TMS320F28377S: Generating a high frequency square wave

Ankit Srivastava

Part Number: TMS320F28377S

Hi,

I am running my system clock at 48 MHz which is fixed for my current design. I would like to generate and output a 10 MHz square wave which will act as a clock for one of the external payloads. I suppose bit-banging a GPIO using a timer interrupt may not be a good idea. Will ePWM be able to generate such high frequency or do I have to use some other method to generate? Just need a heads up towards right direction :)

Thanks and Regards,

Ankit

over 6 years ago

0 Nima Eskandari over 6 years ago

TI__Guru 52040 points

You are running the C2000 device at 48MHz instead of 200MHz?

0 Ankit Srivastava over 6 years ago in reply to Nima Eskandari

Expert 1160 points

Hi Nima,

Yes, due to power constraints of the whole system, I am running it at 48 MHz.

Thanks and Regards,
Ankit

0 Ankit Srivastava over 6 years ago in reply to Ankit Srivastava

Expert 1160 points

Hi Nima,

My question was wrong. It was not square wave of 10 MHz.
I actually want a pulse every second with pulse width 100 nano second. These train of pulses will act as interrupt for an external system.

Thanks and Regards,
Ankit

0 Nima Eskandari over 6 years ago in reply to Ankit Srivastava

TI__Guru 52040 points

Okay then lets do the math, clock is running at 48MHz, the period is around 21ns? then TBPRD of a 5 should do it.

Try it and let me know.

0 Ankit Srivastava over 6 years ago in reply to Nima Eskandari

Expert 1160 points

Hi Nima,

Since I have to output a pulse per second with a pulse width of 100 nanoseconds, I believe it's not possible given the speed I am running my clock.
With the below settings, I managed to get a PWM of 1 Hz with a pulse width of 16 microseconds.

SYSCLK = 48MHz

EPWMCLK = SYSCLK/2 = 48MHz/2 = 24MHz

HSPCLKDIV = 3 (so /6)
CLKDIV = 6 (so /64)

Hence TBCLK becomes 24000000 /(64*6) = 62500 cycles. (Maximum Value which TBPRD can hold is 65535 as it is 16 bit register)
For 1 Hz PWM , TBPRD = 62500..

CTRMODE = COUNT UP

When I put the CMPA as 0 (minimum possible), I get the pulse width as 1/62500= 16 microseconds.
When I put CMPA as 1, I get the pulse width of 32 microseconds.

Thanks and Regards,
Ankit

0 Ankit Srivastava over 6 years ago in reply to Ankit Srivastava

Expert 1160 points

Hi Nima,

Managed to reach pulse width of 8 microseconds in 1 Hz PWM by using up-down mode.
Can I use hardware resolution to generate even smaller pulse width?

Thanks and Regards,
Ankit

0 Nima Eskandari over 6 years ago in reply to Ankit Srivastava

TI__Guru 52040 points

It's not really created to be used for that purpose. The high resolution is for placing the edges in a specific location with around 150ps resolution.

You can try running the EPWM clock at 48MHz. No dividers and get the maximum resolution.

0 Ankit Srivastava over 6 years ago in reply to Nima Eskandari

Expert 1160 points

Hi Nima,

I will keep that in mind. Fow now I will stick to 8 us pulse width at 1 Hz fequency as the best I can achieve. It may be okay for my application.

Thanks and Regards,
Ankit

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TMS320F28377S: Generating a high frequency square wave