271
10.4.6
Complementary PWM Mode
In complementary PWM mode, three pairs of complementary, non-overlapping, positive and
negative PWM waveforms can be obtained using channels 3 and 4. In complementary PWM
mode, the TIOCA3, TIOCB3, TIOCA4, TOCXA4, TIOCB4, and TOCXB4 pins become PWM
output pins and TCNT3 and TCNT4 become up-counters. Table 10.14 shows the PWM output
pins used and table 10.15 shows the settings of the registers used.
Table 10.14 Output Pins for Complementary PWM Mode
Channel
Output Pin
Description
3
TIOCA3
PWM output 1
TIOCB3
PWM output 1' (non-overlapping negative-phase waveform
of PWM output 1)
4
TIOCA4
PWM output 2
TOCXA4
PWM output 2' (non-overlapping negative-phase waveform
of PWM output 2)
TIOCB4
PWM output 3
TOCXB4
PWM output 3' (non-overlapping negative-phase waveform
of PWM output 3)
Table 10.15 Register Settings for Complementary PWM Mode
Register
Setting
TCNT3
Initial setting of non-overlap cycle (difference with TCNT4)
TCNT4
Initial setting of H'0000
GRA3
Sets upper limit of TCNT3–1
GRB3
Sets the turning point for PWM waveform output by the TIOCA3 and TIOCB3 pins
GRA4
Sets the turning point for PWM waveform output by the TIOCA4 and TOCXA4 pins
GRB4
Sets the turning point for PWM waveform output by the TIOCB4 and TOCXB4 pins
Procedure for Selecting Complementary PWM Mode (Figure 10.33):
1. Clear the STR3 and STR4 bits in TSTR to halt the timer counters. Complementary PWM
mode must be set while TCNT3 and TCNT4 are halted.
2. Set bits TPSC2–TPSC0 in TCR to select the same counter clock source for channels 3 and 4. If
an external clock source is selected, select the external clock edge with bits CKEG1 and
CKEG0 in TCR. Do not select any counter clear source with bits CCLR1 and CCLR0 in TCR.
3. Set bits CMD1 and CMD0 in TMDB to select complementary PWM mode. TIOCA3,
TIOCB3, TIOCA4, TIOCB4, TOCXA4, and TOCXB4 become PWM pins.
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