TMS320F28335: Default PWM state

Rohit Baranwal

Part Number: TMS320F28335

Hi,

I need to know the default state of the ePWM outputs (all six modules) when the processor starts. In section 6.2 of the 'Systems Controls and Interrupts' guide, it is said that the internal pullups are disabled by default for the ePWM pins. Does it mean that these outputs are LOW by default or are they tri state in the default condition?

I have a custom F28335 board and the ePWM outputs are all high when the processor boots up and I have not loaded any program in the RAM. This is not consistent with the description given in the guide.

over 8 years ago

0 Brett Larimore over 8 years ago

TI__Guru 57255 points

Hi Rohit,

Please see the following wiki:
http://processors.wiki.ti.com/index.php/General_Purpose_IO_%28GPIO%29_FAQ_for_C2000#Q:_Are_the_pull-ups_on_pins_that_can_be_used_as_ePWM_outputs_enabled_or_disabled_on_reset.3F

You'll want to look at the reset state of each of the GPxPUD register bits.

You can do the same for GPxMUXn and GPxDIR. (however, all the GPIO pins are set up as GPIO & GPIO inputs at reset)

Hopefully this helps!

Thank you,
Brett

0 Rohit Baranwal over 8 years ago in reply to Brett Larimore

Expert 1025 points

Hi Brett, the information on the link matches that given in the manual. However, what does having a disabled pullup mean? Does it mean that the output is LOW by default, or is tri state by default?

0 Brett Larimore over 8 years ago in reply to Rohit Baranwal

TI__Guru 57255 points

Hi Rohit,

I'm going to split your question into two parts.

1) All GPIO pins are configured as GPIO inputs at start-up (as defined by GPxMUXn and GPxDIR). This means the GPIO pin will not be driven.
2) Based on the status of GPxPUD on reset, some GPIO will have internal pull-up circuitry active on start up.

On GPIOs where the pull-up is enabled on reset: the GPIO will be undriven, but will be pulled to 3.3V by the pull-up circuitry. Note that this internal pull-up circuitry could be overdriven by a stronger external pull-down, if desired.

On GPIOs where the pull-up is disabled on reset: the GPIO will be floating.

Thank you,
Brett

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TMS320F28335: Default PWM state