Pwm Waveform Details Of Apwm Mode Operation - Texas Instruments Concerto F28M35 Series Technical Reference Manual

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8.4.8 APWM Mode Operation

Main operating highlights of the APWM section:

The time-stamp counter bus is made available for comparison via 2 digital (32-bit) comparators.

When CAP1/2 registers are not used in capture mode, their contents can be used as Period and

Compare values in APWM mode.

Double buffering is achieved via shadow registers APRD and ACMP (CAP3/4). The shadow register

contents are transferred over to CAP1/2 registers either immediately upon a write, or on a CTR = PRD

In APWM mode, writing to CAP1/CAP2 active registers will also write the same value to the

corresponding shadow registers CAP3/CAP4. This emulates immediate mode. Writing to the shadow

registers CAP3/CAP4 will invoke the shadow mode.

During initialization, you must write to the active registers for both period and compare. This

automatically copies the initial values into the shadow values. For subsequent compare updates,

during run-time, you only need to use the shadow registers.

Figure 8-9. PWM Waveform Details Of APWM Mode Operation

The behavior of APWM active high mode (APWMPOL == 0) is as follows:

CMP = 0x00000000, output low for duration of period (0% duty)

CMP = 0x00000001, output high 1 cycle

CMP = 0x00000002, output high 2 cycles

CMP = PERIOD, output high except for 1 cycle (<100% duty)

CMP = PERIOD+1, output high for complete period (100% duty)

CMP > PERIOD+1, output high for complete period

The behavior of APWM active low mode (APWMPOL == 1) is as follows:

CMP = 0x00000000, output high for duration of period (0% duty)

CMP = 0x00000001, output low 1 cycle

CMP = 0x00000002, output low 2 cycles

CMP = PERIOD, output low except for 1 cycle (<100% duty)

CMP = PERIOD+1, output low for complete period (100% duty)

CMP > PERIOD+1, output low for complete period

SPRUH22I – April 2012 – Revised November 2019

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