Software SPI Library

The mikroC PRO for PIC32 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.

Library configuration:

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

The following variables must be defined in all projects using Software SPI Library: Description : Example :
extern sfr atomic sbit SoftSpi_SDI; Data In line. sbit SoftSpi_SDI at RF4_bit;
extern sfr atomic sbit SoftSpi_SDO; Data Out line. sbit SoftSpi_SDO at LATF3_bit;
extern sfr atomic sbit SoftSpi_CLK; Clock line. sbit SoftSpi_CLK at LATF6_bit;
extern sfr atomic sbit SoftSpi_SDI_Direction; Direction of the Data In pin. sbit SoftSpi_SDI_Direction at TRISF4_bit;
extern sfr atomic sbit SoftSpi_SDO_Direction; Direction of the Data Out pin sbit SoftSpi_SDO_Direction at TRISF3_bit;
extern sfr atomic sbit SoftSpi_CLK_Direction; Direction of the Clock pin. sbit SoftSpi_CLK_Direction at TRISF6_bit;

Library Routines

Soft_SPI_Init

Prototype

void Soft_SPI_Init();

Description

Routine initializes the software SPI module.

Parameters

None.

Returns

Nothing.

Requires

Global variables:

  • SoftSpi_SDI: Data in line
  • SoftSpi_SDO: Data out line
  • SoftSpi_CLK: Data clock line
  • SoftSpi_SDI_Direction: Direction of the Data in pin
  • SoftSpi_SDO_Direction: Direction of the Data out pin
  • SoftSpi_CLK_Direction: Direction of the Data clock pin
must be defined before using this function.
Example
// Software SPI module connections
sbit SoftSpi_SDI at RF4_bit;
sbit SoftSpi_SDO at LATF3_bit;
sbit SoftSpi_CLK at LATF6_bit;

sbit SoftSpi_SDI_Direction at TRISF4_bit;
sbit SoftSpi_SDO_Direction at TRISF3_bit;
sbit SoftSpi_CLK_Direction at TRISF6_bit;
// End Software SPI module connections
...
Soft_SPI_Init(); // Init Soft_SPI
Notes

None.

Soft_SPI_Read

Prototype

unsigned short Soft_SPI_Read(char sdata);

Description

This routine performs 3 operations simultaneously. It provides clock for the Software SPI bus, reads a byte and sends a byte.

Parameters
  • sdata: data to be sent.
Returns

Byte received via the SPI bus.

Requires

Soft SPI must be initialized before using this function. See Soft_SPI_Init routine.

Example
unsigned short data_read;
char data_send;
...
// 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);
Notes

None.

Soft_SPI_Write

Prototype

void Soft_SPI_Write(char sdata);

Description

This routine sends one byte via the Software SPI bus.

Parameters
  • sdata: data to be sent.
Returns

Nothing.

Requires

Soft SPI must be initialized before using this function. See Soft_SPI_Init.

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

None.

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.

Copy Code To ClipboardCopy Code To Clipboard
// DAC module connections
sbit Chip_Select at LATD0_bit;
sbit SoftSpi_CLK at LATD6_bit;
sbit SoftSpi_SDI at RD2_bit;
sbit SoftSpi_SDO at LATD3_bit;

sbit Chip_Select_Direction at TRISD0_bit;
sbit SoftSpi_CLK_Direction at TRISD6_bit;
sbit SoftSpi_SDI_Direction at TRISD2_bit;
sbit SoftSpi_SDO_Direction at TRISD3_bit;
// End DAC module connections

unsigned int value;

void InitMain() {
  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
}

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

  Chip_Select = 0;                       // Select DAC chip

  // Send High Byte
  temp = (valueDAC >> 8) & 0x0F;         // Store valueDAC[11..8] to temp[3..0]
  temp |= 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
}

void main() {

  CHECON = 0x32;
  AD1PCFG = 0xFFFF;                      // Configure AN pins as digital

  InitMain();                            // Perform main initialization

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

  while (1) {                            // Endless loop

    if ((RB0_bit) && (value < 4095)) {   // If RB0 button is pressed
      value++;                           //   increment value
      }
    else {
      if ((RB1_bit) && (value > 0)) {    // If RB1 button is pressed
        value--;                         //   decrement value
        }
      }

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

Copyright (c) 2002-2012 mikroElektronika. All rights reserved.
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