#define and #byte

[mle]

Hello,
Can someone please clarify the difference between a #define and #byte.
When I define the different registers, I thought I would use

#define PORTA 0x05

but then I get an error when I do

PORTA =0;

When I am defining EEPROM variables should I use #define or #byte?

Thanks,
mle

[truevenik]

hi,

#define PORTA 0x05
PORTA = 0
is equivalent to just writing
0x05 = 0 (try to assign 0 to a litteral value = error -this is like writing 3=1)

#byte PORTA = 0x05
PORTA = 0
I think is equivalent to writing
*0x05 = 0 (store 0 in an address = no error)

In general, when you do #define <a> <b>, the compiler blindly goes through and replaces all occurences of <a> with <b> - its almost like find-replace in a text editor. #byte is different: Normally, when you define a variable (eg. int x), the compiler decides which memory address to use. #byte allows you to explicitly tell the compiler to use a specific RAM address for the variable - it associates a RAM address with a name.

I don't know what you mean by defining eeprom variables. the above code just names a register in the register file (RAM).
To store to EEPROM if I remember correctly, you have to put an address in a register, and data in another register. both of these registers can be written in exactly the same way you would write something to portA.

[rnielsen]

You might want to consider keeping your code as portable as possible. To do this you would use output_a(0) which will write all zero's to the port.

Happy frustrations.

Ronald