PIC Memory varaibles declaration

haxan

New Member

• Dec 8, 2009

• #1

Hi. I just want to know one simple thing.

How to define variable in Program Memory and Data memory separately using C language and C18 compiler.

Also does putting static give any memory saving advantage or is it just a programming practice to avoid overwriting ?

 

P

Pommie

Well-Known Member

Most Helpful Member

• Dec 8, 2009

• #2

You define the two with ROM and RAM directives.

Static generates a global variable whose scope is limited to where it is defined and so it uses more memory than a non static variable as that memory can't be reused.

Mike.

 

haxan

New Member

• Dec 8, 2009

• #3

Thank you Pommie.

The problem with ROM is that it cannot be overwritten (but i guess thats what ROM means).

Also when we declare variable like unsigned char , It is defined in RAM ?

 

Last edited: Dec 8, 2009

P

Pommie

Well-Known Member

Most Helpful Member

• Dec 8, 2009

• #4

Normally yes, ROM = read only. However, on pics it can be written to and C18 does most of the code for you. It sets up all the registers but doesn't do the actual write.

Mike.

 

haxan

New Member

• Dec 8, 2009

• #5

if the variable are by default defined in RAM, whats the use of writing RAM before variables then?

 

P

Pommie

Well-Known Member

Most Helpful Member

• Dec 8, 2009

• #6

Just for clarity, so someone working on your code in 10 years time has a better idea of what the variable is.

Mike.