7721 datasheet(123/577 Pages) RENESAS

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TIMER A

7721 Group User’s Manual

8–4

8.2 Block description

8.2.1 Counter and reload register (timer Ai register)

Each of timer Ai counter and reload register consists of 16 bits.

Countdown in the counter is performed each time the count source is input. In the event counter mode,

it can also function as an up-counter.

The reload register is used to store the initial value of the counter. When a counter underflow or overflow

occurs, the reload register’s contents are reloaded into the counter.

A value is set to the counter and reload register by writing the value to the timer Ai register. Table 8.2.1

lists the memory assignment of the timer Ai register.

The value written into the timer Ai register while counting is not in progress is set to the counter and reload

reload time. The value obtained when reading out the timer Ai register varies according to the operating

mode. Table 8.2.2 lists reading from and writing to the timer Ai register.

Table 8.2.2 Reading from and writing to timer Ai register

Write

Written only to reload register.

Written to both of the counter

and reload register.

Operating mode

Timer mode

Event counter mode

One-shot pulse mode

Pulse width modulation (PWM) mode

Note: At reset, the contents of the timer Ai

Notes 1: Also refer to “[Precautions for timer mode]” and “[Precautions for event counter mode].”

2: When reading from and writing to the timer Ai register, perform it in a unit of 16 bits.

Read

Counter value is read out.

(Note 1)

Undefined value is read out.

Table 8.2.1 Memory assignment of timer Ai register

Timer Ai register

High-order byte

Low-order byte

Timer A0 register

Address 4716

Address 4616

Timer A1 register

Address 4916

Address 4816

Timer A2 register

Address 4B16

Address 4A16

Timer A3 register

Address 4D16

Address 4C16

Timer A4 register

Address 4F16

Address 4E16

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