The mikroPascal PRO for dsPIC30/33 and PIC24 provides routines for implementing Software SPI communication. These routines are hardware independent and can be used with any MCU. The Software SPI Library provides easy communication with other devices via SPI: A/D converters, D/A converters, MAX7219, LTC1290, etc.

• SPI to Master mode
• Clock value = 20 kHz.
• Data sampled at the middle of interval.
• Clock idle state low.
• Data sampled at the middle of interval.
• Data transmitted at low to high edge.

The library configures SPI to the master mode, clock = 20kHz, data sampled at the middle of interval, clock idle state low and data transmitted at low to high edge.

  Important : The Software SPI library implements time-based activities, so interrupts need to be disabled when using it.

External dependencies of Software SPI Library

Library Routines

• Soft_SPI_Init
• Soft_SPI_Read
• Soft_SPI_Write

Soft_SPI_Init

// Software SPI module connections
var SoftSpi_SDI : sbit at RF2_bit;
var SoftSpi_SDO : sbit at LATF3_bit;
var SoftSpi_CLK : sbit at LATF6_bit;

var SoftSpi_SDI_Direction : sbit at TRISF2_bit;
var SoftSpi_SDO_Direction : sbit at TRISF3_bit;
var SoftSpi_CLK_Direction : sbit at TRISF6_bit;
// End Software SPI module connections
...
Soft_SPI_Init(); // Init Soft_SPI

Soft_SPI_Read

var data_read, data_send : byte;
...
// Read a byte and assign it to data_read variable
// (data_send byte will be sent via SPI during the Read operation)
data_read := Soft_SPI_Read(data_send);

Soft_SPI_Write

// Write a byte to the Soft SPI bus
Soft_SPI_Write(0xAA);

Library Example

This code demonstrates using library routines for Soft_SPI communication. Also, this example demonstrates working with max7219. Eight 7 segment displays are connected to MAX7219. MAX7219 is connected to SDO, SDI, SCK pins are connected accordingly.

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program Soft_SPI;

// DAC module connections
var Chip_Select : sbit at LATF0_bit;
    SoftSpi_CLK : sbit at LATF6_bit;
    SoftSpi_SDI : sbit at RF2_bit;
    SoftSpi_SDO : sbit at LATF3_bit;

var Chip_Select_Direction : sbit at TRISF0_bit;
    SoftSpi_CLK_Direction : sbit at TRISF6_bit;
    SoftSpi_SDI_Direction : sbit at TRISF2_bit;
    SoftSpi_SDO_Direction : sbit at TRISF3_bit;
// End DAC module connections

var value : word;

procedure InitMain();
  begin
    TRISB0_bit := 1;                        // Set RB0 pin as input
    TRISB1_bit := 1;                        // Set RB1 pin as input
    Chip_Select := 1;                       // Deselect DAC
    Chip_Select_Direction := 0;             // Set CS# pin as Output
    Soft_Spi_Init();                        // Initialize Soft_SPI
  end;

// DAC increments (0..4095) --> output voltage (0..Vref)
procedure DAC_Output( valueDAC : word);
var temp : byte; volatile;
  begin
    Chip_Select := 0;                        // Select DAC chip

    // Send High Byte
    temp := word(valueDAC shr 8) and 0x0F;   // Store valueDAC[11..8] to temp[3..0]
    temp := temp or 0x30;                    // Define DAC setting, see MCP4921 datasheet
    Soft_SPI_Write(temp);                    // Send high byte via Soft SPI

    // Send Low Byte
    temp := valueDAC;                        // Store valueDAC[7..0] to temp[7..0]
    Soft_SPI_Write(temp);                    // Send low byte via Soft SPI

    Chip_Select := 1;                        // Deselect DAC chip
  end;

  begin

    ADPCFG := 0xFFFF;                        // Configure AN pins as digital

    InitMain();                              // Perform main initialization

    value := 2048;                           // When program starts, DAC gives
                                             //   the output in the mid-range

    while (TRUE) do                          // Endless loop
      begin

        if ((RB0_bit) and (value < 4095)) then   // If RB0 button is pressed
          Inc(value)                             //   increment value
        else
          begin
            if ((RB1_bit) and (value > 0)) then  // If RB1 button is pressed
              Dec(value);                        //   decrement value
          end;

        DAC_Output(value);                       // Send value to DAC chip
        Delay_ms(1);                             // Slow down key repeat pace
      end;
  end.

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