Specifications

18
Modified ITU on
H8/306x, H8/3006
and H8/3007
The ITU on H8/306x,H8/3006 and
H8/3007 are modified to be more
flexible. Channels 3 and 4 can be split
into 4 timer channels (8-bit) instead of 2
timer channels (16-bit). However, this
modified ITU does not have the special
AC motor control modes
(Complementary 6-phase PWM and
Reset Synchronised 6-phase PWM). The
buffering facility has also been removed.
Timer Pulse Unit
(TPU)
The TPU is similar to the ITU, yet even
more powerful and flexible. It is found
on all H8S devices,with the H8S/224x
and the H8S/222x devices having only
half of a TPU implemented.
The TPU comprises six 16-bit timer
channels with a total of 16 Timer
General Registers (TGR),each of which
can act either as an output compare or
an input capture function. Some TGR’s
can also act as buffer registers to reduce
the interrupt load that is put onto the
CPU.
For each channel one out of eight input
clocks can be selected in software.
Possible sources are internal clocks,
external clock pins or overflow of other
timers, the latter effectively providing a
method to cascade two 16-bit timers to
form 32-bit timers.
While the ITU provides one channel for
phase counting the TPU provides four.
Also, the TPU allows to trigger an A/D
conversion and can trigger data transfers
by the Data transfer controller (DTC).
The TPU allows to generate a 15-phase
PWM signal,by using one TGR as the
cycle register and the other 15 TGR’s to
set the duty.
However,as the ITU puts more emphasis
on motor control and similar
applications,the TPU does not support
‘Reset synchronized 6-phase PWM
mode’and ‘Complementary 6-phase
PWM mode’.
16-bit Free Running
Timer (FRT)
The main timer unit of H8S/21xx is the
16-bit Free Running Timer (FRT), with
2 OC and 4 IC. The input capture
facility can also be operated in buffered
mode, with only 2 IC available in this
case.
Input clock can be selected from 3
internal clocks and an external clock,
which also allows event counting. The
FRT unit features one independent
interrupt for each IC,OC and one on
overflow.
8-bit timers
The H8S/2655-series,H8S/2355 and 53,
H8S/224x,H8S/234x and H8S/21xx all
have an additional 8-bit timer module
with two channels (TMR0 and TMR1).
Each channel has two time constant
registers (TCORA and TCORB) that
are constantly compared with the
counter value to detect compare
matches. The 8-bit timer module can
perform a variety of functions, including
pulse output with an arbitrary duty cycle
or counting events on an external pin.
The 8-bit timer module has the
following features:
• Selection of internal clock phi/8,
phi/64,phi/8192 or an external clock
input.
• Selection of counter clear sources:
compare match A or B,or external
reset
• Cascading of both channels to form a
16-bit timer
• Channel 1 can also be used to count
channel 0 compare matches
These 8-bit timers can also be used to
keep up a minimum level of timer
functionality in times of low activity of
the overall system. The result is lowest
power consumption on one hand,
because the TPU can be switched off in
that situation,but a minimum of timer
activity on the other hand. The 8-bit
timer could be used to update a software
real time clock,for example,or scan a
keyboard, so that the system can return
to full activity when a key has been
pressed.
Enhanced 8-bit
timers on H8S/21xx
H8S/21xx derivatives feature a similar 8
bit timer module as described in the
previous paragraph. However,it has a
third 8-bit timer channel TMRY, which
has similar functionality like TMR0 and
TMR1,but no output pin that is under
control of the compare match facility.
14 bit PWM timer
H8S/21xx is equipped with a two
channel PWM timer,intended for use as
a digital-to-analog converter. It is based
on a 14-bit counter,thus enabling low-
ripple, 14-bit resolution analog signals to
be generated.
Watchdog Timer
(WDT) on H8/300H
Often,a watchdog timer is a very
important feature in any embedded
application. It is used to ensure that any