Datasheet

Audio PICtail

™

Plus Daughter Board User’s Guide

The demo program consists of these basic software elements:

• ADC Driver

• Output Compare Module Driver

• Loopback Application Software

3.1.1 ADC Driver

The ADC driver reads the incoming signal on the specified 12-bit ADC channel (either

AN0 or AN3), as determined by the ADC CH SEL jumper (J9). The driver interface is

specified in the file ADCChannelDrv.h. The driver is implemented in

ADCChannelDrv.c file.

The ADC driver uses DMA Channel 0 to read data from the ADC register. The DMA

channel is configured for continuous ping-pong operation, which allows the application

to read one buffer while the DMA is populating the other buffer. Buffer memory must be

allocated by the user application.

Parameters such as instruction cycle frequency, sampling rate, buffer size and ADC

module configuration are set in the ADCChannelDrv.h header file. Refer to the driver

documentation on the CD for details.

3.1.2 Output Compare Module Driver

The Output Compare PWM (OCPWM) Driver uses the Output Compare module to

convert digital data to a PWM signal. Either Output Compare Channel 1 or Channel 2

can be used. The driver interface is specified in the file OCPWMDrv.h and the driver is

implemented in OCPWMDrv.c file.

The driver uses DMA Channel 1 to write data to the OCxRS register in the Output

Compare PWM module. This channel is configured for continuous ping-pong

operation. The buffers for the driver must be allocated by the user application.

The Timer 2 module on the dsPIC33F or PIC24H device is configured for the maximum

PWM time period. The driver maps the input sample value to a time period, which is

then loaded into the OCxRS register. The OC output stays high until the Timer 2 value

matches the OCxRS register time period and then stays low for the rest of the PWM

period. This way the duty cycle of the OC PWM signal is proportional to the input digital

sample.

Parameters such as instruction cycle frequency, sampling rate, buffer size and PWM

carrier frequency are set in the OCPWMDrv.h header file. Refer to the driver

documentation on the CD for details.