Information

TOF bit
CHnF bit
CNT
channel (n) output
MOD = 0x0008
CnV = 0x0005
counter
overflow
channel (n)
match
counter
overflow
...
0 1
2
3
4
5
6
7
8
0
1
2
...
previous value
Figure 35-142. EPWM signal with ELSnB:ELSnA = X:1
If (CnV = 0x0000), then the channel (n) output is a 0% duty cycle EPWM signal and
CHnF bit is not set even when there is the channel (n) match. If (CnV > MOD), then the
channel (n) output is a 100% duty cycle EPWM signal and CHnF bit is not set even when
there is the channel (n) match. Therefore, MOD must be less than 0xFFFF in order to get
a 100% duty cycle EPWM signal.
Note
The EPWM mode must be used only with CNTIN = 0x0000.
35.4.7 Center-Aligned PWM (CPWM) mode
The Center-Aligned mode is selected when:
• QUADEN = 0
• DECAPEN = 0
• COMBINE = 0, and
• CPWMS = 1
The CPWM pulse width (duty cycle) is determined by 2 × (CnV − CNTIN) and the
period is determined by 2 × (MOD − CNTIN). See the following figure. MOD must be
kept in the range of 0x0001 to 0x7FFF because values outside this range can produce
ambiguous results.
In the CPWM mode, the FTM counter counts up until it reaches MOD and then counts
down until it reaches CNTIN.
The CHnF bit is set and channel (n) interrupt is generated (if CHnIE = 1) at the channel
(n) match (FTM counter = CnV) when the FTM counting is down (at the begin of the
pulse width) and when the FTM counting is up (at the end of the pulse width).
This type of PWM signal is called center-aligned because the pulse width centers for all
channels are aligned with the value of CNTIN.
Functional description
K20 Sub-Family Reference Manual, Rev. 2, Feb 2012
754 Freescale Semiconductor, Inc.