Datasheet
Section 12 8-Bit Timers
Rev. 4.00 Sep 27, 2006 page 341 of 1130
REJ09B0327-0400
Section 12 8-Bit Timers
12.1 Overview
This LSI include an 8-bit timer module with two channels (TMR0 and TMR1). Each channel has
an 8-bit counter (TCNT) and two time constant registers (TCORA and TCORB) that are
constantly compared with the TCNT value to detect compare-matches. The 8-bit timer module can
be used as a multifunction timer in a variety of applications, such as generation of a rectangular-
wave output with an arbitrary duty cycle.
The H8S/2148 Group also has two similar 8-bit timer channels (TMRX and TMRY), and the
H8S/2144 Group and H8S/2147N has one (TMRY). These channels can be used in a connected
configuration using the timer connection function. TMRX and TMRY have greater input/output
and interrupt function related restrictions than TMR0 and TMR1.
12.1.1 Features
• Selection of clock sources
TMR0, TMR1: The counter input clock can be selected from six internal clocks and an
external clock (enabling use as an external event counter).
TMRX, TMRY: The counter input clock can be selected from three internal clocks and an
external clock (enabling use as an external event counter).
• Selection of three ways to clear the counters
The counters can be cleared on compare-match A or B, or by an external reset signal.
• Timer output controlled by two compare-match signals
The timer output signal in each channel is controlled by two independent compare-match
signals, enabling the timer to be used for various applications, such as the generation of
pulse output or PWM output with an arbitrary duty cycle.
(Note: TMRY does not have a timer output pin.)
• Cascading of the two channels (TMR0, TMR1)
Operation as a 16-bit timer can be performed using channel 0 as the upper half and channel
1 as the lower half (16-bit count mode).
Channel 1 can be used to count channel 0 compare-match occurrences (compare-match
count mode).
• Multiple interrupt sources for each channel
TMR0, TMR1, TMRY: Two compare-match interrupts and one overflow interrupt can be
requested independently.
TMRX: One input capture source is available.