7477 datasheet(94/354 Pages) RENESAS

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1-77

7470/7471/7477/7478 GROUP USER’S MANUAL

HARDWARE

1.12 Timers

(5) PWM mode

In the PWM mode, a PWM waveform is output from the T1 pin by using Timer 3 and Timer 4.

The operations in the PWM mode are described below.

1 Start of count operation

After the count stop bit is cleared to “0,” a count operation starts. Each time a count source is

input, the contents of the timer are decremented by 1.

Note: The count stop bit is “0” immediately after reset release. Accordingly, a count operation is

automatically started immediately after reset release but no PWM waveform is output because

the PWM mode is not provided.

2 Reload operation

When the timer overflows, the value resulting from decrementing 1 from the contents of the timer

latch is transferred (reloaded) to the timer.

3 PWM output

In the PWM mode, the following operations are performed.

1 When the PWM mode is started

• The PWM waveform starts with “L.”

• Timer 3: Counts the count sources.

• Timer 4:

Stops

2When Timer 3 overflows

• The PWM waveform goes to “H.”

• Timer 3: Stops.

• Timer 4: Counts the count sources.

3 When Timer 4 overflows

• The PWM waveform goes to “L.”

• Timer 3: Counts the count sources.

• Timer 4: Stops.

The “L” width of the PWM waveform is set in Timer 3 and the “H” width is set in Timer 4.

4 Interrupt operation

2Timer interrupt

When the timer overflows, an interrupt request occurs, so that the interrupt request bit is set to

“1.” The acceptance of interrupt is controlled by the interrupt enable bit of each timer.

5 Stop of count operation

When the counter stop bit is set to “1” by software, the count operation stops. (The count operation

continues until the count stop bit is set to “1.”)

Figure 1.12.7 shows an example of the operation of the PWM output mode.

7477 Datasheet(PDF) 94 Page - Renesas Technology Corp