M32C8A Datasheet, PDF (361/372 Pages) Renesas Technology Corp – RENESAS MCU M16C FAMILY / M32C/80 Series

M32C/8A Group
24. Usage Notes
24.7.3 Timer B
24.7.3.1 Timer B (Timer Mode, Event Counter Mode)
• The TBiS bit (i = 0 to 5) in the TABSR or TBSR register is set to 0 (count stops) after reset. Set the TBiS
bit to 1 (count starts) after selecting timer operating mode and setting the TBi register.
Bits TB2S to TB0S are bits 7 to 5 in the TABSR register. Bits TB5S to TB3S are bits 7 to 5 in the TBSR
register.
• The TBi register indicates a counter value while counting at any given time. However, FFFFh can be read
in the reload timing. A setting value can be read between setting the TBi register while a counter stops and
starting a counter.
24.7.3.2 Timer B (Pulse Period/Pulse Width Measurement Mode)
• To set the MR3 bit to 0 (no overflow), wait for one or more count source cycles to write to the TBiMR
register after the MR3 bit becomes 1, while the TBiS bit is set to 1.
(Technical update: TN-M16C-75-0110)
• Use the IR bit in the TBiIC register to detect overflow. The MR3 bit is used only to determine an interrupt
request source within the interrupt routine.
• When the first valid edge is input after the count starts, an undefined value is transferred to the reload
register. At this time, the timer Bi interrupt request is not generated.
• The counter value is undefined when the count starts. Therefore, the MR3 bit may become 1 (overflow) and
causes a timer Bi interrupt request to be generated before a valid edge is input.
• The IR bit may become 1 (interrupt requested) by changing bits MR1 and MR0 in the TBiMR register after
the count starts. If the same value is written to bits MR1 and MR0, the IR bit is not changed.
• Pulse width is repeatedly measured in pulse width measurement mode. Determine by program whether the
measurement result is high (“H”) or low (“L”).
• If an overflow and a valid edge input occur simultaneously in pulse period measurement mode, an interrupt
request is generated only once, which results in the valid edge not being recognized. Do not let an overflow
occur.
• In pulse width measurement mode, determine whether an interrupt source is a valid edge input or an
overflow by reading the port level in the TBi interrupt routine.
Rev.1.00 Jul 15, 2007 Page 344 of 352
REJ09B0385-0100