CCS/TMS320F28027F: SINE WAVE look up table

Rahul Goel1

Other Parts Discussed in Thread: TMS320F28335

Tool/software: Code Composer Studio

HELLO EVERYONE,

I WAS WORKING ON F28027 FOR THE GENERATION OF A SINE WAVE USING PWM ,I HAVE SUCCESSFULLY CONFIGURED THE PWM BUT NOW I WANT TO GENERATE A SINE WAVE OF 50 HZ ,SO CAN ANYONE PLEASE HELP TO DO SO AND LOOK CAN ANYBODY PLEASE TELL HOW TO INCULDE THE SINE TABLE IN THE CODE AS I DIDN'T FIND ANY DOCUMENTATION FOR THAT,THIS WILL BE REALLY REALLY A GREAT HELP .

THANKS

RAHUL GOEL

over 6 years ago

0 Cody Watkins over 6 years ago

TI__Mastermind 42195 points

Rahul,

I can think of 3 steps to getting a Look Up Table (LUT) into memory.

Define the LUT as an array using a Pragma

You need to determine the number of elements in your LUT by taking your desired sine wave frequency and dividing that by your control loop frequency.

#pragma DATA_SECTION(QuadratureTable,"QuadratureTableSection")

// quadrature look-up table: contains 5 quadrants of sinusoid data points
int QuadratureTable[QUAD_TABLE_LENGTH] = {
		0x0000,			// [0]  0
		0x18F8,	        // [1]  11.25
		.
		.
		.
		0x7D89 	        // [n] 78.75
		};

Place that Pragma into memory using your .cmd file

SECTIONS            /* program sections allocation */
{
                QuadratureTableSection              : > DRAML1,                       PAGE = 1                              /* sine wave look-up table */
...

Extern and use the array in your main.c
1. ```
extern int QuadratureTable[x]; 
```

Finally use the array to adjust the CMPx values of the PWM.

Please note that the above is only an approximation of the code you will need, I do not expect it to build. You should be able to look up the exact syntax.

Regards,
Cody

0 Rahul Goel1 over 6 years ago in reply to Cody Watkins

Intellectual 540 points

THANKS CODY, FOR THE REPLY,

Can you please help to find the value in giving the formula to find the look up table values and also SHOULD WE ADD A FLOATING POINT NUMBER OR ANY OTHER CONVERTED FORM OF NUMBER IN LUT(LOOK UP TABLE).

REGARDS

RAHUL GOEL

0 Richard Poley over 6 years ago in reply to Rahul Goel1

TI__Mastermind 27200 points

Rahul,

You will have to work out the syntax to generate the sine table entries. It is straightforward using Excel, for example, but there are no examples I can point you towards from TI so you will have to work through the details yourself.

If I were doing it, I would use the decimal to hex conversion in Excel to generate entries between 0 and 0xFFFF. That way you can scale each value according to the PWM period in your code and write it to the PWM compare register. This device is fixed-point, so will not be efficient when handling floating point data - I recommend you only have fixed point values in the table.

Regards,

Richard

0 muhammad usama over 5 years ago

Intellectual 340 points

Hello Rahul,

Hope you are doing well

I have just started with TMS320F28335, so I have some basic questions if you can answer it will helpful for me.

1) how to set up the system clock as I am using external clock)

2)how to set up the system memory

3)how to confirm the computation

4)how to generate a simple PWM

Looking forward to you

0 Richard Poley over 5 years ago in reply to muhammad usama

TI__Mastermind 27200 points

Muhammad,

Your questions seem unrelated to those earlier in this thread so I'm going to close this one.

You may find useful information in the hands-on workshop for the device you mention, here:

https://training.ti.com/c2000-f2833x-microcontroller-workshop

If you still need more support, please open a new question on the forum so the right experts can be assigned to it. Thanks.

Regards,

Richard

C2000™︎ microcontrollers

C2000 microcontrollers forum

CCS/TMS320F28027F: SINE WAVE look up table