12Bit ADC with PIC18F2523

[Kuba230]

Hello,
I have code for 10 bit ADC which is normally working with PIC18F2455 and I want to use this code for 12 bit ADC with PIC18F2523.
I changed Define ADC_BITS 10 to ADC_BITS 12, but results are sill 10 Bits.
I using 20 MHz external oscillator.
How to configure this code for 12 bit ADC with PIC18F2523 ?

Thank you


Here is my code:

Define LOADER_USED 1
DEFINE OSC 48

' Define LCD registers and bits
Define LCD_DREG PORTB
Define LCD_DBIT 4
Define LCD_RSREG PORTC
Define LCD_RSBIT 7
Define LCD_EREG PORTC
Define LCD_EBIT 6
DEFINE LCD_BITS 4 ' 4-bit data bus
DEFINE LCD_LINES 2 ' LCD - 2 lines


' Define ADCIN parameters

Define ADC_BITS 12 ' Set number of bits in result
Define ADC_CLOCK 3 ' Set clock source (3=rc)
Define ADC_SAMPLEUS 50 ' Set sampling time in uS


adval var word ' Create adval to store result

TRISA = %11111111 ' Set PORTA to all input
ADCON1 = %00001010 ' Set PORTA analog...
ADCON2 = %10000000 ' ...and right justify result

Pause 500 ' Wait .5 second

loop: ADCIN 0, adval ' Read channel 0 to adval
Lcdout $fe, 1 ' Clear LCD
Lcdout "Value: ", DEC adval ' Display the decimal value
Pause 100 ' Wait .1 second
Goto loop ' Do it forever
End

[richard]

ADCON2 = %10000000 ' ...and right justify result

how many times do we see this totally wrong statement

ADCON2 = %10000000 ' ...and right justify result and set the conversion clock to fosc/2
which is way out of limits for a 48mhz osc and contradicts the define
Define ADC_CLOCK 3 ' Set clock source (3=rc)

why not just
ADCON2.7=1
or
ADCON2 = ADCON2 | %10000000 ' ...and right justify result


other than that i have nothing , never tried a 12 bit adc chip.
you may need to do it manually

[Kuba230]

Hello richard,
I configured my code for 12 Bit AD, now I get 12 Bits results, but it is working only with 4MHz external oscillator.
When I replace extenal oscillator wit 20MHz and DEFINE OSC 20, it is not working, what is wrong?


Define LOADER_USED 1
DEFINE OSC 4

' Define LCD registers and bits
Define LCD_DREG PORTB
Define LCD_DBIT 4
Define LCD_RSREG PORTC
Define LCD_RSBIT 7
Define LCD_EREG PORTC
Define LCD_EBIT 6
DEFINE LCD_BITS 4 ' 4-bit data bus
DEFINE LCD_LINES 2 ' LCD - 2 lines


' Define ADCIN parameters

Define ADC_BITS 12 ' Set number of bits in result
Define ADC_CLOCK 3 ' Set clock source (3=rc)
Define ADC_SAMPLEUS 50 ' Set sampling time in uS


adval var word ' Create adval to store result

advalLow VAR WORD ' make it available to use in PBP
advalHigh VAR WORD ' make it available to use in PBP
advalLow = ADRESL
advalHigh = ADRESH


TRISA = %11111111 ' Set PORTA to all input
ADCON1 = %00001010 ' Set PORTA analog...
ADCON2.7=1 ' ...and right justify result

Pause 500 ' Wait .5 second

loop: ADCIN 0, adval ' Read channel 0 to adval
adval = ADRESL + (ADRESH * 256)
Lcdout $fe, 1 ' Clear LCD
Lcdout "Value: ", DEC adval ' Display the decimal value
Pause 100 ' Wait .1 second
Goto loop ' Do it forever
End

[richard]

in what way does it not work ?
where and what are your config settings

advalLow and advalHigh only need to be bytes

advalLow VAR byte ' make it available to use in PBP
advalHigh VAR byte ' make it available to use in PBP


since ADRESH and ADRESHL are sequential in memory for that chip its possible to save a bit of typing by :-

@my_adresult =ADRESHL
my_adresult var word ext

;.............


ADCIN 0, adval ' Read channel 0 to dummy adval
 adval = my_adresult

[Kuba230]

Ok,
I directly saving the ADRESL and ADRESH register which is used to store the end results of an analog-to-digital conversion (ADC) to results adval and sending LCD. My problem is, the code is working properly only with 4MHz oscillator, when I define 20MHz occillator, the conversion is very slow, waiting few second, when start conversion.
Whay the conversion is fast for 4Mhz oscillator and very slow for 20MHz oscillator

adval = ADRESL + (ADRESH * 256)

and sending LCD

Lcdout $fe, 1 ' Clear LCD
Lcdout "Value: ", DEC adval ' Display the decimal value

[richard]

where and what are your config settings ?

the default osc is 1mhz which may be the problem