DDS Sinewave Generator
using the
5-bit DAC Peripheral

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' Let's find out together what makes a PIC Tick!
'
' DDS algorithm for generating a sinewave from the 5-bit DAC on a PIC16F1823 device.
' Written for the Positron8 compiler by Les Johnson.
'
' A simple low pass filter circuit, as shown below, can be used to get a sine waveform out.
' The filter's components will need to be changed for different frequency sine waves.
'
' | 1K
' PORTA.0 |----/\/\/\-----o-----> Output
' | |
' | __|__
' PORTA.1 |--- +5V _____ 10nF
' | |
' | |
' | -----
' --- Gnd
'
Device = 16F1823 ' Tell the compiler what device it will compile for
Declare Xtal = 16 ' Tell the compiler what frequency the device will be operating at

'-----------------------------------------------------------------------------------------
' The main program starts here
'
Main:
Setup() ' Setup the program
DDS_SineWave(1000, 10000) ' Output a 1 KHz sinewave for approx 10 seconds

'-----------------------------------------------------------------------------------------
' Generate a sinewave signal from the 5-bit DAC pin
' Input : pFreq holds the DDS value for the frequency to generate
' : pDuration holds the approximate time (in ms) for the waveform to be outputted
' Output : None
' Notes : None
'
Proc DDS_SineWave(pFreq As Dword, pDuration As Dword)
Dim lAccum As Long ' Accumulator for the DDS
Symbol cDivisor = (((_xtal / 4) * 1000000) / 2240.5) ' Create a divisor for the device's frequency and the loop speed
Symbol cMult = (65536.0 / cDivisor) ' Create a floating point multiplier constant
'
' Sine wave data for the 5-bit DAC
'
Dim SineTable As Flash8 = {16, 17, 19, 20, 21, 23, 24, 25,
26, 27, 28, 29, 30, 30, 31, 31,
31, 31, 31, 30, 30, 29, 28, 27,
26, 25, 24, 23, 21, 20, 19, 17,
16, 14, 12, 11, 10, 08, 07, 06,
05, 04, 03, 02, 01, 01, 00, 00,
00, 00, 00, 01, 01, 02, 03, 04,
05, 06, 07, 08, 10, 11, 12, 14}

pDuration = pDuration * 114 ' Calculate the duration in approx milliseconds
pFreq = pFreq * cMult ' Calculate the value for the DDS based upon the frequency required
lAccum = 0 ' Reset the accumulator
DACCON0bits_DACEN = 1 ' Enable the DAC
Do ' Create a loop
lAccum = lAccum + pFreq.Long ' Accumulation of the frequency
DACCON1 = CRead8 SineTable[lAccum.Byte2 & $3F] ' Divide output by 65536 and extract the first 6 bits
Dec pDuration ' Decrement the duration counter
If pDuration = 0 Then ' Has the duration reached 0?
DACCON0bits_DACEN = 0 ' Yes. So disable the DAC
ExitProc ' Exit the procedure
EndIf
Loop
EndProc

'-----------------------------------------------------------------------------------------
' Initialise the 5-bit DAC peripheral on a PIC16F1823 device
' Input : None
' Output : None
' Notes : Disables the DAC for now
'
Proc DAC_Init()
DACCON0 = 0b00100100
DACCON1 = 0
ANSELA.0 = 1 ' Make the DAC pin analogue
ANSELA.1 = 1 ' Make the +Vref pin analogue
PinInput PORTA.0 ' Make the DAC pin an input
PinInput PORTA.1 ' Make the +Vref pin an input
EndProc

'-----------------------------------------------------------------------------------------
' Setup the program
' Input : None
' Output : None
' Notes : None
'
Proc Setup()
Osc_16MHz() ' Setup the device to operate at 16Mhz with its internal oscillator
DAC_Init() ' Initialise the DAC
EndProc

'-----------------------------------------------------------------------------------------
' Setup the PIC16F1823 to use the internal oscillator at 16 MHz
' Input : None
' Output : None
' Notes : None
'
Proc Osc_16MHz()
OSCCON = 0b01111010
OSCTUNE = $00
BORCON = $00
EndProc

'-----------------------------------------------------------------------------------------
' Setup the config fuses for the internal oscillator on a PIC16F1823 device
'
Config1 FOSC_INTOSC, WDTE_OFF, MCLRE_ON, CP_OFF, BOREN_OFF
Config2 PLLEN_OFF, LVP_OFF, WRT_OFF, STVREN_OFF