Hello guys,

I've a program which contains this code

#define rs PB0
#define rw PB1
#define en PB2

and later it is used as

void lcd_cmd(int x)
{
PORTB=x;
PORTB &= ~(1<<rs);
PORTB &= ~(1<<rw);
PORTB |= (1<<en);
_delay_ms(2);
PORTB &= ~(1<<en);
}

My question is why we used PB0, PB1 and PB2 instead of 0, 1 and 2 ??

doesn't the below code make more sense?

void lcd_cmd(int x)
{
PORTB=x;
PORTB &= ~(1<<0);
PORTB &= ~(1<<1);
PORTB |= (1<<2);
_delay_ms(2);
PORTB &= ~(1<<2);
}

Please help, it's very urgent.

Thanks.

 

Why would someone write

PORTB |= (1<<2);

when it is easier to write

PORTB |= 0x04;

The reason one would choose to write PB0, PB1, and PB2 is that one could easily change the port assignments to different pins, for example PB5, PB6, PB7.

 

Why would someone write

PORTB |= (1<<2);

when it is easier to write

PORTB |= 0x04;

The reason one would choose to write PB0, PB1, and PB2 is that one could easily change the port assignments to different pins, for example PB5, PB6, PB7.

sorry I didn't mean that. What I wanted to say is why not use this code

#define rs 0 
#define rw 1
 #define en 2

which will produce

void lcd_cmd(int x)
{
PORTB=x;
PORTB &= ~(1<<0);
PORTB &= ~(1<<1);
PORTB |= (1<<2);
_delay_ms(2);
PORTB &= ~(1<<2);
}

why we are writing PB0 instead of 0 in #define

 

Statements such as

#define rs PB0

belong in a .h header file, not in the main code or module.

This allows one to reuse the same code even though the hardware assignment has changed.

This is simply sound systems design practice.

Better still, one could use

#define LCD_PORT PORTB
#define rs 0
#define rw 1
#define en 2

This would allow you to choose any port and pin.

 

why we are writing PB0 instead of 0 in #define

Because people are not computers.

People will at least have a feeling as to what PB0 means, as opposed to "0".

What does "0" mean? That is extremely dependent on the contest.

PB0, given the general context of doing a program, has but one meaning: the lowest pin of a port.

A very wise man once said "Never put a magic number into your code."

"0" is a magic number. "PB0" is well on it's way to being a self-documenting symbol.

 

Better still, one could use

#define LCD_PORT PORTB
#define rs 0
#define rw 1
#define en 2

This would allow you to choose any port and pin.

That is NOT better. You are using magic numbers.

While you state WHERE they are used you do not state WHY they are used.

#define rs PB0
#define rw PB1
#define en PB2

Shows everyone the port pin rs uses, while the former is quite obscure.

 

This will work because PB0, PB1 and PB2 are defined as 0, 1, 2.

Ernie is correct because if you wanted to change to PORTE, for example:

#define LCD_PORT PORTE
#define rs PE5
#define rw PE7
#define en PE2

would also work.

Edit: Of course you do have a problem if rs is PB0 and rw is PE7, for example.