Reading bits

agimuhing

How do you read the individual bits of a byte, word, or long?

Cluso99

It depends on what you are trying to do, and also if you are using spin or pasm.
If you are getting input from the pins, check the spin ina instruction - it can extract certain bits and put them into the lower bits.
You can perform an "and" to extract the required bits.
In pasm we can use the test instruction, or rotate into the carry position and use the carry if_c option.

So, you need to describe what you are trying to achieve.

agimuhing

I want to make a serial communication object
I need it to be fast for what I'm planning to use it for (too difficult to describe, but it involves USB) so most of it will be in pasm

I know how to extract bits but I'm wondering if there is any special assembly instruction that can do this

JonnyMac

As Clusso pointed out, you can use the C flag in PASM. To give you an example, I wrote this code that sends 16 bits to a DAC. The value is passed to the routine as 16 bits. The first thing the subroutine does is shift it left to move bit15 to bit31. Inside the loop a rotate instruction moves the bit31 into the C flag which is used to control the output.

setdac                  shl     aout, #16                       ' move bit15 to bit31
                        mov     tmp1, #16                       ' shift 16 bits

                        andn    outa, smask                     ' sync low

:loop                   rcl     aout, #1                wc      ' move bit (MSB) to C
                        muxc    outa, dmask                     ' move C to DIN pin
                        andn    outa, cmask                     ' clock low
                        or      outa, cmask                     ' clock high
                        djnz    tmp1, #:loop                    ' more bits?

                        or      outa, smask                     ' sync high

setdac_ret              ret