Datasheet

Section 12 8-Bit Timers
Rev. 4.00 Jun 06, 2006 page 305 of 1004
REJ09B0301-0400
Section 12 8-Bit Timers
12.1 Overview
The H8S/2138 Group and H8S/2134 Group 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/2138 Group also has two similar 8-bit timer channels (TMRX and 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.
TMRX has a built-in H8S/2138, but does not have a built-in H8S/2134.
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).