M16CSLASH62M datasheet(368/615 Pages) RENESAS

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Timer B

Mitsubishi microcomputers

M16C / 62A Group

SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

2-51

(1) 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.

(2) If the timer overflow occurs simultaneously with the input of a measurement pulse, and if the

interrupt factor cannot be determined from the timer Bi overflow flag, connect the timers and

count the number of overflows.

(3) When reset, the timer Bi overflow flag goes to “1”. This flag can be set to “0” by writing to the

timer Bi mode register when the count start flag is “1”.

(4) Use the timer Bi interrupt request bit to detect only overflows. Use the timer Bi overflow flag

only to determine the interrupt factor within the interrupt routine.

(5) When the first effective edge is input after a count is started, an indeterminate value is trans-

ferred to the reload register. At this time, timer Bi interrupt request is not generated.

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

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

val between a count start and an effective edge input.

(7) If changing the measurement mode select bits are set after a count is started, the timer Bi

interrupt request bit goes to “1”. Note that the timer Bi interrupt request bit does not change if

the same value as before is written to the measurement mode select bits.

(8) If the input signal to the TBiIN pin is affected by noise, precise measurement may not be

performed in some cases. It is recommended to see that measurements fall within a specific

range by use of software.

(9) For pulse width measurement, pulse widths are successively measured. Use software to

check whether the measurement result is an “H” level width or an “L” level width.

2.3.7 Precautions for Timer B (pulse period/pulse width measurement mode)

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