SILLION BUG issue on ADC and get around required 16F1947 rev 2 silicon

[longpole001]

WEll , another day, another bug

This one stems from what i think is a result of sillion issue with the ADC

Chip is a 16F1947 Rev 2 device ID is shown as 2522

The erratica from microchip tells of a ADC problem under some conditions , from what i am seeing is under most conditions and it hangs the cpu

http://ww1.microchip.com/downloads/e...Doc/80497F.pdf

The code has worked fine on other chips ( 16f1825, 16F1829 ,) and does work ok on this one when it does not hang the chip


Typically the chip hangs ranging form 1 min to to 20mins , but the code functions as it should during that time

i confirmed this part of the code by not doing the ADcin command and setting the "Value" variable = to a set number with no other changes and no cpu occured - tested for over 1 hour

Unfortunately i dont have another silicon revision to confirm my thoughts , but a workable get around would confirm the issue

Microchip tells of 2 workarounds , ...

1. is change to dedicated RC oscillator - not an option - when using the internal osc
2. Provide a fixed delay in software to stop the A-to-D conversion manually, after all ten bits are
converted, but before the conversion would complete automatically

Option 2 means that the command of ADCIN cant be used ?? and need to be a set register , counter and flag approch , which i not done for
ADC, so some input on this would be helpful.

snippets of code as it relate to the ADC as follows

regards

Sheldon
my internal is 32Mhz

    DEFINE ADC_BITS 10            ' Number of bits in ADCIN result - Required for adcin command 
    DEFINE ADC_SAMPLEUS 10    ' ADC sampling time in microseconds - Required for adcin command 

' ------------ADC Settings , routines and Variables ----------------
  ADCON0 =  %00010001           ' bit 7 -N/A , Bit 6-2 = ADC chan Sel /Temperature output /FVR output = AN4 sel = 00100 ,
                                            ' Bit 1 - Go/_done status flag - 1 = Go do ADC / 0 = Done ADC , Bit 0 = Enable ADC = 1  / 0 = Disable ADC
  
  ADCON1 =  %11110000           ' bit 7 = 1 ADFM ( ADRESH, ADRESL - right justify ).Bit 6-4 ADCS = 111 - using FRC internal ( 1.6us per sample) 
                                            ' Bit3 - N/A , Bit2 = 0 (Vref- is connected to Vss) , Bit1-0 = 00 - Vref+ connected to VDD 
  
  FVRCON  = %00000010           ' Bit 7 =0 disable Fixed Voltage Ref Modual, Bit 6 = VRef ready bit =1 always ok on 16F1825, Bit 5 - Temp indicator 1= enable/0 = disable
                                ' Bit 4 = Temp Indicator Range Sel 0=Vout -Low range / 1= Vout -High range , Bit 3-2 = 00( DAC Fixed volt sel )
                                ' Bit 1-0 = 10 - ADC Fixed Vref of 2.048v   
  
  AvgCount	    CON  10		    ' Number of samples to average in Average routine
  Fastspread	CON  200	    ' Fast Average threshold +/-  in Average routine
  ADavg	    	VAR  WORD       ' Accumulated Varable of Readings in Average routine
  Value	    	VAR  WORD       ' Temp varable assigned in Average routine

' ----------------------------------------------------------------------------------------


   y = 0                          ' ensure 0
  While Y < 10                    ' do 10 voltage reads
    ADCIN 4 ,Value                ' Read PortA.5 value into variable , this applies the fixed voltage ref (via ADCON0,ADCON1,FVRCON)
                                        ' to comparitor and ADC pin selected and gives result.    
    gosub Average                ' Go do running average of ADC reading
    y = y+1                        ' Increment loop counter
  wend  



' -=-=-=-=-=-=  Average Analog values - a DT routine -=-=-=-=-=-=-=-=-=-=
Average:
    IF Value = ADavg Then NoChange
    IF ABS (Value - ADavg) > Fastspread OR Value < AvgCount Then FastAvg
    IF ABS (Value - ADavg) < AvgCount Then RealClose
    ADavg = ADavg - (ADavg/AvgCount)
    ADavg = ADavg + (Value/AvgCount)
    GoTo AVGok
  FastAvg:
    ADavg = Value
    GoTo AVGok
  RealClose:
    ADavg = ADavg - (ADavg/(AvgCount/4))
    ADavg = ADavg + (Value/(AvgCount/4))
  AVGok:
    Value = ADavg			' Put Average back into Value
  NoChange:
Return

[longpole001]

by setting the ADC command enable / disable at the beginning / end of the subrouting which has the adcin command , the hanging is not as often but its there still

[towlerg]

Wow, what a ballsie guy. If I saw anything from from Microchip even hinting at such a problem, I'd drop that PIC so fast.

