Conversion Triggers

Click Play ► to listen to the commentary.

In Analog-to-Digital Converter (ADC) operation, conversion triggers determine when a sampled analog signal is digitized.

Each data channel provides flexible conversion trigger options, depending on the conversion mode and setting of the TRG1SRC[5:0] and TRG2SRC[5:0] bits in the ADnCHxCON1 register.

In this section, we will provide an overview of several primary conversion types and features:

• Triggers Overview
• Software Trigger
  • This trigger initiates conversions directly from the application code, allowing precise synchronization with software events.
• Back-to-Back Trigger
  • This trigger automatically starts each new conversion as soon as the previous one finishes, making it ideal for rapid, continuous sampling.
• ADC Repeat Timer Trigger
  • This trigger generates periodic conversion triggers based on a programmable timer, which is well-suited for regular, time-based sampling requirements.
• Peripheral and Pin Trigger
  • This trigger uses signals from external pins or on-chip peripherals (such as PWM, timers, or logic cells) to synchronize conversions with hardware events.
• Trigger Conversion Priority

Triggers Overview

Click Play ► to listen to the commentary.

Two key points are essential to understanding conversion triggers:

• Trigger Source 1 (TRG1SRC[5:0]) initiates the start of the conversion process and is always required.
• Trigger Source 2 (TRG2SRC[5:0] initiates each subsequent conversion in multi-sample modes.

Triggers are always properly synchronized with the core’s free-running, asynchronous conversion clock to ensure accurate data collection.

The following graphic summarizes when/where each trigger source selection field is used:

Back to Top

Software Trigger

Click Play ► to listen to the commentary.

• Benefits
  • The software trigger allows the user application code to directly initiate ADC conversions, making it easy to synchronize sampling with code execution.

• How to generate a trigger
  • To enable software triggering, set Trigger 1 (TRG1SRC[5:0]) to ‘000001’.

• How it works
  • The software trigger is generated when the corresponding bit in the ADnSWTRG register is asserted.
    • Example code to trigger a conversion on ADC1 and Data Channel 1: AD1SWTRGbits.CH1TRG = 1;
  • Software trigger can be used to:
    • Start a single sample conversion,
    • Begin a multi-sample conversion sequence, and
    • Trigger subsequent conversions in multi-sample modes.
  • Software triggers can also be used to initiate conversions within a window, but cannot define the window itself in Window mode.
  • Trigger timing occurs in the processor clock domain and requires synchronization to the ADC timing domain.

• Configuration example
  • ADnCHxCON1bits.TRG1SRC = 1;   // Software trigger for initial conversion

Back to Top

Back-to-Back Trigger

Click Play ► to listen to the commentary.

• Benefits
  • The back-to-back trigger enables the accumulation of multiple samples for detailed analysis.
  • Conversions continue automatically until the specified sample count is reached.

• How to generate a trigger
  • Set Trigger 1 (TRG1SRC[5:0]) to the initial trigger source.
  • Set Trigger 2 (TRG2SRC[5:0]) to ‘000010’ to enable back-to-back operation.

• How it works
  • Each new conversion starts immediately after the previous one completes, ensuring seamless back-to-back sampling.
  • This trigger produces a continuous stream of conversion signals for uninterrupted multi-sample data collection.
  • Trigger timing is managed in the ADC clock domain for precise control.

• Configuration example
  • ADnCHxCON1bits.TRG1SRC = 1;   // Software trigger for initial conversion
  • ADnCHxCON1bits.TRG2SRC = 2;   // Immediate re-trigger for subsequent conversions

Back to Top

ADC Repeat Timer Trigger

Click Play ► to listen to the commentary.

• Benefits
  • The ADC Repeat Timer trigger enables automatic, repeated conversions until the desired count is reached.
  • Flexible trigger periods let you customize the conversion rates for your application.

• How to generate a trigger
  • Set Trigger 1 (TRG1SRC[5:0]) to the initial trigger source.
  • Set Trigger 2 (TRG2SRC[5:0]) to ‘000011’ to enable ADC Repeat Timer operation.

• How it works
  • When the internal counter matches the value in RPTCNT[5:0], a trigger event is generated.
  • The repeat timer delivers periodic, customizable triggers (adjustable TAD cycles between triggers), ideal for multi-sample operations
  • This method ensures fair allocation of ADC bandwidth across all channels. (In between triggers, other channels can be serviced)
  • Triggers are generated in the ADC clock domain, minimizing synchronization delays.

• Configuration example
  • ADnCHxCON1bits.TRG1SRC = 1;  // Software trigger (or other available choices for Trigger 1)
  • ADnCHxCON1bits.TRG2SRC = 3;   // Conversion Repeat Timer trigger

Back to Top

Peripheral and Pin Trigger

Click Play ► to listen to the commentary.

• Benefits
  • Peripheral and pin triggers allow Data Channel conversions to be initiated directly by hardware events.
  • This trigger type ensures conversions are precisely synchronized with the active state of the peripheral.

• How to generate a trigger
  • Set Trigger 1 (TRG1SRC[5:0]) to any value from ‘000001’ to ‘100111’, and/or Trigger 2 (TRG2SRC[5:0]) to any value from ‘000100’ to ‘100111’ to enable peripherals and pin trigger operation.

• How it works
  • Conversions can be triggered by peripherals such as Pulse Width Modulation (PWM), MCCP/SCCP (OCMP/ICAP), Peripheral Trigger Generator (PTG), Integrated Touch Controller (ITC), or Configurable Logic Cell outputs.
  • An external pin can also be used as a trigger source.
  • This trigger method enables precise synchronization of data conversions for applications such as motor control and digital power applications.
• The peripheral and pin trigger mechanism fully supports touch sensors and other advanced applications.
  • Trigger timing occurs in the processor clock domain and requires synchronization to the ADC timing domain.

• Configuration example
  • ADnCHxCON1bits.TRG1SRC = 4;  // PWM 1 ADC trigger 1
  • ADnCHxCON1bits.TRG2SRC = 4;  // PWM 1 ADC trigger 2

Back to Top

Trigger Conversion Priority

Click Play ► to listen to the commentary.

Channel priorities influence when each data channel is converted. Recall that the lowest data channel number has the highest priority. For oversampling conversion, it can be made non-interruptible by enabling the Oversampling Burst mode bit (ACCBRST = 1).