Texas Instruments 28xxx 사용자 설명서
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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
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.
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
through
show some common action-qualifier
configurations. The C-code samples in
through
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.
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
mode
•
Sym = Symmetric, Asym = Asymmetric
42
ePWM Submodules
SPRU791D – November 2004 – Revised October 2007