ADC port contradictions

caddy · Joined: 24 Jun 2007 Posts: 14

Hi

I'm using an 18F2525 with 12 ADC ports. In the datasheet it says:

dyeatman · Joined: 06 Sep 2003 Posts: 1933 Location: Norman, OK

You might read the data sheet again. The 18F2525 is a 28 pin device and has 10 ADC channels. (AN5-AN7 are not available)

Page 224 of the data sheet shows all the possible Analog port configurations. The datasheet does not show an option to configure just AN8 and AN9. The compiler is limited by what the hardware will do.

Also, which CCS version are you using? The ADC definitions in my header file (ver 4.042) differ greatly from yours. (don't get confused between A5 and AN5, one is a pin and the other is the ADC port)

// Constants used in SETUP_ADC_PORTS() are:
#define NO_ANALOGS 0x0F // None
#define ALL_ANALOG 0x00 // A0 A1 A2 A3 A5 B2 B3 B1 B4 B0
#define AN0_TO_AN11 0x03 // A0 A1 A2 A3 A5 B2 B3 B1 B4
#define AN0_TO_AN10 0x04 // A0 A1 A2 A3 A5 B2 B3 B1
#define AN0_TO_AN9 0x05 // A0 A1 A2 A3 A5 B2 B3
#define AN0_TO_AN8 0x06 // A0 A1 A2 A3 A5 B2
#define AN0_TO_AN4 0x0A // A0 A1 A2 A3 A5
#define AN0_TO_AN3 0x0B // A0 A1 A2 A3
#define AN0_TO_AN2 0x0C // A0 A1 A2
#define AN0_TO_AN1 0x0D // A0 A1
#define AN0 0x0E // A0

Guest · Posted: Sun Jun 24, 2007 3:28 pm

Thanks

What if I se up all ports as analog just before using the adc, and then set them back to digital when using the digital ports. As long as I leave a delay between the setup and conversion to allow it to initialise there shouldnt be a problem right??

dyeatman · Joined: 06 Sep 2003 Posts: 1933 Location: Norman, OK

Thats a good question someone here might be able to answer. I have never tried that trick. I have always just used the ports I needed starting from AN0 in the normal configurations....

After doing some more investigation it appears some unused Analog pins can be configured as digital OUTPUT only (ex: RA0 and RA1). The D/S says they cannot be configured for digital input when Analog is enabled. Again, I have never tried this. I am getting this from reading the data sheet.

caddy · Joined: 24 Jun 2007 Posts: 14

Well, they wouldn't need to be analog and digital simultaneously. The code I'm thinking of would be something like:

jfk1965 · Joined: 21 Oct 2003 Posts: 58

why not just use A0 & A1 as Analog as the others as digital and you don't have to switch from analog to digital and back again?

caddy · Joined: 24 Jun 2007 Posts: 14