Newbie needs help to make a lookup table

[John_Lintern]

I need to use a lookup table of some sort but I have no idea how to do it !

I need a value to be looked up from two variables, 'Throttle Position' and 'RPM'.

Both these variables are 8-bit integers ranging from 0 to 255.

The lookup value will also be an 8-bit integer ranging from 0 to 255.

So I need to create a MAP, just like the fuel and ignition MAPS used in engine management control units.

If I used a lookup table for every value of the two inputs I would have a table of 65,025 bytes ! (255*255)

So I have reduced this by using a resolution of 5 for the 'Throttle Position' and a resolution of 4 for the 'RPM', this gives me a table of 3,328 bytes (52*64).

i.e.

0 4 8 12 16 20 24 28 32 ......252
5
10
15
20
25
...
...
...
255

The values of the lookup table will probably be stored in an external eeprom at a later date.

But for now, what is the best way for me to create a lookup table ?

Can I use something like...

BYTE CONST SINE_WAVE[200,100] = {
128,132,136,139,143,147,150,154,158,161,165,169,172,176,179,
182,186,189,192,195,199,202,204,207,210,213,215,218,220,223,
225,227,229,231,233,235,237,238,240,241,242,243,244,245,246,
247,247,247,248,248,248,248,248,247,247,247,246,245,244,243,
242,241,240,238,237,235,233,231,229,227,225,223,220,218,215,
213,210,207,204,202,199,195,192,189,186,182,179,176,172,169,
165,161,158,154,150,147,143,139,136,132,128,124,120,117,113,
109,106,102,98,95,91,87,84,80,77,74,70,67,64,61,57,54,52,49,
46,43,41,38,36,33,31,29,27,25,23,21,19,18,16,15,14,13,12,11,
10,9,9,9,8,8,8,8,8,9,9,9,10,11,12,13,14,15,16,18,19,21,23,
25,27,29,31,33,36,38,41,43,46,49,52,54,57,61,64,67,70,74,77,
80,84,87,91,95,98,102,106,109,113,117,120,124};


I tried to compile my program with this code inserted but it came up with an error.

It highlighted the 200 (in the line BYTE CONST SINE_WAVE[200,100]) and said 'Expecting a ]'.

Can anyone offer some help ?

PS. I am using a PIC16C74B

[Mark]

It should look something like this

[SherpaDoug]

At least to start you might try 52 lookup tables of 64 entries each. Use a switch case to select which table to use. It will a lot easier for the compiler to deal with.
_________________
The search for better is endless. Instead simply find very good and get the job done.

[John P]

I've had trouble with very large lookup tables, though I have an ancient compiler version and maybe there's a way to do it now.

What I do is write a program on the PC to generate the table in Intel hex form, then splice it into the hex file that the compiler produces, load it to the processor as usual and use read_program_eeprom() to get the data out of ROM. As a bonus, you get 14 bits for each location.