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Guest
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newb assistance - arrays |
Posted: Fri May 19, 2006 4:00 am |
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I'm having something of a problem using an array.
Basically I've got a 7*5 LED matrix and am using a 16f628 to drive it.
I've written out a charector map to display some numbers/letter/symbols and put then in a large array.
the trouble is that the array seems to be giving me some problems, I have about 90 numbers/letters/symbols
but I only seem to be able to make an array that has 51 spaces in it.
Code: | const char c32[51][5] = {
{0x00, 0x00, 0x00, 0x00, 0x00},
{0x....
...
...
}; |
works fine,
yet
Code: | const char c32[96][5] = {
{0x00, 0x00, 0x00, 0x00, 0x00},
{0x....
...
...
}; |
gives the error
Quote: | Error[45] Matrix.c 38 : Subscript out of range
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I have version 3.099 (which I know is old).
and am using MPLAB as an IDE
I know that I could split the array in half into 2 arrays and set each a different range of charectors, but that seems a little messy so I though I'd make a post here to see if anyone had any suggestions. |
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Ttelmah Guest
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Posted: Fri May 19, 2006 4:31 am |
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The problem is the total size. Constant array accesses on the 16 chips, are done by adding an offset to the program counter, to 'jump' to a RETLW instruction containing the byte required. The maximum offset possible, is 255. 51*5, just fits into this, but 96*5=480, which can't be handled.
This is a hardware limit of the 16 architecture, not something that is fixed in a latter version. It would be possible for the compiler to do multiple arrays, and 'hide' the problem, but it doesn't.
May I suggest a macro like:
#define c32(x,y) (c32##y[x])
Then if you define five 96 element arrays, c320[n]..c324[n], you can access these as 'c32(n,0)'.
The only 'caveat' with the macro version, is that the second digit has to be a constant text character, rather than a variable. Otherwise just have a function to access the five arrays.
Best Wishes |
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