Specifications

Section 43. High-Speed PWM

High-Speed PWM

43.5.7 Special Event Trigger

The High-Speed PWM module consists of a master Special Event Trigger that can be used as a

CPU interrupt source and for synchronization of analog-to-digital conversions with the PWM time

base. The analog-to-digital sampling time can be programmed to occur any time within the PWM

period. The Special Event Trigger allows the user-assigned application to minimize the delay

between the time the analog-to-digital conversion results are acquired and the time the duty cycle

value is updated. The Special Event Trigger is based on the master time base.

The master Special Event Trigger value is loaded into the PWM Special Event Compare

Postscaler Select bits (SEVTPS<3:0>) in the PWM Time Base Control register (PTCON<3:0>)

or the PWM Secondary Master Time Base Control register (STCON<3:0>), control the Special

Event Trigger operation. To generate a trigger to the ADC module, the value in the PWM Master

Time Base Counter (PMTMR/SMTMR) is compared to the value in the SEVTCMP/SSEVTCMP

ratio. The postscaler is configured by writing to the (SEVTPS<3:0>) control bits (PTCON<3:0>).

Special Event Trigger pulses are generated if the following conditions are satisfied:

• On a match condition regardless of the status of the Special Event Interrupt Enable bit,

SEIEN bit (PTCON<11>)

• If the compare value in the SEVTCMP/SSEVTCMP register is a value from zero to a

maximum value of the PTPER/STPER register

The Special Event Trigger output postscaler is cleared on these events:

• Any device Reset

• When PTEN = 0 (PTCON<15>)

The configuration of ADC special event trigger is shown in Example 43-7.

Example 43-7: ADC Special Event Trigger Configuration

In addition to generating ADC triggers, the Special Event Trigger can also be used to generate

the primary and secondary Special Event trigger interrupts, on a compare match event.

/* ADC Special Event Trigger configuration */

SEVTCMP = 1248; /* Special Event Trigger value set at ~25%

of period value (4999)*/

PTCONbits.SEVTPS = 0; /* Special Event Trigger output postscaler

set to 1:1 selection (trigger generated

every PWM cycle */

PTCONbits.SEIEN = 0; /* Special event interrupt is disabled */

while (PTCONbits.SESTAT == 0); /* Wait for special event status change */