Weirdness with 16F1705's eeprom and DAC

[wjsmarine]

Hi Richard,

Thanks for looking into this.

I edited my previous code to match yours and the results are crazy - see both 'scope captures below. RA2 is changing the right steps but is offset by about 700mV.

Only difference to code between the two is altering DAC1CON0 to achieve the change in output pin. I thought I might have a dud PIC so changed it but no difference...

Any ideas?

Cheers,
Bill

[richard]

new code without all the noisy comment

with both outputs driven , from fvr buff2 @2.048v [1.024v got weird results]
the unmentioned feature in data sheet is that out2 is complement of out1 and the gain seems a bit different
ps blue trace is dacout1

#CONFIG ; 16F1705
    __config _CONFIG1, _FOSC_INTOSC & _WDTE_ON & _PWRTE_ON & _MCLRE_ON & _CP_OFF & _BOREN_ON & _CLKOUTEN_OFF
    __config _CONFIG2, _WRT_OFF & _PPS1WAY_OFF & _ZCDDIS_OFF & _PLLEN_OFF & _STVREN_ON & _BORV_LO & _LPBOR_OFF & _LVP_OFF       
#ENDCONFIG


a   var byte                    ' Loop counter. 
b var byte[8]






    DEFINE  OSC 4               ' Adjust to suit design.
    OSCCON  = $68         ' Internal 4MHz osc.




    ANSELA = 0
    ANSELC = 0       


    FVRCON = %10001000         ' Enabled, Vref 2.048V.



    DAC1CON0 = %10111000        ' Vref from FVRb2, DAC1out2 (RA2).  DAC1out1 (RA0).  


    TRISA = 0
  


    
   b[0]=128
   b[1]=192
   b[2]=255
   b[3]=192
   b[4]=128
   b[5]=40
   b[6]=0
   b[7]=40


First:  
    a=7
    while a
    DAC1CON1 = b[a]
    pause 5            ' Let the DMM settle.
    a=a-1
    wend
    goto first              


    end

[wjsmarine]

Yes, same as yours Richard.

As a side note I looked at substituting the 16F1705 with a 16F1614 but it only has out1, again on RA0 so did not proceed.

But out2 for me (1705) continues to have the DAC variation superimposed on a 700mV offset no matter what gain I have (x1,2 or 4). The comlementary/inverted output appears to be an undocumented "feature", may have its uses down the track, although I don't understand why the difference in gain between the two.

I tried an external Vref of 1.2V (LM385) and the waveforms appear stunted - may be due I didn't buffer the ref output - however the offset remains and this is the key problem.

Only when I used Vdd as Vref did the offset disappear but in the intended application I need the 1.024V reference, so Vdd is useless. I can use an external DAC (and get some greater resolution at the same time) but it defeats the purpose of using an all-in-one PIC in the first place, plus the pcb is already done albeit a prototype for my needs so I can hack it to use out1.

I won't waste anyone else's time pursuing this further, it is what it is - warts and all...

Cheers, stay safe,
Bill

[richard]

theres more to than i first thought.
i tried the microchip example in mplabx , guess what both pins are exactly equal and produce the exact predicted output by the datasheet,
we are missing something

#CONFIG ; 16F1705    __config _CONFIG1, _FOSC_INTOSC & _WDTE_ON & _PWRTE_ON & _MCLRE_ON & _CP_OFF & _BOREN_ON & _CLKOUTEN_OFF
    __config _CONFIG2, _WRT_OFF & _PPS1WAY_OFF & _ZCDDIS_OFF & _PLLEN_OFF & _STVREN_ON & _BORV_LO & _LPBOR_OFF & _LVP_OFF	   
#ENDCONFIG


counts   var byte                    ' Loop counter. 






    DEFINE  OSC 4               ' Adjust to suit design.
    OSCCON  = $68         ' Internal 4MHz osc.




    ANSELA = 0
    ANSELC = 0       






' ####### RA2 Sits at 2.277V with RA0 selected and running correctly.
    DAC1CON0 = %10110000        ' Vref from FVRb2, DAC1out2 (RA2).  


   
  


    




First:  
    for counts= 0 to 250
    DAC1CON1 = counts
    pause 5            ' Let the DMM settle.
   next
    goto first              


    end

void main(void){
    // initialize the device
    SYSTEM_Initialize();


    // When using interrupts, you need to set the Global and Peripheral Interrupt Enable bits
    // Use the following macros to:


    // Enable the Global Interrupts
    //INTERRUPT_GlobalInterruptEnable();


    // Enable the Peripheral Interrupts
    //INTERRUPT_PeripheralInterruptEnable();


    // Disable the Global Interrupts
    //INTERRUPT_GlobalInterruptDisable();


    // Disable the Peripheral Interrupts
    //INTERRUPT_PeripheralInterruptDisable();
 uint8_t count=0;


    
    while (1)
    {
                for(count=0; count<=250; count++)
        {
            DAC_SetOutput(count);
            __delay_ms(5);


