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
Figure 3-6. Time-Base Frequency and Period
3.2.2.3.1 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 memory address goes directly to the active register.
Enhanced Pulse Width Modulator (ePWM) Module
254
TMS320x2806x Microcontrollers
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
Copyright © 2022 Texas Instruments Incorporated
Содержание TMS320 2806 Series
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