This application note describes the basic issues that
need to be addressed in order to implement digital sig-
nal processing systems using the PIC16C74 and
provides application code modules and examples for
DTMF tone generation, a 60 Hz notch filter, and a
simple PID compensator for control systems. These
routines can also be used with other PIC16C6X and
PIC16C7XXX processors with minor modifications and
the addition of external analog I/O devices.
The use of general purpose microcontrollers for
low-end digital signal processing applications has
become more commonplace these days with the avail-
ability of higher speed processors. Since most signal
processing systems consist of a host processor and
dedicated DSP chip, the use of a single microcontroller
to perform both these functions provides a simpler and
lower cost solution. In addition, the single chip design
will consume less power which is ideal for battery
powered applications. The PIC16C74 with its on-chip
A/D, PWM module, and fast CPU is an ideal candidate
for use in these low-bandwidth signal processing
applications.
A typical signal processing system includes an A/D
converter, D/A converter, and CPU that performs the
signal processing algorithm as shown in Figure 1. AN616
Digital Signal Processing with the PIC16C74
The input signal, x(t), is rst passed through an input
Author: Darius Mostow lter (commonly called the anti-aliasing lter) whose
Design Consultant function is to bandlimit the signal to below the Nyquist
rate (one half the sampling frequency) to prevent
aliasing. The signal is then digitized by the A/D
INTRODUCTION ……