        }
    }
}
/**
 End of File

void DAC_Initialize(void)
{
    // DAC1EN enabled; DAC1NSS VSS; DAC1PSS VDD; DAC1OE1 enabled; DAC1OE2 enabled; 
    DAC1CON0 = 0xB0;
    // DAC1R 51; 
    DAC1CON1 = 0x33;
}


void DAC_SetOutput(uint8_t inputData)
{
    DAC1CON1  = inputData;
}


uint8_t DAC_GetOutput(void)
{
    return DAC1CON1;
}


// CONFIG1
#pragma config FOSC = INTOSC    // Oscillator Selection Bits->INTOSC oscillator: I/O function on CLKIN pin
#pragma config WDTE = OFF    // Watchdog Timer Enable->WDT disabled
#pragma config PWRTE = OFF    // Power-up Timer Enable->PWRT disabled
#pragma config MCLRE = ON    // MCLR Pin Function Select->MCLR/VPP pin function is MCLR
#pragma config CP = OFF    // Flash Program Memory Code Protection->Program memory code protection is disabled
#pragma config BOREN = ON    // Brown-out Reset Enable->Brown-out Reset enabled
#pragma config CLKOUTEN = OFF    // Clock Out Enable->CLKOUT function is disabled. I/O or oscillator function on the CLKOUT pin
#pragma config IESO = ON    // Internal/External Switchover Mode->Internal/External Switchover Mode is enabled
#pragma config FCMEN = ON    // Fail-Safe Clock Monitor Enable->Fail-Safe Clock Monitor is enabled


// CONFIG2
#pragma config WRT = OFF    // Flash Memory Self-Write Protection->Write protection off
#pragma config PPS1WAY = ON    // Peripheral Pin Select one-way control->The PPSLOCK bit cannot be cleared once it is set by software
#pragma config ZCDDIS = ON    // Zero-cross detect disable->Zero-cross detect circuit is disabled at POR  the culprit
#pragma config PLLEN = OFF    // Phase Lock Loop enable->4x PLL is enabled when software sets the SPLLEN bit
#pragma config STVREN = ON    // Stack Overflow/Underflow Reset Enable->Stack Overflow or Underflow will cause a Reset
#pragma config BORV = LO    // Brown-out Reset Voltage Selection->Brown-out Reset Voltage (Vbor), low trip point selected.
#pragma config LPBOR = OFF    // Low-Power Brown Out Reset->Low-Power BOR is disabled
#pragma config LVP = ON    // Low-Voltage Programming Enable->Low-voltage programming enabled




void PIN_MANAGER_Initialize(void)
{
    /**
    LATx registers
    */
    LATA = 0x00;
    LATC = 0x00;


    /**
    TRISx registers
    */
    TRISA = 0x37;
    TRISC = 0x3F;


    /**
    ANSELx registers
    */
    ANSELC = 0x3F;
    ANSELA = 0;//0x17;


    /**
    WPUx registers
    */
    WPUA = 0x00;
    WPUC = 0x00;
    OPTION_REGbits.nWPUEN = 1;


    /**
    ODx registers
    */
    ODCONA = 0x00;
    ODCONC = 0x00;


    /**
    SLRCONx registers
    */
    SLRCONA = 0x37;
    SLRCONC = 0x3F;


    /**
    INLVLx registers
    */
    INLVLA = 0x3F;
    INLVLC = 0x3F;










   
    
}
  
void SYSTEM_Initialize(void)
{


    PIN_MANAGER_Initialize();
    OSCILLATOR_Initialize();
    WDT_Initialize();
    DAC_Initialize();
}


void OSCILLATOR_Initialize(void)
{
    // SCS FOSC; SPLLEN disabled; IRCF 4MHz_HF; 
    OSCCON = 0x68;
    // SOSCR disabled; 
    OSCSTAT = 0x00;
    // TUN 0; 
    OSCTUNE = 0x00;
    // SBOREN disabled; BORFS disabled; 
    BORCON = 0x00;
}


void WDT_Initialize(void)
{
    // WDTPS 1:65536; SWDTEN OFF; 
    WDTCON = 0x16;
}

[richard]

found it

config use _ZCDDIS_ON

#CONFIG ; 16F1705    __config _CONFIG1, _FOSC_INTOSC & _WDTE_ON & _PWRTE_ON & _MCLRE_ON & _CP_OFF & _BOREN_ON & _CLKOUTEN_OFF
    __config _CONFIG2, _WRT_OFF & _PPS1WAY_OFF & _ZCDDIS_ON & _PLLEN_OFF & _STVREN_ON & _BORV_LO & _LPBOR_OFF & _LVP_OFF	   
#ENDCONFIG


counts   var byte                    ' Loop counter. 






    DEFINE  OSC 4               ' Adjust to suit design.
    OSCCON  = $68         ' Internal 4MHz osc.
   
    ANSELA = 0
    ANSELC = 0       
     




    DAC1CON0 = %10110000        ' Vref from vdd, DAC1out2 (RA2).  DAC1out1 (RA0). 


   
  


    




First:  
    for counts= 0 to 250
    DAC1CON1 = counts
    pause 5           
   next
    goto first              


    end

[wjsmarine]

Woohoo! I just confirmed it with my 'scope.

You are the man Richard. Put a star up against your name mate!

Thanks again for your help, appreciated.

Kind regards,
Bill