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TMS320F28377D-EP: External oscillator connection

Danilo A.
Mastermind 34720 points

Part Number: TMS320F28377D-EP
Other Parts Discussed in Thread: UNIFLASH

Hi Team,

Posting on behalf of our customer.

I will share this post with our customer so he can reply when needed.

 

I have a question regarding the 28377FD external oscillator.

I am using a 20MHz external oscillator.

The oscillator's GND is connected to the 28377D's VSSOSC (122),

but the oscillator's power supply VDDOSC is not connected to the 28377D. (Due to a circuit diagram error)

However, the firmware download and functions are working.

Is the external oscillator clock being used even without connecting VDDOSC?

Or, I am curious if it is operating using the internal oscillator.

Not connected due to circuit diagram error.

Regards,

Danilo

  • 0
    TI__Mastermind 45120 points

    Hello Danilo,

    Firmware downloading may work since device might be using the internal oscillator for system clocking.  In order for the device to generate the system clock from an external source (in this case with XTAL), VDDOSC pins have to be connected to 3.3V rail.  VDDOSC is the supply for the external oscillator circuit  and it has to be powered on externally in order for the crystal oscillator to function.

    Best regards,

    Joseph

  • 0 in reply to Joseph Casuga
    TI__Mastermind 34720 points

    Hi Joseph,

    Thank you for your response. Please see our customer's follow up inquiries.

    I am writing to you with additional inquiries.

    The circuit uses an external oscillator, and the external oscillator's power supply is not connected to the DSP's VDDOSC.

    The external oscillator's clock is input to the DSP's X1, while X2 is set to NC.

    The DSP's VSSOSC is connected to the external oscillator's GND.

    Question 1. General functions, such as program downloads and executions, were possible. I would like to know if this operation was powered by the external oscillator or by the DSP's internal oscillator (or crystal).

    Question 2. If the oscillator output clock is applied to X1 while the DSP is unconnected to VDDOSC, I would like to know if the DSP recognizes that clock.

    Regards,

    Danilo

  • 0 in reply to Danilo A.
    TI__Mastermind 45120 points

    Hello Danilo,

    Danilo A. said:
    Question 1. General functions, such as program downloads and executions, were possible. I would like to know if this operation was powered by the external oscillator or by the DSP's internal oscillator (or crystal).

    JC: Program downloads through CCS or uniflash will use the 10MHz internal oscillator, not the external clock.  Execution of code will work but code would have detected a missing clock due to external oscillator not powered up and would automatically switch to internal oscillator.  Execution will run at much lower speed in this case.

    Danilo A. said:
    Question 2. If the oscillator output clock is applied to X1 while the DSP is unconnected to VDDOSC, I would like to know if the DSP recognizes that clock.

    JC: No, external clock will not be recognized.  Device will detect a missing clock and would automatically switch to internal oscillator to get the device running and not stuck due to missing clock.  MCD (missing clock detect) can be processed as an ISR so that it can be handled effectively when no clock is detected.  Through the ISR, user can then be flexible to have a handler or option for a mechanism to alert for missing clock (e.g. - toggle a GPIO to drive a LED to indicate bad clock, or do something else).  In this case, since user probably did not have an MCD handler, clock has defaulted to internal oscillator.

    Regards,

    Joseph