![Texas Instruments TMS320x2823x Скачать руководство пользователя страница 23](http://html1.mh-extra.com/html/texas-instruments/tms320x2823x/tms320x2823x_reference-manual_1095205023.webp)
PRD
4
4
4
PRD
4
1
2
3
0
1
2
3
0
1
2
3
0
Z
1
2
3
4
0
1
2
3
CTR_dir
1
2
3
4
0
1
2
3
0
Up
Down
Down
Up
T
PWM =
(TBPRD + 1) x T
TBCLK
For Up Count and Down Count
For Up and Down Count
F
PWM =
1/ (T
PWM)
T
PWM =
2 x TBPRD x T
TBCLK
F
PWM =
1 / (T
PWM)
1
2
3
4
0
1
2
3
4
0
1
2
3
0
T
PWM
Z
T
PWM
T
PWM
T
PWM
www.ti.com
ePWM Submodules
Figure 6. Time-Base Frequency and Period
2.2.3.1
Time-Base Period Shadow Register
The time-base period register (TBPRD) has a shadow register. Shadowing allows the register update to
be synchronized with the hardware. The following definitions are used to describe all shadow registers in
the ePWM module:
•
Active Register
The active register controls the hardware and is responsible for actions that the hardware causes or
invokes.
•
Shadow Register
The shadow register buffers or provides a temporary holding location for the active register. It has no
direct effect on any control hardware. At a strategic point in time the shadow register's content is
transferred to the active register. This prevents corruption or spurious operation due to the register
being asynchronously modified by software.
The memory address of the shadow period register is the same as the active register. Which register is
written to or read from is determined by the TBCTL[PRDLD] bit. This bit enables and disables the TBPRD
shadow register as follows:
•
Time-Base Period Shadow Mode:
The TBPRD shadow register is enabled when TBCTL[PRDLD] = 0. Reads from and writes to the
TBPRD memory address go to the shadow register. The shadow register contents are transferred to
the active register (TBPRD (Active)
←
TBPRD (shadow)) when the time-base counter equals zero
(TBCTR = 0x0000). By default the TBPRD shadow register is enabled.
•
Time-Base Period Immediate Load Mode:
If immediate load mode is selected (TBCTL[PRDLD] = 1), then a read from or a write to the TBPRD
23
SPRUG04A – October 2008 – Revised July 2009
TMS320x2833x, 2823x Enhanced Pulse Width Modulator (ePWM) Module
© 2008–2009, Texas Instruments Incorporated