure 4-2 and Figure 9-5) and will be transmitted as a zero if the operating voltage is above the low voltage trip point. Refer to Figure 4-2. The trip point is select- able based on the battery voltage being used. See Sec- tion 3.6.3 for a description of how the low voltage trip point is configured. FIGURE 5-1: BLANK ALTERNATE CODE WORD (BACW) TABLE 5-1: PIN ACTIVATION TABLE External Internal S2 S1 S0 S3 S2 S1 S0 Standby 0 0 000 00 Hopping Code Transmission 0 0 100 01 0 1 000 10 0 1 100 11 1 0 011 00 1 0 111 10 1 1 011 10 Seed Transmission 1 1 111 11 BACW Disabled (All words transmitted) BACW Enabled (1 out of 2 transmitted) A 2A Transmission Amplitude = A Code Word Code Word Code Word Code Word Code Word Code Word Code Word Code Word |
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Similar Description - HCS200_11 |
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