[longpole001]

well i next time ill ask the chip supplier for rev3 or better , but like most supplier its is very rare they actually supply details of the silicon ver with chip supplied details

[Amoque]

I think chips are like children in that once you own them you have to work with what you have... Certainly abandoning one to start again with another is, except under the rarest circumstances, a difficult choice.





While many of you do not share the holiday, I wish for you all the blessings we in the US celebrate this Thanksgiving season.

[longpole001]

rereading the methods to get around the problem option 1 actully looks the best way , but i am not sure how to do this

but it appears that by setting the ADC f/OSC conversion clock to the FRC internal , then putting the CPU into low power mode ( SLEEP mode ) , then doing a sample , then exit low power mode (SLEEP mode) by using the watchdog timer ( no other way i can see to make sleep mode exit)

i am guessing this may work but not sure ,

1. set up watchdog timer to be enabled by software bit ( _WDTE_SWDTEN ) ;WDT controlled by the SWDTEN bit in the WDTCON register) in config1 word
2. set WDTCON with 1ms timeout and enable watchdog timer lowest time
3. do asm command of sleep - to enter low power mode ( NAP 0 = too long a time about 18ms)
4. do adcin command which should complete a sample in 1.6uS
5.turn off watchdog timer

so the assumption is that the adcin command will work in low power mode and sample will complete in a max of 1ms

test to see !!!!!!!!!!!!

but anyone else can advise then please do

Cheers sheldon


item 1

' config for 16F1947
    #CONFIG
;----- CONFIG1 Options --------------------------------------------------
    __config _CONFIG1, _FOSC_INTOSC & _WDTE_SWDTEN & _PWRTE_ON & _MCLRE_ON & _CP_OFF & _CPD_OFF & _BOREN_OFF & _CLKOUTEN_OFF & _IESO_OFF & _FCMEN_OFF


;----- CONFIG2 Options --------------------------------------------------
    __config _CONFIG2, _LVP_OFF & _BORV_HI & _STVREN_ON & _PLLEN_ON & _WRT_OFF & _VCAPEN_OFF 
    #ENDCONFIG

item 2 - 5

  ADCON0 =  %00010001           ' enable ADC AN4 , ADCON1 setup at start of program 
   
   y = 0                          ' ensure 0
  While Y < 10                    ' do 10 voltage reads
                                  ' silicon bug in rev2 of 16F1947 , requires ADC to be done in lowpower mode and with FDC osc clock internal
    WDTCON = %00000001            ' start watchdog timer set for 1ms so that sleep mode is exit after doing adcin commands
    asm
     SLEEP                        ;'Put cpu into low power mode  
    endasm
    ADCIN 4 ,Value                 ' Read PortA.5 value into variable , this applies the fixed voltage ref (via ADCON0,ADCON1,FVRCON)
    WDTCON = %00000000             ' stop  watchdog timer after  adcin commands
    gosub Average                  ' Go do running average of ADC reading
    y = y+1                        ' Increment loop counter
  wend

[Darrel Taylor]

That won't work, since it will have to wake from sleep before running the ADCIN command.

I might suggest something like this...
It doesn't work in the simulator, but hopefully it will work on real hardware.

It uses the ADIF interrupt to wake from sleep. With the FRC clock, it only takes 48uS to complete a conversion.
Waiting for the WDT is going to take 1000uS or more.
The WDT is enabled just in case the conversion doesn't complete, but the ADIF should always wake it up first.

It assumes you are using other interrupts, and disables them accordingly.

#CONFIG
    __config  _CONFIG1, _FOSC_INTOSC & _WDTE_ON & _PWRTE_OFF & _MCLRE_ON & _CP_OFF & _CPD_OFF & _BOREN_ON & _CLKOUTEN_OFF & _IESO_ON & _FCMEN_ON
    __config  _CONFIG2, _WRT_OFF & _PLLEN_ON & _STVREN_ON & _BORV_19 & _LVP_OFF
#ENDCONFIG
OSCCON = %11110000           ; 32Mhz Internal

DEFINE HSER_RCSTA 90h        ' Enable serial port & continuous receive
DEFINE HSER_TXSTA 20h        ' Enable transmit, BRGH = 0
DEFINE HSER_SPBRG 25         ' 19200 Baud @ 32MHz, 0.16%
DEFINE HSER_CLROERR 1        ' Clear overflow automatically

ADON      VAR ADCON0.0       ; A/D converter Enable
GoDone    VAR ADCON0.1       ; A/D conversion in progress
ADIE      VAR PIE1.6         ; A/D Interrupt Enable
ADIF      VAR PIR1.6         ; A/D Interrupt Flag
GIE       VAR INTCON.7       ; Global Interrupt Enable
GIEsave   VAR BIT            ; Saves state of GIE

ADchan    VAR BYTE           ; Current A/D channel
ADvalue   VAR WORD           ; A/D result

