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read_program_eeprom problem with big table!!

 
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cagacug



Joined: 14 Apr 2004
Posts: 5

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read_program_eeprom problem with big table!!
PostPosted: Wed Apr 14, 2004 4:18 pm     Reply with quote
Hi to All,

Classical read rom problem!!

Using PIC 16f877, compiler v 3.184.

I have a big lookup table in the rom which I insert it with #ORG and #ROM instructions. The table contains appr. 1300 bytes starting from adress 0x1800.

I read the data with "read_program_eeprom", I use the exact code like this :

temp1 = read_program_eeprom (0x1800 + (cur_chr*5) + cur_col - 1);

which works fine for the first 256 items, but gives unexpected values for the rest. When I change the starting adress of the ROM to something like :

temp1 = read_program_eeprom (0x1900 + (cur_chr*5) + cur_col - 1);

again works for another 256 items but gives unexpected results for the rest. I also tried putting all the adress data to a long variable and then calling the function like:

long adres;
adres = 0x1900 + (cur_chr*5) + cur_col - 1;
temp1 = read_program_eeprom (adres);

, it didnt work.

Anyone have an idea?

Thanks
Ttelmah
Guest
Re: read_program_eeprom problem with big table!!
PostPosted: Wed Apr 14, 2004 4:28 pm     Reply with quote
cagacug wrote:
Hi to All,

Classical read rom problem!!

Using PIC 16f877, compiler v 3.184.

I have a big lookup table in the rom which I insert it with #ORG and #ROM instructions. The table contains appr. 1300 bytes starting from adress 0x1800.

I read the data with "read_program_eeprom", I use the exact code like this :

temp1 = read_program_eeprom (0x1800 + (cur_chr*5) + cur_col - 1);

which works fine for the first 256 items, but gives unexpected values for the rest. When I change the starting adress of the ROM to something like :

temp1 = read_program_eeprom (0x1900 + (cur_chr*5) + cur_col - 1);

again works for another 256 items but gives unexpected results for the rest. I also tried putting all the adress data to a long variable and then calling the function like:

long adres;
adres = 0x1900 + (cur_chr*5) + cur_col - 1;
temp1 = read_program_eeprom (adres);

, it didnt work.

Anyone have an idea?

Thanks

If 'cur_chr' or 'chr_col', are integers, remember the actual arithmetic used for the calculations will only be 8bit. Try with:
adres = 0x1900L + ((int16)cur_chr*5) + ((int16)cur_col - 1);
CCS C, does not 'promote forward' types. On most C compilers, if one part of the arithmetic is a 'long', all the arithmetic will be long. On the CCS C, instead only the parts containing a long will be performed using long arithmetic. This saves space, but means you must be aware to 'cast' up when needed.

Best Wishes
cagacug



Joined: 14 Apr 2004
Posts: 5

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read_program_eeprom problem
PostPosted: Thu Apr 15, 2004 12:10 am     Reply with quote
Thank you very much , that is the exact problem, and solved.
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