Split from: Storing large, lookup table arrays in FLASH only

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KUNAL GARG
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Posted by KUNAL GARG: Sun. Jul 10, 2016 - 08:57 PM
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I am making lookup table for all alphabets(to be stored in flash memory) and making an array of 26x8 (26 alphabets and 8 hex code per alphabet for 8x8 alphabet on screen) . As we know pixel will get coloured there, where the value of pixel is high (in lookup table) and will remain of back ground color where value is low. So now my doubt is that by pgm_read_byte function, we are able to read lookup table at byte level (like 0xf0) but i want it to read at the bit level (1,1,1,1,0,0,0,0) , only then the pixel will be given the corresponding color value. So how will I do it? one possible method is by creating lookup table for all alphabet in form of 0 and 1 but that will be too lengthy for all characters.My aim is to display any string of user choice on tft screen 7inch (ssd1963 uC with atmega128). Please help for the sake of this discussion platform of avr freaks. thanks in advance as well!

This topic has a solution.

Kunal

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Tools, Compilers and General Programming, solved
Last Edited: Tue. Jul 12, 2016 - 08:20 AM
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Bronze Markjs
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Posted by js: Sun. Jul 10, 2016 - 09:29 PM
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The thread is 12 years old.

John Samperi

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Gold Markclawson
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Posted by clawson: Sun. Jul 10, 2016 - 11:14 PM
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You read a byte and then extract the bit(s) you want. Isn't this obvious? It's the way computers have always worked!

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KUNAL GARG
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Posted by KUNAL GARG: Mon. Jul 11, 2016 - 06:57 AM
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sir, can you please elaborate(may be by giving some example) ?!  thanks!

 

Kunal

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Gold Markclawson
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This reply has been marked as the solution. 
Posted by clawson: Mon. Jul 11, 2016 - 09:36 AM
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KUNAL GARG wrote:

sir, can you please elaborate(may be by giving some example) ?!  thanks!

const __flash pixels[] = {
    0b10010110,
    0b01110110,
    0b11010011
};

bit = pixels[1] & (1 << 3); // get bit3 of 2nd byte

or if you insist on using PROGMEM:

#include <avr/pgmspace.h>

const PROGMEM pixels[] = {
    0b10010110,
    0b01110110,
    0b11010011
};

bit = pgm_read_byte(&pixels[1]) & (1 << 3); // get bit3 of 2nd byte

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Bronze Markbobgardner
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Posted by bobgardner: Mon. Jul 11, 2016 - 05:15 PM
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The Most Patient Man In The World. Bless You.

 

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