Specifications

17
• Timer Synchronisation
To allow timer channels in the ITU
to be used in synchronisation, it is
possible to set up two or more timers
so that they are simultaneously
written to via software and cleared by
compare matches or input captures.
When timer channels are put into this
mode then their input and output
events are also synchronised.
• Standard PWM Mode
Each timer channel can be
programmed to produce a single
phase PWM output. Thus the ITU
can output up to five separate
channels of PWM. In this mode
GRA controls the time when the pin
goes high,and GRB when the pin
goes low. Either GRA or GRB can
be set to clear the counter,thus
setting the frequency of the WM
output.
• AC Motor Control Outputs
To provide the PWM signals required
to drive AC machines, the ITU
provides two further PWM modes:
Complementary 6-phase PWM and
Reset Synchronised 6-phase PWM
(shown in Figure 15). The main
differences between these two modes
are the transition points for the
outputs and the provision of dead
time between the phase outputs.
• Phase Counting Mode
This mode finds use in servo control
systems,where the position and speed
feedback comes from a 2- phase
quadrature encoder. In this type of
encoder the waveforms output change
their phase relationship depending on
the direction of motion,as shown in
Figure 16
By utilising the phase counting mode
on the ITU, TCNT2 will count up
or down depending on the phase
of the incoming signals. Therefore,
the value of TCNT2 will reflect the
positional changes experienced by the
encoder.
14-bit 976.5 Hz 732.7 Hz 610 Hz 488 Hz 365 Hz
12-bit 3. 9 KHz 2.9 KHz 2. 4 KHz 2 KHz 1.5 KHz
10-bit 15.6 KHz 11.7 KHz 9. 7 KHz 7.8 KHz 5. 8 KHz
9-bit 31. 2 KHz 23.4 KHz 19.5 KHz 15.6 KHz 11.7 KHz
8-bit 62. 4 KHz 46.9 KHz 39 KHz 31. 3 KHz 23.4 KHz
7-bit 124.8 KHz 93.8 KHz 78 KHz 62.5 KHz 46. 8 KHz
PWM 16 12 10 8 6
Res. MHz MHz MHz MHz MHz
TCNT3 value
Counter cleared at compare match with GRA3
Time
GRA3
GRB3
GRA4
GRB4
H'0000
TIOCA
3
TIOCB
3
TIOCA
4
TOCXA
4
TIOCB
4
TOCXB
4
TCNT2 value
Counting up Counting down
Time
TCLKB
TCLKA
This facility removes the requirement for
extra hardware or interrupt handlers for
position monitoring. In this mode the
comparators of channel 2 can also be
used to generate interrupts, for example
when a certain position is reached.
The table below shows the PWM frequencies which can be obtained versus
device clock speed and output resolution.
Figure 15
Figure 16