Variable help

TC

Hello all,
First, please excuse my vagueness of my question. I can see what I need to do in my head, but it is hard for me to explain what I am talking about.
I am trying to find a way to change the value of a byte sized variable. I have (4) 2-bit sized values that need to make up that byte sized variable.

For example: value_A (2-bits), value_B (2-bits), value_C (2-bits), value_D (2-bits)

I was thinking of along the lines of using "<<=2" to shift the bits 2 places to the left after each value is loaded, but I don't know how I can load my value without changing what I already loaded into the variable.

I hope this makes sense.

Thank you in advance.

kuroneko

If the source(s) are only 2 bit each then this will do:

e := a << 6 | b << 4 | c << 2 | d

If you can't guarantee 2 bit size then they have to be masked before or after shifting but before the final assembly.

TC

Wonderful!! Thank you very much.

I can guarantee they are 2-bit values.

TC

kuroneko, I am trying to understand what is going on with your help to my problem. I might be over thinking this.

start off with
%00000000
load value_A
%00000011
shift to the left 6 places
%11000000
"OR" Value_B
%11000010
shift to the left 4 places
%00100000
Value_A is gone.

Again, I might be over thinking this.

kuroneko

Shift has a higher priority than binary OR (see datasheet section 6.2), IOW first all << ops are executed then all | ops. It's the same as

e := (a << 6) | (b << 4) | (c << 2) | d

TC

Ah, now I get it. I knew I was over thinking it.

Thank You

JonnyMac

Even though parenthesis are not required, I often use them for clarity. The code snippet in this thread is a really good example of that.

TC

It helped me understand it better.