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Hi,
I would like to program a DDS (AD9951).
The frequency tuning word (FTW) must be calculated to have a good frequency output (Fo).
Using also the frequency of DDS clock (Fs)
My DDS clock is 360MHz = 360^6
Fo = (FTW)(Fs)/2^32 (given by Analog device)
- As I want to send FTW to the DDS for 10MHz (Fo)
FTW = (2^32x10^6)/360^6 (this is true ?)
but I don't know how to calc these big numbers... (with long ?)
thanks for helping
Oh... it seems that formula is not good...
The good formula:
FTW = 2E32 x (Fo/Fs)
Same pb with 2E32...
Any idea ?
PicBasic code will work with that part?
Not sure if this will help but please consider;
Fr (frequency resolution) = 360000000/2^32 = 0.08381903171539306640625 Hz
FTW = INT(Fo / Fr)
FTW = INT(10000000 / 0.08381903171539306640625) = 119304647
or using reciprocal multiplication (with a constant 1 / Fr = 11.9304647);
FTW = INT(Fo * (1 / Fr))
FTW = INT(10000000 * (11.930464711111111111111111111111)) = 119304647
Good luck on your project...
Cheerful regards, Mike, K8LH
PBP doesn't have decimals, and (2^32 * 10e6) takes more than 32-bit LONGs.
But using some 64-bit math works out pretty good.
With the N-Bit_Math module from ... http://www.picbasic.co.uk/forum/showthread.php?t=12433
Which shows a result of ...Code:<font color="#000000"><b>PRECISION </b><font color="#008000"><b>CON </b></font><font color="#800000"><b>8 </b></font><b>SYSTEM </b><font color="#0000FF"><b><i>' 8 bytes = 64-bit
</i></b></font><font color="#008000"><b>INCLUDE </b></font><font color="#FF0000">"N-Bit_Math.pbp"
</font><b>Base </b><font color="#008000"><b>VAR BYTE</b></font>[<b>PRECISION</b>]
<b>Fo </b><font color="#008000"><b>VAR BYTE</b></font>[<b>PRECISION</b>]
<b>Fs </b><font color="#008000"><b>VAR BYTE</b></font>[<b>PRECISION</b>]
<b>FTW </b><font color="#008000"><b>VAR BYTE</b></font>[<b>PRECISION</b>]
<font color="#008000"><b>ASM
</b></font><font color="#000080">MOVE?CP 4294967295, _Base </font><font color="#0000FF"><b><i>; 2^32 - 1
</i></b></font><font color="#000080">MOVE?CP 10000000, _Fo </font><font color="#0000FF"><b><i>; desired frequency out
</i></b></font><font color="#000080">MOVE?CP 360000000, _Fs </font><font color="#0000FF"><b><i>; DDS clock
</i></b></font><font color="#000080">MATH_MUL _Base, _Fo, _FTW </font><font color="#0000FF"><b><i>; 2^32 * Fo
</i></b></font><font color="#000080">MATH_DIV _FTW, _Fs, _FTW </font><font color="#0000FF"><b><i>; / Fs
</i></b></font><font color="#008000"><b>ENDASM
HSEROUT </b></font>[<font color="#FF0000">" FTW="</font>,<font color="#008000"><b>HEX2 </b></font><b>FTW</b>(<font color="#800000"><b>3</b></font>),<font color="#008000"><b>HEX2 </b></font><b>FTW</b>(<font color="#800000"><b>2</b></font>),<font color="#008000"><b>HEX2 </b></font><b>FTW</b>(<font color="#800000"><b>1</b></font>),<font color="#008000"><b>HEX2 </b></font><b>FTW</b>(<font color="#800000"><b>0</b></font>),<font color="#800000"><b>13</b></font>,<font color="#800000"><b>10</b></font>]
<font color="#008000"><b>STOP
</b></font>
FTW=071C71C7
Which is the hex value for 119,304,647
The value is located in the lower 4 bytes of the FTW array and can be easily shifted out to the DDS.
HTH,
WOW ! It works !
Thank You Darrel
But... I have tried to use a variable for Frequency output and it doesn't work anymore...
Code:PRECISION CON 8 SYSTEM ' 8 bytes = 64-bit
INCLUDE "N-Bit_Math.pbp"
define osc 4
FOUT var LONG
Base VAR BYTE[PRECISION]
Fo VAR BYTE[PRECISION]
Fs VAR BYTE[PRECISION]
FTW VAR BYTE[PRECISION]
high portc.6
FOUT = 1000000
ASM
MOVE?CP 4294967295, _Base ; 2^32 - 1
MOVE?CP _FOUT, _Fo ; desired frequency out
MOVE?CP 360000000, _Fs ; DDS clock
MATH_MUL _Base, _Fo, _FTW ; 2^32 * Fo
MATH_DIV _FTW, _Fs, _FTW ; / Fs
ENDASM
serout2 portc.6,84,[" FTW=",HEX2 FTW(3),HEX2 FTW(2),HEX2 FTW(1),HEX2 FTW(0),13,10]
STOP
MOVE?CP is for constants.
Use MOVE?LP for LONG variables.
Darrel... you're wonderful !
http://www.procrastin.fr/blog/images...iere%20(s).jpg
ADDED:
Since you are using PBPL, you can also move the result back to a LONG...Code:PRECISION CON 8 SYSTEM ' 8 bytes = 64-bit
INCLUDE "N-Bit_Math.pbp"
FOUT var LONG
Base VAR BYTE[PRECISION]
Fo VAR BYTE[PRECISION]
Fs VAR BYTE[PRECISION]
FTW VAR BYTE[PRECISION]
FTWL VAR LONG
high portc.6
FOUT = 10000000
ASM
MOVE?CP 4294967295, _Base ; 2^32 - 1
MOVE?LP _FOUT, _Fo ; desired frequency out
MOVE?CP 360000000, _Fs ; DDS clock
MATH_MUL _Base, _Fo, _FTW ; 2^32 * Fo
MATH_DIV _FTW, _Fs, _FTW ; / Fs
MOVE?PL _FTW, _FTWL ; move result to a LONG var
ENDASM
serout2 portc.6,84,[" FTW=",HEX8 FTWL," = ",DEC FTWL,13,10]
STOP