It doesn't work because it is not correct!

For a start, 'C' is case-sensitive - so SW1 and Sw1 are not equivalent!

When you use a #define, it works like this:

#define <name> <text>

Then, wherever the preprocessor sees <name>, it simply replaces it with <text>

In your code above,

<name> is SW1

<text> is P_4; - including the semicolon!


Thus, after preprocessing, your code becomes (assuming that you intended SW1 in both cases):

Save This Code

P_4; = 1;      // turn on port
delay(20);     // delay
P_4; = 0;      // turn off port

and the error is immediately obvious!
See: http://www.8052.com/forum/read.phtml?id=29152

I have several references for C, but most use Keil code.

This is basic, plain vanilla, bog-standard 'C' - nothing to do with Keil, SDCC, or any other specific implementation!

As has already been mentioned, you need to learn the basic 'C' language first, before worrying about the extensions offered by Keil, SDCC, etc...