> Van: PHXSYS <PHXSYS@AOL.COM>
> Aan: PICLIST@MITVMA.MIT.EDU
> Onderwerp: Whats the difference between IF true and NOT
> Datum: vrijdag 8 mei 1998 5:59
>
> Hello
>
> According to the stamp manual page 274, if I understand it you can write
an
> If...then statement like:
>
> Flag     var    byte
> Flag  =  1
>
> If flag then  istrue          'Value is true- True is any value other
than 0
>      and
> If NOT flag then istrue    'Is also true
>
> Isn't NOT 1 the same as 0 or 2...any non 0 number. If true is any value
other
> than 0 and "NOT 1 is true" as well as any non-zero numberI don't
understand
> the difference.
>
> For example whats the difference between these two commands
>
> IF NOT in1 then si2c_rbyte_dl
>     and
> IF bit_count then si2c_rbyte_lp
>
>
> Thanks
>
> Jon

Try to look at it this way :

True & False are _logical_ variables (1 Bit wide). You can represent them
as you like, as is done here : 0 == True, all other values are False.  So,
first convert your register-value (256 states, 0 thru 255) to a Logical
state (2 states, True or False)

Now let's look at your question :

  if <var> then <action>

If <var> is 0 it is True and the <action> will be taken.  If <var> contains
anything else it will not.

Now the next :

  if NOT <var> then <action>

If <var> is 0 it is True. This will be _logically_ inverted (NOT).  This
makes the
result False.  The <action> will _not_ be taken.

If <var> is not equal to 0 it is False.  Invert it and you get True.  The
<action> will be taken ...

The example 'IF bit_count then si2c_rbyte_lp'  is dirty piece of code.  Why
? because we use a register that should hold only 2-state's (True & False)
as a
counter (256 states for  Byte-counter).  It works fine because if the
counter == 0 it will _logically_ be equal to a True.  If the counter is
anything else than a 0 it will, again logically, be equal to a False.

Greetz,
  Rudy Wieser