7721 datasheet(157/577 Pages) RENESAS

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TIMER A

7721 Group User’s Manual

8–38

8.6 Pulse width modulation (PWM) mode

In this mode, the timer continuously outputs pulses which have an arbitrary width. (Refer to “Table 8.6.1.”)

Timers A2 to A4 can be used in this mode. Figure 8.6.1 shows the structures of the timer Aj mode registers

and timer Aj registers in the PWM mode.

Table 8.6.1 Specifications of PWM mode

Item

Count source

Count operation

PWM period/“H” level width

Count start condition

Count stop condition

Interrupt request occurrence timing

TAjIN pin’s function

TAjOUT pin’s function

Read from timer Aj register

Write to timer Aj register

Specifications

f2, f16, f64, or f512

q Countdown (operating as an 8-bit or 16-bit pulse width modulator)

q Reload register’s contents are reloaded at rising edge of PWM pulse,

and counting continues.

q A trigger generated during counting does not affect the counting.

<16-bit pulse width modulator>

<8-bit pulse width modulator>

q When a trigger is generated. (Note)

q Internal or external trigger can be selected by software.

When the count start bit is cleared to “0.”

At falling edge of PWM pulse

Programmable I/O port or trigger input

PWM pulse output

An undefined value is read out.

q While counting is stopped

When a value is written to the timer Aj register, it is written to both

of the reload register and counter.

q While counting is in progress

When a value is written to the timer Aj register, it is written only to

the reload register. (Transferred to the counter at the next reload

time.)

Period =

(216–1)

[s]

“H” level width =

[s]

Period =

(m + 1)(28–1)

“H” level width =

[s]

n(m + 1)

n : Timer Aj register’s set value

[s]

m : Timer Aj register low-order 8 bits’

set value

n : Timer Aj register high-order 8

bits’ set value

Note: The trigger is generated with the count start bit = “1.”

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