deveopmen
Three-phase motor control timers
’
functions
Rev.B2 for proof reading
Mitsubishi Microcomputers
M32C/83 group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
162
Triangular wave modulation
To generate a PWM waveform of triangular wave modulation, set
“
0
”
in the modulation mode select bit
(bit 6 at 0308
16
). Also, set
“
1
”
in the timers A4-1, A1-1, A2-1 control bit (bit 1 at 0309
16
). In this mode,
each of timers A4, A1, and A2 has two timer registers, and alternately reloads the timer register
’
s con-
tent to the counter every time timer B2 counter
’
s content becomes 0000
16
. If
“
0
”
is set to the effective
interrupt output specification bit (bit 1 at 0308
16
), the frequency of interrupt requests that occur every
time the timer B2 counter
’
s value becomes 0000
16
can be set by use of the timer B2 counter (030D
16
)
for setting the frequency of interrupt occurrences. The frequency of occurrences is given by (setting;
setting
≠
0).
Setting
“
1
”
in the effective interrupt output specification bit (bit 1 at 0308
16
) provides the means to
choose which value of the timer A1 reload control signal to use,
“
0
”
or
“
1
”
, to cause timer B2
’
s interrupt
request to occur. To make this selection, use the effective interrupt output polarity selection bit (bit 0 at
0308
16
).
An example of U phase waveform is shown in Figure 1.16.7, and the description of waveform output
workings is given below. Set
“
1
”
in DU0 (bit 0 at 030A
16
). And set
“
0
”
in DUB0 (bit 1 at 030A
16
). In
addition, set
“
0
”
in DU1 (bit 0 at 030B
16
) and set
“
1
”
in DUB1 (bit 1 at 030B
16
). Also, set
“
0
”
in the
effective interrupt output specification bit (bit 1 at 0308
16
) to set a value in the timer B2 interrupt occur-
rence frequency set counter. By this setting, a timer B2 interrupt occurs when the timer B2 counter
’
s
content becomes 0000
16
as many as (setting) times. Furthermore, set
“
1
”
in the effective interrupt output
specification bit (bit 1 at 0308
16
), set in the effective interrupt polarity select bit (bit 0 at 0308
16
) and set
“
1
”
in the interrupt occurrence frequency set counter (030D
16
). These settings cause a timer B2 interrupt
to occur every other interval when the U phase output goes to
“
H
”
.
When the timer B2 counter
’
s content becomes 0000
16
, timer A4 starts outputting one-shot pulses. In this
instance, the content of DU1 (bit 0 at 030B
16
) and that of DU0 (bit 0 at 030A
16
) are set in the three-phase
output shift register (U phase), the content of DUB1 (bit 1 at 030B
16
) and that of DUB0 (bit 1 at 030A
16
)
are set in the three-phase shift register (U phase). After triangular wave modulation mode is selected,
however, no setting is made in the shift register even though the timer B2 counter
’
s content becomes
0000
16
.
The value of DU0 and that of DUB0 are output to the U terminal (P8
0
) and to the U terminal (P8
1
)
respectively. When the timer A4 counter counts the value written to timer A4 (034F
16
, 034E
16
) and when
timer A4 finishes outputting one-shot pulses, the three-phase shift register
’
s content is shifted one posi-
tion, and the value of DU1 and that of DUB1 are output to the U phase output signal and to U phase
output signal respectively. At this time, one-shot pulses are output from the timer for setting dead time
used for setting the time over which the
“
L
”
level of the U phase waveform doesn
’
t overlap the Low level
of the U phase waveform, which has the opposite phase of the former. The U phase waveform output
that started from the
“
H
”
level keeps its level until the timer for setting dead time finishes outputting one-
shot pulses even though the three-phase output shift register
’
s content changes from
“
1
”
to
“
0
”
by the
effect of the one-shot pulses. When the timer for setting dead time finishes outputting one-shot pulses,
“
0
”
already shifted in the three-phase shift register goes active, and the U phase waveform changes to
the Low level. When the timer B2 counter
’
s content becomes 0000
16
, the timer A4 counter starts count-
ing the value written to timer A4-1 (0307
16
, 0306
16
), and starts outputting one-shot pulses. When timer
A4 finishes outputting one-shot pulses, the three-phase shift register
’
s content is shifted one position,
but if the three-phase output shift register
’
s content changes from
“
0
”
to
“
1
”
as a result of the shift, the
output level changes from
“
L
”
to
“
H
”
without waiting for the timer for setting dead time to finish outputting
one-shot pulses. A U phase waveform is generated by these workings repeatedly. With the exception
that the three-phase output shift register on the U phase side is used, the workings in generating a U