dac.pbas

dac example with microcontroller implementation in c++

'*******************************************************************************
' microcontroller: P16F877A
'
'  Project name: DAC
'
' This project is designed to work with PIC 16F877A; with minor adjustments,
' it should work with any other PIC MCU that has the SPI interface.
'
' This is a sample program which demonstrates the use of the Microchip's MCP4921
' 12-bit D/A converter with PIC mcu's. This device accepts digital input (number
' from 0..4095) and transforms it to the output voltage, ranging from 0..Vref.
' In this example the D/A is connected to PORTC and communicates with PIC through
' the SPI. The reference voltage on the mikroElektronika's DAC module is 5 V.
' NOTE: in this example, the entire DAC's resolution range (12bit -> 4096
'   increments) is covered, meaning you'll need to hold a button for about
'   7 minutes to get from mid-range to the end-of-range.
'
' Tested on P16F877A.
'*******************************************************************************
program dac

const CHIP_SELECT  = 0
dim value as word

sub procedure Init
  SetBit(TRISB,0)
  SetBit(TRISB,1)
  SPI_init
  ClearBit(TRISC,CHIP_SELECT)
end sub

' DAC increments (0..4095) --> output voltage (0..Vref)
sub procedure DAC_Output(dim Value as word)
dim temp as byte
  ClearBit(PORTC,CHIP_SELECT)        ' Prepare for data transfer
  temp = hi(Value) and $0F           ' Prepare hi-byte for transfer
  temp = temp or $30                 ' It's a 12-bit number, so only
  SPI_Write(temp)                    '   lower nibble of high byte is used
  temp = lo(Value)                   ' Prepare lo-byte for transfer
  SPI_Write(temp)
  SetBit(PORTC,CHIP_SELECT)
end sub

'main procedure
main:
  Init
  DAC_Output(2048)                         ' When program starts, DAC gives
  value = 2048                             '   the output in the mid-range

  while true                               ' Main loop
    if (Button(portb,0,1,1)=true)
     and (value < 4095) then               ' Test button on B0 (increment)
      Inc(value)
    else
      if (Button(portb,1,1,1)=true)        ' If RB0 is not active then test
       and (value > 0) then                '   RB1 (decrement)
         Dec(value)
      end if
    end if
    DAC_Output(value)                      ' Perform output
    Delay_ms(200)                          ' Slow down key repeat pace
  wend

end.