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printf??

 
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printf??
PostPosted: Mon Mar 12, 2007 11:17 pm     Reply with quote
Hi
Can anyone explain to me how to use printf instead of using lcd_putc?

And if my input is in analog value, what is the suitable data type should i use? int or int8 or float or int16?

I also dont know the function of %. if i want my output in point, what should i write? Let say i want 7.564

Is it correct printf(%2f output)?
Ttelmah
Guest
PostPosted: Tue Mar 13, 2007 3:57 am     Reply with quote
You use 'lcd_putc', as the 'target' for the printf. So:

printf(lcd_putc,"format string",data to print);

Now really, I'd suggest getting a C primer, since an explanation of what the various formats 'do', would be a multi page document!. However I'll make a suggestion, based upon fairly efficient 'useage' in CCS, and one 'special' CCS format. You will need to put this 'into' a suitable program.
Code:


int16 val; //You want an int16, since the ADC, returns a 10bit value

val=read_adc(); //obviously need to select ADC channel first etc..

//Now assuming you are using the power rail as a reference, and this
//is 5v, you want 5.000 for 1024 counts (will never get this).
//You can do this two ways:

printf(lcd_putc,"%5.3f",(float)val/204.8);

//This converts 'val' into a floating point number (the 'float' bit), and
//scales this to give the right value. Downside, is that it is _bulky_, and
//_slow_. Floating point arithmetic, is not ideal on a small processor...
//The 'layout' is saying 5 characters, with three after the decimal point.

//Now a typical alternative:
val=((val*32)+(val*16))/10;

//This looks a lot more complex, but in computing terms is a lot quicker
//calculation. *32, and *16, are implemented using simple bit shifts.
//The slowest part is the division, and even this only takes about 1/4 the
//clock cycles of the floating point division.

printf(ld_putc,"%5.3lw",val);

//This uses a 'special' format in the CCS compiler, to print an
//integer, as a 'scaled' float. The advantage is that all the arithmetic
//for the printout, is still done using integer maths.

Now the second example,won't be quite accurate, but will be a _lot_ faster. Smile
It'll give a display of 2.457, for 2.5v in. In general, by carefully choosing the voltages involved, it may be possible to do better.

Best Wishes
pijang
Guest
PostPosted: Thu Mar 15, 2007 2:17 am     Reply with quote
Hi.. Razz

Hoho.. Finally my PIC and my LCD display is worked
Thank u for your help.
And also to PCM programmer that help me a lot in understanding
the programming..

Thank u again Laughing
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