eeprom locations

[aaronik19]

Dear all, I am trying to assign a particular eeprom location to a variable but for some reason the compiler is giving me an error "Expecting an identifier". What could be wrong? I am using 18F4520 and the code is below:

[Ttelmah]

Several parts:
1) A #define, does not define a variable. It is a _text_ substitution during compilation. So wherever you have the word 'last_scene' for example, the number '1' will be substituted. So if you tried to execute:

last_scene=10;

The resulting 'real' code would be '1=10'. An impossible operation, since a variable identifier is _needed_ on the left of the equation. This is what the compiler is complaining about.
2) The PIC does not have a single linear memory space. It has RAM memory (addressable by variables), and ROM memory in a separate address space. Then the EEPROM exists in a third address space. You can't read/write directly to the address spaces other than the RAM one (there is a sort of way round this, but more complex than it is worth....).
3) Look at the read_eeprom, and write_eeprom functions. These would accept your defined address and a value to read/write. The best way to use the EEPROM.
4) You can access EEPROM as if it is in your memory space, by allocating the read/write functions with ADDRESSMOD. However bulky, and prone to errors.

Big caveat. Be careful how often you change things with any route. If you read/write the EEPROM as if it is a variable, you can kill the chip in a few hours. The EEPROM is designed to be updated _infrequently_.

Best Wishes