HCS300-SLASHP datasheet(11/28 Pages) MICROCHIP

11 / 28 page

DS21137F-page 11

HCS300

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)

Code Word

BACW Disabled

(All words transmitted)

BACW Enabled

(1 out of 2 transmitted)

BACW Enabled

(1 out of 4 transmitted)

Amplitude

Time

Code Word

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