M30620FCAFP datasheet(363/615 Pages) RENESAS

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Timer B

Mitsubishi microcomputers

M16C / 62A Group

SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

2-46

In pulse period/pulse width measurement mode, choose functions from those listed in Table 2.3.3. Op-

erations of the circled items are described below. Figure 2.3.8 shows the operation timing, and Figure

2.3.9 shows the set-up procedure.

2.3.4 Operation of Timer B (pulse period measurement mode)

Figure 2.3.8. Operation timing of pulse period measurement mode

Item

Set-up

Count source

Internal count source (f1 / f8 / f32 / fc32)

Pulse width measurement (interval between measurement pulse falling edge to rising edge,

and between rising edge to falling edge)

Pulse period measurement (interval between measurement pulse falling edge to falling edge)

Pulse period measurement (interval between measurement pulse rising edge to rising edge)

Measurement

mode

Table 2.3.3. Choosed functions

Operation

Note

(1) Setting the count start flag to “1” causes the counter to start counting the count source.

(2) If a measurement pulse changes from “H” to “L”, the value of the counter goes to “000016”,

and measurement is started. In this instance, an indeterminate value is transferred to the

reload register. The timer Bi interrupt request does not generate.

(3) If a measurement pulse changes from “H” to “L” again, the value of the counter is transferred

to the reload register, and the timer Bi interrupt request bit goes to “1”. Then the value of the

counter becomes “000016”, and the measurement is started again.

• The timer Bi interrupt request bit goes to “1” when an effective edge of a measurement pulse is

input or timer Bi is overflowed. The factor of interrupt request can be determined by use of the

timer Bi overflow flag within the interrupt routine.

• The value of the counter at the beginning of a count is indeterminate. Therefore, the timer Bi

overflow flag may go to “1” and timer Bi interrupt request may be generated during the interval

between a count start and an effective edge input.

• The timer Bi overflow flag is indeterminate after reset. The timer Bi overflow flag goes to “0” if

timer Bi mode register is written to when the count start flag is “1”. This flag cannot be set to “1”

by software.

Count source

Measurement pulse

Count start flag

Timer Bi interrupt

request bit

Timing at which counter

reaches “000016”

“1”

“H”

“1”

Transfer

(indeterminate value)

Reload register

← counter

transfer timing

“L”

“0”

Timer Bi overflow flag

“1”

“0”

Note 1: Counter is initialized at completion of measurement.

Note 2: Timer has overflowed.

Measurement of pulse time interval from falling edge to falling edge

Transfer

(measured value)

Cleared to “0” when interrupt request is accepted, or cleared by software

(1) Start count

(2) Start measurement

(3) Start measurement again

(Note 1)

(Note 2)

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