7721 datasheet(161/577 Pages) RENESAS

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TIMER A

7721 Group User’s Manual

8–42

8.6 Pulse width modulation (PWM) mode

8.6.2 Count source

In the PWM mode, the count source select bits (bits 6 and 7 at addresses 5816 to 5A16) select the count

source. Table 8.6.2 lists the count source frequency.

Table 8.6.2 Count source frequency

Count source

select bits

Count

source

f16

f64

f512

f(XIN) = 8 MHz

4 MHz

500 kHz

125 kHz

15625 Hz

Count source frequency

f(XIN) = 25 MHz

12.5 MHz

1.5625 MHz

390.625 kHz

48.8281 kHz

f(XIN) = 16 MHz

8 MHz

1 MHz

250 kHz

31250 Hz

8.6.3 Trigger

When a trigger is generated, the TAjOUT pin starts outputting PWM pulses. An internal or an external trigger

can be selected as that trigger.

An internal trigger is selected when the trigger select bits (bits 4 and 3 at addresses 5816 to 5A16) are “002”

or “012”; an external trigger is selected when the bits are “102” or “112.”

A trigger generated during outputting of PWM pulses is invalid and it does not affect the pulse output

operation.

(1)

When selecting internal trigger

A trigger is generated when “1” is written to the count start bit (address 4016).

(2)

When selecting external trigger

A trigger is generated at the falling edge of the TAjIN pin’s input signal when bit 3 at addresses 5816

to 5A16 is “0,” or at its rising edge when bit 3 is “1.” However, the trigger input is accepted only when

the count start bit is “1.”

When using an external trigger, set the port P5 direction registers’ bits which correspond to the TAjIN

pins for the input mode.

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