MikroElektronika books

Example 9 – Operating SPI modules

The example shows the initialization, writing, and reading data from the receive and transmit buffer register of an SPI module, respectively. The example shows the connection of the SPI2 module to the serial digital-to-analogue converter (DAC) MCP4921. The realization is carried out by using the mikroC compiler for dsPIC30F microcontrollers. Fig. 13-9 shows the electrical connection of the SPI module to the serial DAC MCP4921.

dspic-microcontrollers-programming-in-c-chapter-13-image-9

Fig. 13-9 Electrical connection of the SPI module to the serial DAC MCP4921.

const char CS_PIN = 1;
const char LD_PIN = 2;

unsigned int value;

void InitMain() {
 ADPCFG = 0xFFFF; // Set AN pins as digital

 Spi2_Init(); // Initialize SPI2 module

 TRISC.CS_PIN = 0; // Set CS pin as output
 TRISC.LD_PIN = 0; // Set LD pin as output
}//~


// DAC increments (0..4095) --> output voltage (0..Vref)
void DAC_Output(unsigned int valueDAC) {
 char temp;

 PORTC.CS_PIN = 0; // Select DAC module
 PORTC.LD_PIN = 0; // Enable data transfer

 // Send 2 bytes of valueDAC variable
 temp = (valueDAC >> 8) & 0x0F; // Prepare hi-byte for transfer
 // It's a 12-bit number, so only
 // lower nibble of high byte is used
 temp |= 0x30; // Set MCP4921 control bits
 Spi2_Write(temp); // Send data via SPI

 temp = valueDAC; // Prepare lo-byte for transfer
 Spi2_Write(temp); // Send data via SPI

 PORTC.LD_PIN = 1; // Disable data transfer
 PORTC.CS_PIN = 1; // Deselect DAC module
}//~


void main() {
 InitMain();

 value = 2047; // When program starts, DAC gives
 // the output in the mid-range

 while (1) { // Main loop
 DAC_Output(value++);
 if (value > 4095)
 value = 0;
 Delay_ms(5);
 }
}//~!