ADCON1 = %10110000           ; Right Justify, FRC clock
ADON = 1

Main:
    FOR ADchan = 0 TO 16     ; Loop through all A/D channe
        ADCON0 = (ADCON0 & %11) | (ADchan << 2) ; Set Analog Channel
        PAUSEUS 20           ; Acquisition time
        GIEsave = GIE        ; Save state of Global Interrupts
        GIE = 0              ; Disable Global interrupts
        ADON = 0             ; reset A/D module
        ADON = 1
        ADIF = 0             ; Clear Analog Interrupt Flag
        ADIE = 1             ; Enable Analog Interrupt
        GoDone = 1           ; Start Analog conversion
        @ SLEEP              ; go to SLEEP
        ADIE = 0             ; Disable Analog Interrupt
        GIE = GIEsave        ; Restore Global Interrupt state
        ADvalue.HighByte = ADRESH  ; Get A/D result
        ADvalue.LowByte  = ADRESL

        HSEROUT [DEC2 ADchan," = ",DEC ADvalue,13,10]
        PAUSE 200
    NEXT ADchan
GOTO Main

[longpole001]

thanks Darrel,


I have put this code in for the AN4 sensor only , however it seems i will have to do this for other A/D services for this rev of chip ????


your DT_INTS-14.bas is included as part of this code for timer0 , and the variable GIE was already in use ,

timer0 setup as 8ms timer , and this A/D routine is called from it after incrementing counters of timer0 = 5sec duration to do a read of the Voltage level


couple of questions
1. Is the duration of the sample time of 20us seemed long for 1 A/D channel ? as the spec sheet for conversion using FRC is about 1.6us average - a max period of 6uS
2. i thought the sleep instruction ( low power mode ) may need to be issued prior to the conversion starting , or are all commands after a sleep command not actioned till sleep mode is terminated ?
3. as this now monitors the interrupt for sleep to finish , then the duration of this routine must be shorter than any other generated interrupts using DT_INT14 else this will not work ??



the code as it stands now
waiting on a Battery power duration test to complete to see if this works ok

Cheers

Sheldon

Get_volts :
   ADON      VAR ADCON0.0         ; A/D converter Enable
   GoDone    VAR ADCON0.1         ; A/D conversion in progress 
   ADIE      VAR PIE1.6           ; A/D Interrupt Enable
   ADIF      VAR PIR1.6           ; A/D Interrupt Flag
   GIEsave   VAR BIT              ; Saves state of GIE

    
    ADCON0 =  %00010001           ' enable ADC AN4 ,( ADCON1 setup at start of program  , Right Justify, FRC clock  )
   
   y = 0                          ' ensure 0
  While Y < 10                    ' do 10 voltage reads
                                  ' silicon bug in rev2 of 16F1947 , requires ADC to be done in lowpower mode and with FDC osc clock internal 
                                  ' also ADCIN command wont work in sleep mode , interupts exit sleep mode  
        PAUSEUS 20                ; Acquisition time
        GIEsave = GIE             ; Save state of Global Interrupts  ( GIE defined in DT_INTS-14.bas )
        GIE = 0                   ; Disable Global interrupts
        ADON = 0                  ; reset A/D module
        ADON = 1                  ; turn on A/D module
        ADIF = 0                  ; Clear Analog Interrupt Flag
        ADIE = 1                  ; Enable Analog Interrupt
        GoDone = 1                ; Start Analog conversion
        @ SLEEP                   ; go to SLEEP
        ADIE = 0                  ; Disable Analog Interrupt
        GIE = GIEsave             ; Restore Global Interrupt state  ( GIE defined in DT_INTS-14.bas )
        value.HighByte = ADRESH   ; Get A/D result
        value.LowByte  = ADRESL         
           
       ' ADCIN 4 ,Value           ' Leave out for Rev 2 of 16F1947 - Read PortA.5 value into variable , this applies the fixed voltage ref (via ADCON0,ADCON1,FVRCON)
        gosub Average             ' Go do running average of ADC reading
        y = y+1                   ' Increment loop counter
  wend

[Darrel Taylor]

1) If you are only reading 1 channel, you don't need any acquisition time.

2) When you put a PIC to SLEEP, all program execution STOPS.
Some peripherals may continue to operate, but the program will not run again until it wakes up.

3) When you put a PIC to SLEEP, the main oscillator is shut-down.
If you are running TIMER0 from the system clock, it too stops during sleep, and your 8mS periods will be extended.

[longpole001]

thanks darrel ,

ill let you know how it goes for testing in 24 hours

Well i wish had known of issues with this chip prior , will make an effort to check every time now for microchips erratica on each chip before using
oh well , it seems this problem is only with the silicon ver 2 , i hope the supplier can help me with higher revisions exchanged , cos this is dog of a version


cheers

Sheldon

[longpole001]

seems to be workin , cheers darrel