7545 datasheet(29/62 Pages) RENESAS

29 / 62 page

Rev.1.06

Mar 07, 2008

Page 29 of 59

REJ03B0140-0106

7545 Group

4. Carrier wave generating circuit

The carrier wave generating circuit is used to generate the control

wave of the remote control by using timer 2 and timer 3 (Figure

26).

In order to use the carrier wave generating function by timer 2,

set “1” to the carrier wave output valid bit (bit 1 of the carrier

wave control register (address 2716)).

Carrier wave “H” duration is set to the timer 2 primary, and

carrier wave “L” duration is set to the timer 2 secondary. Timer 2

counts a primary latch and a secondary latch alternately, and

controls carrier wave “H” duration and the “L” duration (Figure

27).

The “H” duration of the carrier waveform can be expanded for a

half clock of timer 2 count source by setting “1” to the carrier

wave “H” duration bit (bit 0) (Figure 28).

Therefore, the frequency of the carrier wave can be set by the

resolution of 1/2 of the timer 2 count source.

For example, the carrier wave of the resolution of 125 ns (max.)

can be generated at f(XIN) = 4 MHz when f(XIN)/1 is selected for

the timer 2 count source.

In order to initialize the carrier waveform, write in the timer 2

primary after stopping the count of timer 2, and then, start the

count of timer 2 . The output of the carrier waveform is started

from a primary period.

Output/stop of the carrier waveform can be controlled by

software or timer 3 (Figure 31 and Figure 32). The output of the

carrier wave is started from the P42/CARR pin when “1” is set to

the software carrier wave output bit (bit 2), and the output of the

carrier wave is stopped when “0” is written.

The auto-output of the carrier wave using timer 3 can be

performed by setting “1” to the carrier wave auto-output control

bit (bit 3) (Figure 29). Each time timer 3 underflow occurs, the

trigger signal which is used to turn the output of the carrier wave

on/off is generated.

The trigger from timer 3 becomes valid by setting “1” to the

carrier wave output trigger bit (bit 4), and the output/stop of the

carrier wave from the P42/CARR pin is repeated each time timer

3 underflows. Timer 3 count continues without stopping though

the output/stop state of the carrier wave at that time is maintained

when “0” is written to the carrier wave auto-output control bit

(bit 3) while the output of the carrier wave by timer 3 is

controlled.

In order to initialize output/stop control of the carrier waveform,

write in the timer 3 after stopping the count of timer 3, and then,

start the count of timer 3. The output of the carrier waveform is

started from “waveform output valid period”.

5. 455 kHz carrier wave generating mode

The 455 kHz carrier wave generating mode is used to generate

artificially the 455 kHz carrier wave by auto-control of the

setting value of the timer, or the waveform expansion mode.

If “1” (valid) is set to the 455 kHz carrier wave generating mode

bit (bit 5), the values of the timer latch and the carrier wave “H”

duration expansion bit (bit 0) are automatically set.

Then, the nine waveforms of 2.250

µs wavelength and the seven

waveforms of 2.125

µs wavelength are generated periodically as

shown in Figure 30.

The carrier wave of 455.516 kHz can be pseudo generated since

the average wavelength for one period becomes 2.195

µs.

In order to use 455 kHz carrier wave generating mode, use the 4

MHz oscillator and select f(XIN)/1 for the timer 2 count source.

Fig. 25 Carrier wave control register

Carrier wave control register

(CARCNT : address 002716, initial value: 0016)

Carrier wave “H” duration expansion bit

0: “H” duration expansion function invalid

1: “H” duration expansion function valid

Disable (return “0” when read)

Carrier wave output valid bit

0: Carrier wave generating function invalid

1: Carrier wave generating function valid

Software carrier wave output bit

0: Output invalid

1: Output valid

Carrier wave auto-output control bit

0: Auto-control by timer 3 invalid

1: Auto-control by timer 3 valid

Carrier wave output trigger bit

0: Carrier wave output trigger invalid

1: Carrier wave output trigger valid

455 kHz carrier wave generating mode bit

0: 455 kHz carrier wave generating mode

invalid

1: 455 kHz carrier wave generating mode

valid

Carrier wave output level bit

0: Positive waveform

1: Inverted waveform

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