HCS301_11 Datasheet, PDF (12/38 Pages) Microchip Technology – Microchip Technology Inc. is a code hopping encoder designed for secure

HCS301
5.7 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.
FIGURE 5-1:
BLANK ALTERNATE CODE WORD (BACW)
Amplitude
BACW Disabled
A
(All words transmitted)
Code Word
BACW Enabled
2A
(1 out of 2 transmitted)
Code Word
Code Word
Code Word
4A
BACW Enabled
(1 out of 4 transmitted)
Time
DS21143C-page 12
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