M16C User Manual.pdf

Timer BMitsubishi microcomputersM16C / 62 GroupSINGLE-CHIP 16-BIT CMOS MICROCOMPUTER2.3.7 Precautions for Timer B (pulse period/pulse width measurement mode)(1) The timer Bi interrupt request bit goes to “1” when an effective edge of a measurement pulseis input or timer Bi is overflowed. The factor of interrupt request can be determined by use ofthe timer Bi overflow flag within the interrupt routine.(2) If the timer overflow occurs simultaneously with the input of a measurement pulse, and if theinterrupt factor cannot be determined from the timer Bi overflow flag, connect the timers andcount 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 thetimer 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 flagonly 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 transferredto 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 Bioverflow flag may go to “1” immediately after a count is started.(7) If changing the measurement mode select bit is set after a count is started, the timer Biinterrupt request bit goes to “1”.(8) If the input signal to the TBiIN pin is affected by noise, precise measurement may not beperformed in some cases. It is recommended to see that measurements fall within a specificrange by use of software.(9) For pulse width measurement, pulse widths are successively measured. Use software tocheck whether the measurement result is an “H” level width or an “L” level width.325