Lpc2000

--- In lpc2000@yahoogroups.com, "wickedmonster2002" <karim@...> wrote:
>
> I am confused. What does #define SPIF (1<<7) mean? Everything else I
> understand.
>

As others have pointed out discovering **what** it means is very 
simple: it's just standard 'C'.

What's less obvious is **why** this construct is used. I believe the 
following is the main reason:

In many peripheral register descriptions, you will see the function of 
individual bits described. This is the case for "SPIF", which is bit 7 
in SPSR. Rather than work out by hand (and perhaps getting it wrong), 
the simplest thing is to get the pre-processor to do it for you. In the 
general case:

#define BIT_NAME (1 << bit_position)

That way it's easy to cross check the definition in the code against 
the documentation.

You can then use it in code to select the bit of interest as follows:

if (S0SPSR & SPIF)
{
  do_something();
}

Brendan