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UP
DOWN
UP
DOWN
2
0
3
4
1
2
3
1
2
0
3
4
1
2
0
3
1
TBCNTR
TBCNTR Direction
EPWMxA/EPWMxB
Case 2:
CMPA = 3, 25% Duty
Case 3:
CMPA = 2, 50% Duty
Case 3:
CMPA = 1, 75% Duty
Case 4:
CMPA = 0, 100% Duty
Case 1:
CMPA = 4, 0% Duty
EPWMxA/EPWMxB
EPWMxA/EPWMxB
EPWMxA/EPWMxB
EPWMxA/EPWMxB
Mode: Up-Down Count
TBPRD = 4
CAU = SET, CAD = CLEAR
0% - 100% Duty
Action-Qualifier (AQ) Submodule
When using this configuration in practice, if you load CMPA/CMPB on zero, then use CMPA/CMPB values
greater than or equal to 1. If you load CMPA/CMPB on period, then use CMPA/CMPB values less than or
equal to TBPRD-1. This means there will always be a pulse of at least one TBCLK cycle in a PWM period
which, when very short, tend to be ignored by the system.
Figure 2-20. Up-Down-Count Mode Symmetrical Waveform
The PWM waveforms in
Figure 2-21
through
Figure 2-26
show some common action-qualifier
configurations. The C-code samples in
Example 2-2
through
Example 2-7
shows how to configure an
ePWM module for each case. Some conventions used in the figures and examples are as follows:
•
TBPRD, CMPA, and CMPB refer to the value written in their respective registers. The active register,
not the shadow register, is used by the hardware.
•
CMPx, refers to either CMPA or CMPB.
•
EPWMxA and EPWMxB refer to the output signals from ePWMx
•
Up-Down means Count-up-and-down mode, Up means up-count mode and Dwn means down-count
mode
•
Sym = Symmetric, Asym = Asymmetric
42
ePWM Submodules
SPRU791D – November 2004 – Revised October 2007
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Summary of Contents for 28xxx
Page 2: ...2 SPRU791D November 2004 Revised October 2007 Submit Documentation Feedback...
Page 8: ...List of Tables 8 SPRU791D November 2004 Revised October 2007 Submit Documentation Feedback...
Page 12: ...Read This First 12 SPRU791D November 2004 Revised October 2007 Submit Documentation Feedback...
Page 68: ...ePWM Submodules 68 SPRU791D November 2004 Revised October 2007 Submit Documentation Feedback...
Page 116: ...Registers 116 SPRU791D November 2004 Revised October 2007 Submit Documentation Feedback...