Bit test or -flag test in spin

gwkaub · 2014-04-28 17:37

Ok this has me lost; working in spin can I check a bit or negative flag ?
I'm trying to send out long & short pulses (IR code) I call dash & dot.
Sending out high bit first 16 bits. I first need to check 1 or 0, being high bit I could check -flag.
This is the code giving me problem:

pub aux
t1 := 1600 'dash 1.6 ms
t2 := 750 'dot 750 µs
strobe(46500) 'sync pulse 9.3 ms
waitcnt(22000 + cnt) '4.4 MS
strobe(3500) '700 µs
waitcnt(2000 + cnt) '400 µs
start := $08ff
repeat 16
if start and $8000 'high bit 1
dash
else
dot
strobe(2500)
start <<= 1 'shift left for next bit
repeat 16
if code and $8000 'high bit 1
dash
else
dot
strobe(2500)
code <<= 1 'shift left for next bit

T Chap · 2014-04-28 17:42

Hello and welcome! You can present your code a little better if you add [ code ] to the top of the code and [ / code ] at the bottom. Remove the spaces.

As an example, are you trying to say

If X & Y == 1 ?

JonnyMac · 2014-04-28 17:44

You should use the [ code ] [ /code ] tags (witout the spaces) -- will make your code easier to read.

You can test a bit by using a mask.

if (testvalue & (1 << 7))
    ' bit7 of testvalue is set

Make sure you're using & to test bits, not and (which is a logical test)

gwkaub · 2014-04-28 18:58

Ok I should have said this is my object called aux . I first send $08ff "start" 16 bits, this is same all keys.
Then I send 16 bit code for key pressed.

pub aux
t1 := 1600 'dash 1.6 ms
t2 := 750 'dot 750 µs
strobe(46500) 'sync paulse 9.3 ms
waitcnt(22000 + cnt) '4.4 MS
strobe(3500) '700 µs
waitcnt(2000 + cnt) '400 µs
start := $08ff
repeat 16
if start & $8000 'high bit 1
dash
else
dot
strobe(2500)
start <<= 1 'shift left for next bit
repeat 16
if code & $8000 'high bit 1
dash
else
dot
strobe(2500)
code <<= 1 'shift left for next bit

T Chap · 2014-04-28 19:02

Can you please format the code with the [ code ] at the beginning of your code and [ /code ] at the bottom of the code so that is appears with the correct indentation? Remove the spaces from the brackets.

gwkaub · 2014-04-28 19:15

New to this; now I get it !

    
pub aux
  t1 := 1600                    'dash 1.6 ms
  t2 := 750                     'dot 750 µs
  strobe(46500)                 'sync pulse 9.3 ms
  waitcnt(22000 + cnt)          '4.4 MS
  strobe(3500)                  '700 µs
  waitcnt(2000 + cnt)           '400 µs
  start := $08ff
  repeat 16
    if start and $8000          'high bit 1
     dash
    else 
     dot
    strobe(2500)                 
    start <<= 1                 'shift left for next bit
  repeat 16
    if code and $8000           'high bit 1
     dash
    else 
     dot
    strobe(2500)                 
    code <<= 1                 'shift left for next bit

T Chap · 2014-04-28 19:17

if start and $8000 must be if start & $8000

if code and $8000 must be if code & $8000

AND is used in a case where you want to test two or more things:

If X > Y AND if Y > Z then
do something.

The manual will have the examples for AND and &.

JonnyMac · 2014-04-28 19:28

There is a difference between bitwise and (&) and logical and (and) -- you are using the wrong one.

You have redundant elements in your code; you can use this method to send any 16-bit value (start or the code).

pub sendit(value)

  repeat 16
    if (value & $8000)
      dash
    else
      dot
    strobe(2500)
    value <<= 1

Note the use of bitwise and (&) with the mask so the if expression will only evaluate as true when value.bit15 is one. When using logical and, any non-zero value is promoted to true; this is not what you want when testing specific bits.

Bit test or -flag test in spin

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