Generating a PWM with 20% duty cycle on CC 2540

Bita149

Hi Everyone,

I am trying to generate a PWM with a 20% duty cycle using Timer 1. Can anyone help me how I could modify the buzzer.c function to accomplish this task or any-other suggestions?

Thank you in advance,

over 8 years ago

0 YiKai Chen over 8 years ago

Guru 735455 points

Here is the example to output 6.5K PWM to P1.1 with 50% duty cycle

PERCFG |= BV(6); // Select Timer 1 Alternative 2 location
P2DIR = (P2DIR & ~0xC0) | 0x80; // Give priority to Timer 1
P1SEL |= BV(1); // Set P1_1 to peripheral

T1CC0L = 0x3A; // PWM signal period
T1CC0H = 0x01;

T1CC1L = 0x9D; // PWM duty cycle
T1CC1H = 0x00;

T1CCTL1 = 0x1c;

T1CTL |= (BV(2)|0x03); // divide with 128 and to do i up-down mode

You can change T1CC1L and T1CC1H to change duty cycle.

0 Bita149 over 8 years ago in reply to YiKai Chen

Prodigy 245 points

Can you explain how these calculations work? I tried changing the numbers to decimal to try to understand what is happening but I couldnt figure it out. Thank you.

0 Tim C over 8 years ago in reply to Bita149

TI__Mastermind 34660 points

These registers, as well as the timer module in general, are all described in the the TRM (www.ti.com/.../swru191)

0 Bita149 over 8 years ago in reply to Tim C

Prodigy 245 points

Hi tim, I am at this moment looking at the print out of chapters 9 and 10 but I could not find an info on how to make changes to get the desired duty cycle. Am I missing some other chapter or info?

Thanks,

0 Tim C over 8 years ago in reply to Bita149

TI__Mastermind 34660 points

No its all there. The example YiKai posted is using up-down mode and is changing the duty cycle by modifying the compare value.

0 YiKai Chen over 8 years ago in reply to Bita149

Guru 735455 points

You can refer to 9.5 Up-and-Down Mode and Figure 9-6. Output Compare Modes, Timer Up-and-Down Mode in CC253x/CC254x user guide.

0 Bita149 over 8 years ago in reply to YiKai Chen

Prodigy 245 points

Hello,

where do I put this code in the application in order to generate the PWM? I am using the heartrate sensor sample application.

0 Bita149 over 8 years ago in reply to YiKai Chen

Prodigy 245 points

Hello,

where do I put this code in the application in order to generate the PWM? I am using the heartrate sensor sample application. Also what do BV(1) and BV(2) refer to? I could not find those in the sample application.

0 YiKai Chen over 8 years ago in reply to Bita149

Guru 735455 points

You can put those code at where you want to start PWM. As for BV(n), it is defined as "#define BV(n) (1 << (n))".

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Generating a PWM with 20% duty cycle on CC 2540