Error, Data Item Too Big

[bwhiten]

Ok, I did a search for the above string but found limited info. on the board. The help file lists this error but blank information.
I'm using 4.069, 16F887.
The issue is:
I have and empty segment that states 2048 free. I am trying to #ORG a constant 2-dimensional array of [80][20] chars into this area but I get the "ERROR 87: Data Item Too Big" error.
What are the limitations on 2-dimensional array indecies or am I mistaking free memory for something it's not?

[Matro]

2048 bytes or word-instructions?
If it is 2048 bytes, it is only 1024 different addresses...

Matro

[Ttelmah]

Is this data numbers, or text?.
If the latter, then instead look at the #ROM char option.
On the 16F chips, the program memory, is 14bits wide. Each location, can therefore hold just _one_ byte. However it can hold two 7 bit text characters. This is what the #ROM char option implements. So if it is text, you should use this option to make a massive saving in the storage area involved.
Now, each program memory 'page' on this chip, can hold 1024*14bit words, which requires the hex output file to allocate 2048 'bytes'. However because each real location is only 14bits in size, you can't _store_ 2048 bytes here.
So if you need to store 1600 _characters_, then look at the #ROM option, which will pack these into 800 'words' of storage, and fit them into a page. However if you want to hold 1600*8bit values, then you need to think again, since this won't fit (which is what the compiler is complaining about....).

Best Wishes

[bwhiten]

This is my declaration:

[Ttelmah]

No, characters by default, will be defined as bytes, so each will occupy an entire instruction word in memory. Worse, the const declaration, will include the code to retrieve it as well, making this occupy quite a few more locations....
Yes. write a 'retrieval' routine, using the read_program_memory function. You will need to extract the seven bit values, and handle calculating the right location in this.

Best Wishes

[PCM programmer]

[Ttelmah]

I mention this in my first post.
This is what bwhiten was asking about how you retrieve the data from.
You would need something like (no guarantees...):

[bwhiten]

Thanks for the help. I have several options now to work on. I'm assuming this works for constants and variable data?

[Ttelmah]

No.
Variable data has to be stored in RAM, which is 8bits wide. This _only_ applies to constant data stored in the _program_ memory, which on these chips is large enough to store two seven bit values, but not two 8bit values (on the 18 chips, the program memory is wider).

Best Wishes

[bwhiten]

OK I guess I'm still a little confused. Are the:
"write_program_memory" and "read_program_memory" functions not useable in real-time?

Or am I confusing me/you with "variable" instead of "variable data at a memory location"?
I take it as long as I keep track of where a certain piece of data is I can use the _program_memory functions all day long.

[Ttelmah]

You can use read_program_eeprom, as much as you want. However the _write_ functions, must be treated with a lot of care. The chip has a limited life for write cycles to this memory. Typically anything from 10000, to 100000 cycles depending on the chip. Also the memory is organised into pages, and a whole page must be erased, and re-written to write just a single byte. The writes are also _slow_ typically in the order of perhaps 4mSec (an age in computer terms).
If you realise that (for example), changing a value once a second, could use up the write life on even the 'better' chips in this regard, in a little over a day, you will begind to understand why writing these values, should only be done as little as possible....
The EEPROM, is specifically designed to store values you want to keep, and should be used in preference (has usually many times the life - typically perhaps 100*).

Best Wishes

[bwhiten]

Now I understand better. Useable but not meant for repeated writes. Constants or data storage for boot time options I guess would be OK.
The memory areas of these chips have quite a few similar names when you look through the device file, datasheet, etc. The device file alone lists, Program memory, RAM, Data EEPROM.