Software SPI Library

The mikroBasic 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.

Library configuration:

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

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 RF2_bit`
`dim SoftSpi_SDO as sbit sfr external`	Data Out line.	`dim SoftSpi_SDO as sbit at LATF3_bit`
`dim SoftSpi_CLK as sbit sfr external`	Clock line.	`dim SoftSpi_CLK as sbit at LATF6_bit`
`dim SoftSpi_SDI_Direction as sbit sfr external`	Direction of the Data In pin.	`dim SoftSpi_SDI_Direction as sbit at TRISF2_bit`
`dim SoftSpi_SDO_Direction as sbit sfr external`	Direction of the Data Out pin	`dim SoftSpi_SDO_Direction as sbit at TRISF3_bit`
`dim SoftSpi_CLK_Direction as sbit sfr external`	Direction of the Clock pin.	`dim SoftSpi_CLK_Direction as sbit at TRISF6_bit`

Soft_SPI_Init

Prototype	sub procedure 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	' DAC module connections dim SoftSpi_CLK as sbit at LATF6_bit dim SoftSpi_SDI as sbit at RF2_bit dim SoftSpi_SDO as sbit at LATF3_bit dim SoftSpi_CLK_Direction as sbit at TRISF6_bit dim SoftSpi_SDI_Direction as sbit at TRISF2_bit dim SoftSpi_SDO_Direction as sbit at TRISF3_bit ' 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.

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program Soft_SPI

' DAC module connections
dim Chip_Select as sbit at LATF0_bit
    SoftSpi_CLK as sbit at LATF6_bit
    SoftSpi_SDI as sbit at RF2_bit
    SoftSpi_SDO as sbit at LATF3_bit

dim Chip_Select_Direction as sbit at TRISF0_bit
    SoftSpi_CLK_Direction as sbit at TRISF6_bit
    SoftSpi_SDI_Direction as sbit at TRISF2_bit
    SoftSpi_SDO_Direction as sbit at TRISF3_bit
' End DAC module connections

dim value as word

sub procedure 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
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:

  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)                             ' Endless loop
    if ((RB0_bit) and (value < 4095)) then ' If RB0 button is pressed
      Inc(value)                           '   increment value
    else
      if ((RB1_bit) and (value > 0)) then  ' If RB1 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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