Section 9 Timers
Rev. 7.00 Mar 10, 2005 page 246 of 652
REJ09B0042-0700
Name Functions Internal Clock
Event
Input Pin
Waveform
Output Pin Remarks
Asynchro-
nous event
counter
• 16-bit counter
• Also usable as two
independent 8-bit
counters
• Counts events
asynchronous to φ and φw
• Can count asynchronous
events (rising/falling/both
edges) independ-ently of
the MCU's internal clock
φ/2 to φ/8
(3 choices)
AEVL
AEVH
IRQAEC
—
Note: * The watchdog timer functions differently on the H8/38024, H8/38024S, H8/38024R Group
and H8/38124 Group. See section 9.6, Watchdog Timer, for details.
9.2 Timer A
9.2.1 Overview
Timer A is an 8-bit timer with interval timing and real-time clock time-base functions. The clock
time-base function is available when a 32.768 kHz crystal resonator is connected as the subclock.
Features
Features of timer A are given below.
• Choice of eight internal clock sources (φ/8192, φ/4096, φ/2048, φ/512, φ/256, φ/128, φ/32,
φ/8).
• Choice of four overflow periods (1 s, 0.5 s, 0.25 s, 31.25 ms) when timer A is used as a clock
time base (using a 32.768 kHz crystal resonator is connected as the subclock).
• An interrupt is requested when the counter overflows.
• Use of module standby mode enables this module to be placed in standby mode independently
when not used.
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