Chapter 15 Pulse-Width Modulation Subsystem (PWMSS).

Enhanced PWM (ePWM) Module www.ti.com
Each ePWM module can be configured to use or ignore the synchronization input. If the TBCTL[PHSEN]
bit is set, then the time-base counter (TBCNT) of the ePWM module will be automatically loaded with the
phase register (TBPHS) contents when one of the following conditions occur:
• EPWMxSYNCI: Synchronization Input Pulse: The value of the phase register is loaded into the
counter register when an input synchronization pulse is detected (TBPHS → TBCNT). This operation
occurs on the next valid time-base clock (TBCLK) edge.
• Software Forced Synchronization Pulse: Writing a 1 to the TBCTL[SWFSYNC] control bit invokes a
software forced synchronization. This pulse is ORed with the synchronization input signal, and
therefore has the same effect as a pulse on EPWMxSYNCI.
This feature enables the ePWM module to be automatically synchronized to the time base of another
ePWM module. Lead or lag phase control can be added to the waveforms generated by different ePWM
modules to synchronize them. In up-down-count mode, the TBCTL[PSHDIR] bit configures the direction of
the time-base counter immediately after a synchronization event. The new direction is independent of the
direction prior to the synchronization event. The TBPHS bit is ignored in count-up or count-down modes.
See Figure 15-13 through Figure 15-16 for examples.
Clearing the TBCTL[PHSEN] bit configures the ePWM to ignore the synchronization input pulse. The
synchronization pulse can still be allowed to flow-through to the EPWMxSYNCO and be used to
synchronize other ePWM modules. In this way, you can set up a master time-base (for example, ePWM1)
and downstream modules (ePWM2 - ePWMx) may elect to run in synchronization with the master.
15.2.2.3.4 Phase Locking the Time-Base Clocks of Multiple ePWM Modules
The TBCLKEN bit in the PWMSS_CTRL register in the Control Module can be used to globally
synchronize the time-base clocks of all enabled ePWM modules on a device. The TBCLKEN bit is part of
the chip configuration registers and is described in Chapter 9. When TBCLKEN = 0, the time-base clock of
all ePWM modules is stopped (default). When TBCLKEN = 1, all ePWM time-base clocks are started with
the rising edge of TBCLK aligned. For perfectly synchronized TBCLKs, the prescaler bits in the TBCTL
register of each ePWM module must be set identically. The proper procedure for enabling the ePWM
clocks is as follows:
1. Enable the ePWM module clocks.
2. Set TBCLKEN = 0. This will stop the time-base clock within any enabled ePWM module.
3. Configure the prescaler values and desired ePWM modes.
4. Set TBCLKEN = 1.
15.2.2.3.5 Time-Base Counter Modes and Timing Waveforms
The time-base counter operates in one of four modes:
• Up-count mode which is asymmetrical.
• Down-count mode which is asymmetrical.
• Up-down-count which is symmetrical.
• Frozen where the time-base counter is held constant at the current value.
To illustrate the operation of the first three modes, Figure 15-13 to Figure 15-16 show when events are
generated and how the time-base responds to an EPWMxSYNCI signal.
1636 Pulse-Width Modulation Subsystem (PWMSS) SPRUH73E–October 2011–Revised May 2012
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