7906 datasheet(154/531 Pages) RENESAS

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7906 Group User’s Manual Rev.2.0

8-3

TIMER B

8.2.1 Counter and Reload register (timer Bi register)

Each of timer Bi counter and reload register consists of 16 bits and has the following functions.

(1)

Functions in timer mode and event counter mode

Countdown in the counter is performed each time the count source is input. The reload register is

used to store the initial value of the counter. When a counter underflow 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 Bi register.

Table 8.2.1 lists the memory assignment of the timer Bi register.

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

reload register. The value written into the timer Bi register while counting is in progress is set only

to the reload register. In this case, the reload register’s updated contents are transferred to the

counter at the next underflow. The counter value is read out by reading out the timer Bi register.

Note: When reading from or writing to the timer Bi register, perform it in a unit of 16 bits. For more

information about the value obtained by reading the timer Bi register, refer to sections

“[Precautions for timer mode]” and “[Precautions for event counter mode].”

(2)

Functions in pulse period/pulse width measurement mode

Countup in the counter is performed each time the count source is input. The reload register is used

to retain the pulse period or pulse width measurement result. When a valid edge is input to the TBiIN

pin, the counter value is transferred to the reload register. In this mode, the value obtained by

reading the timer Bi register is the reload register’s contents, so that the measurement result is

obtained.

By using the count-type select bit (bit 4 at addresses 5B16 to 5D16), the count type can be selected

from the counter clear type and free-run type.

The operation of the counter after the counter value is transferred to the reload register is as follows;

• In the case of the counter clear type, the counter value becomes “000016”; and counting continues.

• In the case of the free-run type, the counter value does not become “000016”; and counting continues

with this counter value kept.

Note: When reading from the timer Bi register, perform it in a unit of 16 bits.

8.2 Block description

Timer Bi register

Timer B0 register

Timer B1 register

Timer B2 register

Low-order byte

Address 5016

Address 5216

Address 5416

High-order byte

Address 5116

Address 5316

Address 5516

Note: At reset, the contents of the timer Bi register

are undefined.

Table 8.2.1 Memory assignment of timer Bi registers

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