How do I check (or set) a group of consecutive bits within a byte?

[HankMcSpank]

I know how to check/set individual bits within a register...but how do I check set a consecutive group of bits within a register.

For example, I want to do the folloiwng...

IF ADC channel 6 is presently selected, then set the ADC channel to ADC channel 7

The problem with the ADC control register (ADCON0), is that there's a bit within it that's forever changing (so it's not a static register), therefore I can't do something along the lines of

if ADCON0 = 011001 then ADCON0 = 011101

because bit 2 could be either a 0 or 1 (depending on when I happen to check, the way the wind blows etc), therefore I actually need to only check/set bits 2, 3 & 4 within that register

How do I do that?!!!

Thanks very much (an no sniggering at the back!)


While I'm here if anyone can offer up a slick way of toggling between two ADC channels (if it helps, I'm using the special event trigger to collect ADC samples) that'd be grand. What I'm trying to achieve is extract magnitude from an arriving AC signal level....but I also want to check a pot too (which goes into another pin), so therefore need to switch ADC channels.

[Charlie]

Sounds like the perfect use for logical AND. You would basically "AND" with 00011100 and it would leave any bit with zeros alone. Unfortunately "AND" does not seem to exist in my version of PBP, other than as a comparitor in an IF THEN statement?
Huh??? This is pretty basic functionality ... not sure why it's not there?

[andywpg]

Sounds like the perfect use for logical AND. You would basically "AND" with 00011100 and it would leave any bit with zeros alone. Unfortunately "AND" does not seem to exist in my version of PBP, other than as a comparitor in an IF THEN statement?
Huh??? This is pretty basic functionality ... not sure why it's not there?

Check page 78 of the PBP3 manual - it talks about 'BITWISE AND' (expressed as '&') which is what I think you are looking for.

I haven't been brave (or dumb?) enough to use it yet, but it seems to be there.

Unless you're not using version 3, in which case, please excuse the interruption.

Andy

[mark_s]

Look in your manual under "Logical operators" AND exist. Also you can use &&

When used as " IF(A and B ) <>= C then take Action" Is a true or false statement.

Myvariable = %11111111 AND %0000000, this will AND the two variables into myvariable

[HankMcSpank]

Thanks guys, since the only difference between ADC channel6 & adc channel 7 is 1 bit, I actually I think i've figured a workaround, something like this...

the code below assumes ADCON0 set as something like 11101 to start with (bit 2-6 set the ADC channel, so this would be ADC channel 7 selected)

if adcon0.2 = 1 then ' if bit 2 is set then ADC Channel must presently be CH7
adccon.2 =0            ' clear bit 2, to set ADC channel to Channel 6
else
adccon0.2 = 1         ' if adcon.2 wasn't set as a '1' then ch6 must have been active therefore now set bit 2 to make AD ch7 active.

I think that should toggle between ADC ch6 & ch7 on successive calls?

[Charlie]

Check page 78 of the PBP3 manual - it talks about 'BITWISE AND' (expressed as '&') which is what I think you are looking for.

I haven't been brave (or dumb?) enough to use it yet, but it seems to be there.

Unless you're not using version 3, in which case, please excuse the interruption.

Andy

I'm using 2.6 and it's not in my manual.

[Charlie]

Mark_S wrote:

Look in your manual under "Logical operators" AND exist. Also you can use &&

When used as " IF(A and B ) <>= C then take Action" Is a true or false statement.

Myvariable = %11111111 AND %0000000, this will AND the two variables into myvariable

My 2.6 manual says the result of this test is true or false. No mention of ANDing variables into another variable. Perhaps you've hit on the first real reason to move to 3.0...

[Ioannis]

Bitwise and Logical are two different things. All versions do support them.

You will use Logical AND or &&, OR or ||, XOR or ^^, ANDNOT, ORNOT, XORNOT in TRUE/FALSE case. If value is 0 then it is treated as FALSE. Any other value is treated as TRU. So, in IF-THEN statement you can check if the values are or are not zero.

Example:

A=2:B=0

IF A AND B THEN C=1

C will be set to 1 if both A and B variables are not zero.

But Bitwise Operators act on each and every bit of the variable using boolean maths.

If you want to isolate bits a variables you want to use the & operand.

If you want to set a bit then | is your operand to use.

Example (from the Book):

B0=B0 & %00000001 'Isolate bit 0 of B0

B0=B0 | %00000001 'Set bit 0 of B0

B0=B0 ^ %00000001 'Reverse state of bit 0 of B0

So Hank, you want to use & in your case.

ADCON0 = ADCON & %00011101

Ioannis

[Charlie]

Can you tell me which "Book" this example is from? I'm happy to be corrected - this is exactly what I was looking for - but It's certainly not in my 2.6 Manual.

[Ioannis]

From 2.4 page 36
From 2.6 page 42

or

From 3.0 pages 70 an 78

Ioannis

[Charlie]

You're absolutely right!

If it's any help to anyone else, when I searched for logical AND, the first instance that came up is on page 43. The proper names for the boolean operations (AND, OR, XOR) are not used on P42.

[HankMcSpank]

Well, hopefully some good has come from my initial problem (which I've now sorted/worked around by other means)...thanks for your input everyone!

[Mike, K8LH]

Hank, does PBP allow you to XOR a bit?

adcon0.2 = adcon0.2 XOR 1

That's pretty much how I would do it BoostC ( adcon0.2 ^= 1 ).

Cheerful regards, Mike

[Ioannis]

This adcon0.2 = adcon0.2 XOR 1 does a logical XOR.

You need bitwise XOR:

adcon0.2 = adcon0.2 ^ 1

Ioannis