Software SPI Library
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Software SPI Library

The mikroBasic PRO for ARM 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

Stellaris

The following variables must be defined in all projects using Software SPI Library: Description : Example :
dim SoftSpi_SDI as sbit sfr external Data In line. dim SoftSpi_SDI as sbit at GPIO_PORTJ_DATA4_bit
dim SoftSpi_SDO as sbit sfr external Data Out line. dim SoftSpi_SDO as sbit at GPIO_PORTJ_DATA5_bit
dim SoftSpi_CLK as sbit sfr external Clock line. dim SoftSpi_CLK as sbit at GPIO_PORTJ_DATA3_bit
dim SoftSpi_SDI_Direction as sbit sfr external Direction of the Data In pin. dim SoftSpi_SDI_Direction as sbit at GPIO_PORTJ_DIR4_bit
dim SoftSpi_SDO_Direction as sbit sfr external Direction of the Data Out pin dim SoftSpi_SDO_Direction as sbit at GPIO_PORTJ_DIR5_bit
dim SoftSpi_CLK_Direction as sbit sfr external Direction of the Clock pin. dim SoftSpi_CLK_Direction as sbit at GPIO_PORTJ_DIR3_bit

STM32

The following variables must be defined in all projects using Software SPI Library: Description : Example :
dim SoftSpi_SDI as sbit sfr external Data In line. dim SoftSpi_SDI as sbit at GPIOD_ODR.B4
dim SoftSpi_SDO as sbit sfr external Data Out line. dim SoftSpi_SDO as sbit at GPIOD_ODR.B5
dim SoftSpi_CLK as sbit sfr external Clock line. dim SoftSpi_CLK as sbit at GPIOD_ODR.B3

Library Routines

Soft_SPI_Init

Prototype

sub procedure Soft_SPI_Init()
Description

Routine initializes the software SPI module.
Parameters

None.
Returns

Nothing.
Requires

External dependencies of the library from the top of the page must be defined before using this function.
Example

Stellaris

'  DAC module connections
dim Chip_Select as sbit at GPIO_PORTJ_DATA1_bit
    SoftSpi_CLK as sbit at GPIO_PORTJ_DATA3_bit
    SoftSpi_SDI as sbit at GPIO_PORTJ_DATA4_bit
    SoftSpi_SDO as sbit at GPIO_PORTJ_DATA5_bit

dim Chip_Select_Direction as sbit at GPIO_PORTJ_DIR1_bit
    SoftSpi_CLK_Direction as sbit at GPIO_PORTJ_DIR3_bit
    SoftSpi_SDI_Direction as sbit at GPIO_PORTJ_DIR4_bit
    SoftSpi_SDO_Direction as sbit at GPIO_PORTJ_DIR5_bit
'  End DAC module connections
...
Soft_SPI_Init() ' Init Soft_SPI

STM32

'  DAC module connections
dim Chip_Select as sbit at GPIOD_ODR.B1
    SoftSpi_CLK as sbit at GPIOD_ODR.B3
    SoftSpi_SDI as sbit at GPIOD_ODR.B4
    SoftSpi_SDO as sbit at GPIOD_ODR.B5
'  End DAC module connections
...
Soft_SPI_Init() ' Init Soft_SPI
Notes

None.

Soft_SPI_Read

Prototype

sub function Soft_SPI_Read(dim data_ as byte) as byte
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 
dim data_read, 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)
Notes

None.

Soft_SPI_Write

Prototype

sub procedure Soft_SPI_Write(dim data_ as byte)
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($AA)
Notes

None.

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.

Stellaris

Copy Code To ClipboardCopy Code To Clipboard 
program Soft_SPI

'  DAC module connections
dim Chip_Select as sbit at GPIO_PORTJ_DATA1_bit
    SoftSpi_CLK as sbit at GPIO_PORTJ_DATA3_bit
    SoftSpi_SDI as sbit at GPIO_PORTJ_DATA4_bit
    SoftSpi_SDO as sbit at GPIO_PORTJ_DATA5_bit

dim Chip_Select_Direction as sbit at GPIO_PORTJ_DIR1_bit
    SoftSpi_CLK_Direction as sbit at GPIO_PORTJ_DIR3_bit
    SoftSpi_SDI_Direction as sbit at GPIO_PORTJ_DIR4_bit
    SoftSpi_SDO_Direction as sbit at GPIO_PORTJ_DIR5_bit
'  End DAC module connections

dim value as word

sub procedure InitMain()
  GPIO_Digital_Input(@GPIO_PORTJ_DATA_BITS, _GPIO_PINMASK_6 or _GPIO_PINMASK_7)  ' Set PJ6 and PJ7 as digital input
  GPIO_Digital_Output(@GPIO_PORTJ_DATA_BITS, _GPIO_PINMASK_1)                    ' Set PJ1 as digital output

  Chip_Select = 1                        ' Deselect DAC
  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 volatile

  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 ((GPIO_PORTJ_DATA7_bit) and (value < 4095)) then ' If PJ7 button is pressed
      Inc(value)                           '   increment value
    else
      if ((GPIO_PORTJ_DATA6_bit) and (value > 0)) then  ' If PJ6 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.

STM32

Copy Code To ClipboardCopy Code To Clipboard 
program Soft_SPI

'  DAC module connections
dim Chip_Select as sbit at GPIOD_ODR.B1
    SoftSpi_CLK as sbit at GPIOD_ODR.B3
    SoftSpi_SDI as sbit at GPIOD_ODR.B4
    SoftSpi_SDO as sbit at GPIOD_ODR.B5
'  End DAC module connections

dim value as word

sub procedure InitMain()
  GPIO_Digital_Input(@GPIOC_BASE,  _GPIO_PINMASK_6 or _GPIO_PINMASK_7) ' Set PC6 and PC7 as digital input
  GPIO_Digital_Output(@GPIOD_BASE, _GPIO_PINMASK_1)                    ' Set PD1 as digital output

  Chip_Select = 1                        ' Deselect DAC
  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 volatile

  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 ((GPIOC_IDR.B7) and (value < 4095)) then ' If PC7 button is pressed
      Inc(value)                           '   increment value
    else
      if ((GPIOC_IDR.B6) and (value > 0)) then  ' If PC6 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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