AVR-Chat

This is easy to do and produces optimal code on GCC (e.g. sbi/cbi when
appropriate):

typedef union	// Delclare a union that allows bit & byte access
{
	unsigned char byte;		// This is a byte for 8 bit access
	struct
	{
		unsigned char P0:1;	// These are bit-fields
		unsigned char P1:1;
		unsigned char P2:1;
		unsigned char P3:1;
		unsigned char P4:1;
		unsigned char P5:1;
		unsigned char P6:1;
		unsigned char P7:1;	// We can use an anonomous struct
	};					// because the bit names are unique.
} sfr_struct;

#define PORTB (*(sfr_struct *)0x38)	// Cast the sram address to the
structure

...

#define MOTOR_ENABLE_PIN PORTB.P2	// Now make an alias for your bit

...

MOTOR_ENABLE_PIN = TRUE;		// Now, just use it.

If you want to access the port as a byte value, then use:

PORTB.byte = ...

-----Original Message-----
From: Stefan Trethan [mailto:stefan_trethan@gmx.at]
Sent: Monday, January 31, 2005 7:14 AM
To: AVR-Chat@yahoogroups.com
Subject: Re: [AVR-Chat] accessing bits (e.g. of ports)



On Mon, 31 Jan 2005 09:47:49 -0500 (EST), <ethan@bufbotics.org> wrote:

>
> <code>
> if (turn_motor_on) {
>    setbit(MOTOR_ENABLE_PORT, MOTOR_ENABLE_PIN);
> } else {
>    clrbit(MOTOR_ENABLE_PORT, MOTOR_ENABLE_PIN);
> }
> </code>
> Personally, I would prefer something like.....
> <code>
> write_bit(turn_motor_on, MOTOR_ENABLE_PORT, MOTOR_ENABLE_PIN);
> </code>

You could make that with a define i think. I guess even i could figure out
how eventually.

But well, wouldn't it be great if one could just write

MOTOR_ENABLE_PIN = turn motor on;

or, if need be

MOTOR_ENABLE_PORT.MOTOR_ENABLE_BIT = turn motor on;


I have the same situation here.
I don't understand why that doesn't work. I'm no programmer as everyone
sees easily, but when reading various stuff i get the impression "well, if
you don't use bit operations you aren't a proper programmer, get lost.".
That might well be true, and i'm not a proper programmer, but i still
don't understand why i must fight with &|!<< to change or read a single
bit.
I mean, life is hard enough, why make it any harder?


Why exactly is't a bit just a variable like for example PORTB?
I can write PORTB=0xFF; but can't do the same with bits.

ST



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