Beginner in need of help !!

[robbo78]

Hi Tabsoft, thanks a lot for your help I appreciate it. I will go back through everything you have stated & set it up right this time. I did think there were other bits to change but didnt want to mess as I didnt know what I was doing, but ai should now with your info.

Thanks again, I will let you know how it goes.
Rob

[Tabsoft]

Rob,

One correction in my earlier post.

The CVref calculation for High Range is CVREF = (VDD/4) + (VR3:VR0 X VDD/32).
Using your input values of VDD=3.3 and VR3:VR0=8, the calculation will come out like this.
(3.3/4) + (8 x (3.3/32) = (0.825) + (8 x 0.103125) = (0.825) + (0.825) = 1.65 Vdc

If you use Low Range then here is the info:
CVREF = (VR3:VR0/24) x VDD = (8/24) x 3.3 = 0.333 x 3.3 = 1.1 Vdc

Regards,

[robbo78]

Hi Tabsoft,

Right I have changed the bits in the VRCON to the right stuff, so I think that is right now. I did change bits in the CMCON0 but none of it seemed to make a difference, so I have put it back to how it was. I'm thinking either I'm testing the wrong bit still or my actual hardware setup is wrong.

Maybe you can point something out?

BTW I am using the low range Also this is correct - As I understand you want to check the input pin voltage against your "1.1" reference you are setting up internally and have the following outcomes: If the input is "Lower than 1.075 Vdc" you want the LED to be OFF and you want the LED to be "ON when the input is Higher than 1.075 Vdc".

Code -

'PIC 12F683


#CONFIG 
   __config _INTRC_OSC_NOCLKOUT & _WDT_OFF & _MCLRE_OFF & _CP_OFF
#ENDCONFIG


DEFINE OSC 4 '4mhz ocsillator
ANSEL = %00000010 'pin 6 analog
CMCON0 = %00000100 'comparator mode
VRCON = %10101000 'voltage reference
TRISIO = %00000010 'pin 6 input


POT1 VAR CMCON0.2 'pot pin 6
LED VAR GPIO.2 'led pin 5


PAUSE 20


main:
IF POT1 = 1 THEN 
HIGH LED
ELSE
LOW LED
ENDIF
GOTO main

Thanks again,
Rob

[Tabsoft]

Rob,

Yes you're not testing the correct bit for the actual output of the Comparator..

Look at my post again where I listed the things you need to correct. Look at item 2.
I point you to where you can find the answer of which bit in which register to test.
I also point you to where you can determine what the output of the comparator will be for different configurations and physical connections.

Have a read of this info again, I'm sure you'll get it.

Regards

[robbo78]

Hi Tabsoft, okay had another read at first it was just going over my head. Am I right in saying I need to read bit 6 of CMCON0? So CMCON0.6?

Thanks,
Rob

[Tabsoft]

Exactly!

CMCON0 Register:
bit 6 COUT: Comparator Output bit.
This is the logic bit output of the Comparator.

CM: Comparator Mode = 100


With this setup the comparator is comparing VIN- (CIN-/GP1) to VIN+ (which is not an external pin but it is "From CVREF Module", internal voltage reference)
So you need to look at the description of COUT in the CMCON0 register listed below AND you need to look at Table 8-1 in the DS.
This will help you work out what value CMCON0.6 will be based upon a given input on GP1.
Take note that CINV is a configuration bit within the CMCON0 register that determines the logic polarity of COUT.

COUT: Possible values
When CINV = 0:
1 = VIN+ > VIN-
0 = VIN+ < VIN

When CINV = 1:
1 = VIN+ < VIN-
0 = VIN+ > VIN

[robbo78]

Brilliant! Thanks for the info again your the best! I should be able to get this working how I want it to now, then & only then will I move onto interupt with it.

Thanks again,
Rob