Ibrahim Dogan - Advanced PIC Microcontroller Projects in C

Usart_Init(9600); // Set baud rate

for (;;) // Endless loop

{

while(!User_Data_Ready()); // Wait for data byte

Temp = Usart_Read(); // Read data byte

Temp++; // Increment data byte

Usart_Write(Temp); // Send the byte byte

}

}

Figure 4.26: Program listing of Example 4.14

In PIC microcontrollers that have more than one USART, the second USART is accessed by appending a “2” to the end of the function (e.g., Usart_Write2 , Usart_Read2 , etc.).

Functions in the sound library make it possible to generate sounds in our applications. A speaker (e.g., a piezo speaker) should be connected to the required microcontroller port. The following functions are offered by the sound library:

• Sound_Init

• Sound_Play

The Sound_Init function initializes the sound library and requires two parameters: the name and the bit number of the port where the speaker is connected. The address of the port name should be passed to the function. For example, if the speaker is connected to bit 3 of PORTB, then the function should be called as:

Sount_Init(&PORTB, 3);

The Sound_Play function plays a sound at a specified port pin. The function receives two arguments: the period divided by 10 (TDIV) and the number of periods (N). The first parameter is the period in microcontroller cycles divided by 10. The second parameter specifies the duration (number of clock periods) of the sound.

The following formula calculates the value used as the first parameter:

where

TDIV is the number to be used as the first parameter

F is the required sound frequency (Hz)

f is the microcontroller clock frequency (Hz)

Write a program to play a sound at 1KHz, assuming the clock frequency is 4MHz. The required duration of the sound is 250 periods.

The first parameter is calculated as follows:

Since the required duration is 250 periods, the function is called with the parameters:

Sound_Play(100, 250);

The ANSI C library consists of the following libraries (further details on these libraries are available in the mikroC user manual):

• Ctype library

• Math library

• Stdlib library

• String library

The functions in the Ctype library are mainly used for testing or data conversion. Table 4.6 lists the commonly used functions in this library.

Table 4.6: Commonly used Ctype library functions

The functions in the Math library are used for floating point mathematical operations. Table 4.7 lists the commonly used functions in this library.

Table 4.7: Commonly used Math library functions

The Stdlib library contains standard library functions. Table 4.8 lists the commonly used functions in this library.

Table 4.8: Commonly used Stdlib library functions

Write a program to calculate the trigonometric sine of the angles from 0° to 90° in steps of 1° and store the result in an array called Trig_Sine .

The required program listing is shown in Figure 4.27 (program SINE.C). A loop is created using a for statement, and inside this loop the sine of the angles are calculated and stored in array Trig_Sine. Note that the angles must be converted into radians before they are used in function sin .

/******************************************************************

TRIGONOMETRIC SINE OF ANGLES 0 to 90 DEGREES

==========================================

This program calculates the trigonometric sine of angles from 0 degrees to

90 degrees in steps of 1 degree. The results are stored in an array called

Trig_Sine.

Programmer: Dogan Ibrahim

File: SINE.C

Date: May, 2007