Specifications

Section 43. High-Speed PWM

High-Speed PWM

43.6.2 PWM Duty Cycle Control

The duty cycle determines the period of time that the PWM output must remain in the active state.

Each duty cycle register allows a 16-bit duty cycle value that is to be specified. The duty cycle

values can be updated any time by setting the Immediate Update Enable bit,

IUE (PWMCONx<0>). If the IUE bit (PWMCONx<0>) is ‘0’, the active Duty Cycle register (PDCx,

SDCx or MDC) updates at the start of the next PWM cycle.

The Master Duty Cycle register (MDC) enables multiple PWM generators to share a common

duty cycle register. The MDC register has an important role in Master Time Base mode.

In addition, each PWM generator has a Primary Duty Cycle register (PDCx) and a Secondary

Duty Cycle register (SDCx) that provides separate duty cycles to each PWM.

43.6.2.1 MASTER DUTY CYCLE (MDC)

The MDC register can be used to provide the same duty cycle to multiple PWM generators. The

MDC register can be used in any PWM mode, and also Master or Independent Time Base. The

Master Duty Cycle Register Select bit, MDCS (PWMCONx<8>), determines whether the duty

cycle of each of the PWMxH and PWMxL outputs are controlled by the PWM MDC register or the

PDCx and SDCx registers.

The MDC register enables sharing of the common duty cycle register among multiple PWM

generators and saves the CPU overhead required in updating multiple duty cycle registers.

43.6.2.2 PRIMARY DUTY CYCLE (PDCx)

The PDCx register can be used for generating the duty cycle for an individual PWM generator.

In the Complementary, Redundant or Push-Pull modes, the PDCx register provides the duty

cycle for both PWMxH and PWMxL outputs. In Independent Output mode, the PDCx register only

provides the duty cycle for the PWMxH output. The primary duty cycle comparison is illustrated

in Figure 43-12.

Figure 43-12: Primary Duty Cycle Comparison

43.6.2.3 SECONDARY DUTY CYCLE (SDCx)

The SDCx register is only used in Independent Output mode. It is ignored in Complementary,

Redundant and Push-Pull modes. In Independent Output mode, the SDCx register is an input

secondary duty cycle comparison is illustrated in Figure 43-13.

PDCx Register

PMTMR or PTMRx

Compare Logic

PWMxH and/or PWMxL signal

MUX

MDC Register

MDCS select

CLK

Note: In Independent Output mode, PDCx affects PWMxH only.