Accessing Individual bits within a byte

Branmuffin Industries

I am trying to overwrite the four low bits in a byte while leaving the four high bits alone. it used to be, with the basic stamp, we could individually address the bits of a byte with the .bit[noparse][[/noparse]0] command. Since we can no longer do that, does anyone have an idea for a workaround?

Ryan Brandys

OzStamp

Hi

In Spin or ASM just some quick pointers..explore further from there

Spin
old : = old & new

ASM 'setting bits to zero
and old, new 'new..zero for overwriting to zero just alter the 4 lsb bits..

ASM 'setting bits to one
or old,new



Rgds Ron Mel oz

Paul Baker

Yeah in spin it would look something like:

a := a & $F0 | b & $0F

this replaces the lower 4 bits in a with the lower 4 bits in b.

I see Ron beat me to it, I agree with his advice.

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Paul Baker
Propeller Applications Engineer

Parallax, Inc.

Branmuffin Industries

Thanks, guys! I am now doing some really cool specific overwrites of individual bits within a byte. check out my code:

PUB Scanning( _Pack ) | counter, pos, addme , eraser

pos := 1

repeat counter from 0 to 16

if _Pack == LeftPack
eraser := %1010_1010_1111_1111
if pos == 1
pos := 2
addme := %0000_0001_0000_0000
elseif pos == 2
pos := 3
addme := %0000_0100_0000_0000
elseif pos == 3
pos := 4
addme := %0001_0000_0000_0000
elseif pos == 4
pos := 1
addme := %0100_0000_0000_0000
else
eraser := %1111_1111_1010_1010
if pos == 1
pos := 2
addme := %0000_0000_0000_0001
elseif pos == 2
pos := 3
addme := %0000_0000_0000_0100
elseif pos == 3
pos := 4
addme := %0000_0000_0001_0000
elseif pos == 4
pos := 1
addme := %0000_0000_0100_0000

BattState := BattState & eraser
BattState := BattState | addme
WriteLEDS 'update LED array
waitcnt( 9_000_000 + cnt)

Beau Schwabe

Branmuffin Industries,

If I understand the code that you posted corectly, you might be able to simplify it down to this...

PUB Scanning( _Pack ) | counter, pos, addme , eraser 
    pos := 0
    repeat counter from 0 to 16 
      if _Pack == LeftPack
         eraser := %1010_1010_1111_1111 
         addme := %0000_0001_0000_0000
      else
         eraser := %1111_1111_1010_1010 
         addme := %0000_0000_0000_0001 
      addme <<= (pos*2)
      pos += 1
      pos &= %11
      BattState &= eraser
      BattState |= addme 
      WriteLEDS 'update LED array
      waitcnt( 9_000_000 + cnt)
[url=http://forums.parallax.com/member.php?u=49994][/url] 

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.