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 10 years ago

0 YiKai Chen over 10 years ago

Guru 735685 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 10 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 10 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 10 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 10 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 10 years ago in reply to Bita149

Guru 735685 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 10 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 10 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 10 years ago in reply to Bita149

Guru 735685 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