Question

I need to count from 0 to 10 and store those values in binary format in ADCON0(5:2). How do I point at bit 5 of this register? Bit 5 is named ADCON0bits.CHS3. If I store a 4 bit variable to ADCON0bits.CHS3, will bits 1 – 3 be written to bits 4 – 2 of the register?

Also, are there any 4 bit data types that I could use?

This is all on a PIC microcontroller.

Edit: I need to store 4 bits in the register like so:

unsigned char count = 10 //max value
[X][X][1][0][1][0][X][X]

This is in line with what was assumed below, but I figured I would clear up my question a bit.

Answer 1

Writing to a bit variable stores the truth value of that variable to the bit. For example, writing:

ADCON0bits.CHS3 = 3;

will set that bit to 1.

If bit5 refers to the bit masked by 0x20 (00100000) and you need to store the 4 bit number in bits masked 0x3c (00111100) then you can use bit shifts and bitwise operations:

// First clear bits 1-5:
ADCON0 &= ~0x3c;

// Now set the bits to correct value:
ADCON0 |= (count << 2); // <-- remember to shift 2 bits to the left

update: As mentioned by Ian in the comments. This sets ADCON0 to an intermediate value before updating. In this case it is OK since it is only selecting the A/D channel and not actually executing the conversion. But in general it’s better to do:

unsigned char temp_adcon;

temp_adcon = ADCON0 & ~0x3c;
ADCON0 = temp_adcon | (count << 2);