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 mikroPascal compiler for dsPIC30F microcontrollers. Fig. 13-9 shows the electrical connection of the SPI module to the serial DAC MCP4921.

pic-microcontrollers-programming-dspic-in-pascal-chapter-13-image-9

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

program SPITest;
const  LOAD_PIN      = 2;  // DAC load pin
const  CS_PIN        = 1;  // DAC CS pin

var value : word;

procedure InitMain();
  begin
    TRISC.LOAD_PIN := 0;                   // LOAD pin
    TRISC.CS_PIN   := 0;                   // CS pin
    LATC.CS_PIN    := 1;                   // Set CS to inactive
    LATC.LOAD_PIN  := 0;                   // Set LOAD to inactive
    Spi2_Init_Advanced(_SPI_MASTER, _SPI_16_BIT, _SPI_PRESCALE_SEC_1, _SPI_PRESCALE_PRI_1,
                       _SPI_SS_DISABLE, _SPI_DATA_SAMPLE_MIDDLE, _SPI_CLK_IDLE_HIGH,
                       _SPI_ACTIVE_2_IDLE);        // Init SPI
  end;

// DAC increments (0..4095) --> output voltage (0..Vref)
procedure DAC_Output(valueDAC : word) ;
  begin
    while (SPI2STAT.1 = 1) do              // wait for SPI module to finish, if doing something
      nop;
    LATC.CS_PIN := 0;                      // CS enable for DAC
    SPI2BUF := 0x3000 or valueDAC;         // Write CurrentValue to DAC (0x3 is required by DAC)
    while (SPI2STAT.1 = 1) do              // Wait for SPI module to finish write
      nop;

    LATC.CS_PIN    := 1;                   // CS disable for DAC
  end;

begin
  InitMain();
  while 1 = 1 do
    begin
      value := 1;
      while value < $FFF do
       begin
         DAC_Output(value);
         Delay_ms(5);
         value := value+1;
       end;
    end;                                    //   the output in the mid-range
end.