The mikroBasic PRO for AVR 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.

  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

' soft_spi pinout definition
dim SoftSpi_SDI as sbit at PINB6_bit            
dim SoftSpi_SDO as sbit at PORTB5_bit          
dim SoftSpi_CLK as sbit at PORTB7_bit           
dim SoftSpi_SDI_Direction as sbit at DDB6_bit  
dim SoftSpi_SDO_Direction as sbit at DDB5_bit  
dim SoftSpi_CLK_Direction as sbit at DDB7_bit
' end of soft_spi pinout definition

...
Soft_SPI_Init() ' Init Soft_SPI

Soft_SPI_Read

dim data_read as byte
    data_send as 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 Microchip's MCP4921 12-bit D/A converter.

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program Soft_SPI

' DAC module connections
dim Chip_Select as sbit at PORTB0_bit
    SoftSpi_CLK as sbit at PORTB7_bit
    SoftSpi_SDI as sbit at PINB6_bit   ' Note: Input signal
    SoftSpi_SDO as sbit at PORTB5_bit

dim Chip_Select_Direction as sbit at DDB0_bit
    SoftSpi_CLK_Direction as sbit at DDB7_bit
    SoftSpi_SDI_Direction as sbit at DDB6_bit
    SoftSpi_SDO_Direction as sbit at DDB5_bit
' End DAC module connections

dim value as word

sub procedure InitMain()
  DDA0_bit = 0                           ' Set PA0 pin as input
  DDA1_bit = 0                           ' Set PA1 pin as input
  Chip_Select = 1                        ' Deselect DAC
  Chip_Select_Direction = 1              ' Set CS# pin as Output
  Soft_Spi_Init()                        ' Initialize Soft_SPI
end sub

' DAC increments (0..4095) --> output voltage (0..Vref)
sub procedure DAC_Output(dim valueDAC as word)
dim temp as byte
  Chip_Select = 0                        ' Select DAC chip
  ' Send High Byte
  temp = word(valueDAC >> 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 sub
  
main:
  InitMain()                             ' Perform main initialization

  value = 2048                           ' When program starts, DAC gives
                                         '   the output in the mid-range
  while (TRUE)                           ' Endless loop
    if ((PINA0_bit) and (value < 4095)) then     ' If PA0 button is pressed
      Inc(value)                                 '   increment value
    else
      if ((PINA1_bit) and (value > 0)) then      ' If PA1 button is pressed
        Dec(value)                               '   decrement value
      end if
    end if

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

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