Page 336 - ARM Based Microcontroller Projects Using MBED

/*************************************************************************
SPI BUS SQUARE WAVE GENERATOR
=============================
This is an SPI bus project. An MCP4921 DAC is connected to SPI channel
2 of the Nucleo-F411RE development board. The program generates analog
square wave signal through the DAC with frequency of 1kHz (period=1ms)
and amplitude of 1V.
Author: Dogan Ibrahim
Date : September 2018
File : SPIDAC
**************************************************************************/
#include "mbed.h"

SPI dac( PC_3, PC_2, PC_7, PB_9); // MOSI,MISO,SCLK,SSEL
DigitalOut CS(PC_0); // CS of the DAC chip

//
// This function sends 12-bit digital data to the MCP4921 DAC. The
// HIGH byte is sent first, followed by the LOW byte
//
void DAC(unsigned int value)
{
char temp;

CS = 0; // Enable CS
//
// Send HIGH byte
//
temp = (value >> 8) & 0x0F; // Bits 8-11 in temp
temp |= 0x30; // Define DAC gain=1x
dac.write(temp); // Send HIGH byte
//
// Send LOW byte
//
temp = value;
dac.write(temp); // Send LOW byte
CS = 1; // Disable CS
}
//
// Main Program
// Generate square wave with amplitude 1V, and period 1ms
//
int main()
{
unsigned int amplitude;

amplitude = 1000 * 4095 / 3300; // 1V
CS = 1; // Disable CS

while(1)
{
DAC(amplitude); // Send 1V to DAC
wait(0.0005); // Wait 0.5ms
DAC(0); // Send 0V to DAC
wait(0.0005); // Wait 0.5ms
}
}

FIG. 12.7 Program listing.