Lpc2000

I am confused. What does #define SPIF (1<<7) mean? Everything else I
understand.

wickedmonster2002 wrote:

> I am confused. What does #define SPIF (1<<7) mean? Everything else I
> understand.
>
1<<7 means 1 binary shifted left 7 places (bits). The result is 0x80 or 
8'th bit set to 1. It is equal to:

#define SPIF 0x80

It creates a pre-processor definition (#define) such that where ever SPIF is
used in the code it compiles it as though it was: (1<<7).
Or if you mean what does 1<<7 do? Then the << is a bitwise operator in C
that shifts the value (in this case 0x01) 7 places to the left becomes 0x80.

Get yourself a decent book on C, there's plenty out there...

Andy

-----Original Message-----
From: lpc2000@yahoogroups.com [mailto:lpc2000@yahoogroups.com]On Behalf
Of wickedmonster2002
Sent: 11 May 2006 15:42
To: lpc2000@yahoogroups.com
Subject: [lpc2000] LPC2200 Application Note on SPI (AN10369)


I am confused. What does #define SPIF (1<<7) mean? Everything else I
understand.







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wickedmonster2002 wrote:

>I am confused. What does #define SPIF (1<<7) mean? Everything else I
>  
>
What is 2 raised to the 7th power?  This is a C statement to shift a 
value of "1" left by "7" bit positions.

Simply write a binary "1" followed by 7 "0"s.  Then convert the binary 
number into your favorite number base: octal, hex or decimal.

Next, use your calculator to raise 2 to the 7th  power.  See the 
relationships?

TomW

-- 
Tom Walsh - WN3L - Embedded Systems Consultant
http://openhardware.net, http://cyberiansoftware.com
"Windows? No thanks, I have work to do..."
----------------------------------------------------

--- 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

Thanks guys for all the variable answers. I am pro in Assembly
programming. I m just getting into C. I was used to C++ before, but
that was before I got into Embedded systems.


--- In lpc2000@yahoogroups.com, "wickedmonster2002" <karim@...> wrote:

>
> I am confused. What does #define SPIF (1<<7) mean? Everything else I
> understand.
>

Hey Karim are u into weighing scales by any chance.

wickedmonster2002 <karim@...> wrote:  Thanks guys for all the variable answers. I am pro in Assembly
programming. I m just getting into C. I was used to C++ before, but
that was before I got into Embedded systems.


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






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Yes I am...I just got into it a month and half ago. Excellent Educated
Guess by the way.


--- In lpc2000@yahoogroups.com, jk jlkj <njad2002@...> wrote:
>
> Hey Karim are u into weighing scales by any chance.
> 
> wickedmonster2002 <karim@...> wrote:  Thanks guys for all the
variable answers. I am pro in Assembly
> programming. I m just getting into C. I was used to C++ before, but
> that was before I got into Embedded systems.
> 
> 
> --- In lpc2000@yahoogroups.com, "wickedmonster2002" <karim@> wrote:
> >
> > I am confused. What does #define SPIF (1<<7) mean? Everything else I
> > understand.
> >
> 
> 
> 
> 
> 
> 
>   SPONSORED LINKS 
>         Microcontrollers   Microprocessor   Intel microprocessors 
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>     
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>     To unsubscribe from this group, send an email to:
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where r u working from, ru in the US.

wickedmonster2002 <karim@...> wrote:  Yes I am...I just got into it a month and half ago. Excellent Educated
Guess by the way.


--- In lpc2000@yahoogroups.com, jk jlkj <njad2002@...> wrote:
>
> Hey Karim are u into weighing scales by any chance.
> 
> wickedmonster2002 <karim@...> wrote:  Thanks guys for all the
variable answers. I am pro in Assembly
> programming. I m just getting into C. I was used to C++ before, but
> that was before I got into Embedded systems.
> 
> 
> --- In lpc2000@yahoogroups.com, "wickedmonster2002" <karim@> wrote:
> >
> > I am confused. What does #define SPIF (1<<7) mean? Everything else I
> > understand.
> >
> 
> 
> 
> 
> 
> 
>   SPONSORED LINKS 
>         Microcontrollers   Microprocessor   Intel microprocessors 
>     
> ---------------------------------
>   YAHOO! GROUPS LINKS 
> 
>     
>     Visit your group "lpc2000" on the web.
>     
>     To unsubscribe from this group, send an email to:
>  lpc2000-unsubscribe@yahoogroups.com
>     
>     Your use of Yahoo! Groups is subject to the Yahoo! Terms of
Service. 
> 
>     
> ---------------------------------
>   
> 
> 
> 
>                         
> ---------------------------------
> Yahoo! India Answers: Share what you know. Learn something new.
Click here
> Send instant messages to your online friends - NOW
> 
> [Non-text portions of this message have been removed]
>







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---------------------------------
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