TMS320F28335: Issue with Frequency Output in custom PCB Based on TMS320F28335PTPS Using TI XDS 110 Debug Probe.

Hello,

Can you share a screenshot of the clock irregularities and the code you are using to initialize the PLL?

Best,

Matt

’m trying to generate a 5 kHz signal using GPIO and EPWM , and while the Scope shows the correct 5 kHz frequency, the hardware output shows around one-third of that frequency. There’s no PLL involved in the setup. i have attached scope output and code images.

Hi Atul,

Atul saurabh said:

and while the Scope shows the correct 5 kHz frequency, the hardware output shows around one-third of that frequency

Can you please help clarify what you are scoping and what you mean by 'hardware output'? Are these two different sources? 

Atul saurabh said:

This irregularity leads me to suspect there might be an issue related to the clock configuration or the crystal itself

What is your clock configuration setup?

Atul saurabh said:

m trying to generate a 5 kHz signal using GPIO and EPWM

Do both of these methods give you one-third of that frequency?

Best Regards,

Marlyn

I’m generating a 5 kHz signal, and it shows the correct frequency on the Scope. However, when I dump the code into the MCU (F28335), the frequency becomes one-third of the expected value. hardware output means output from MCU after dumping code and from same sources. and both of these methods gives me one third of that frequency.

Hi,

What are your SysCtrl settings i.e. how do you initialize the peripheral clocks? The frequency being 1/3 the expected value makes me suspect that the code is assuming a 10 MHz clock, not 30 MHz.

Best,

Matt

Hi,

The system control clocking is quite different between F2837xD and F2833x devices, although it's interesting to know that it worked on the F2837xD LaunchPad.

Can you please still share what your SysCtrl settings are for the F2833x code, specifically what you're configuring in the PLLCR and PLLSTS registers?

Best,

Matt