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F28M36P63C2: Standalone speed slower than with emulator

KarlheinzRieber
Intellectual 550 points
Part Number: F28M36P63C2

Hello,

I have a custom board with the F28M36P63C2 and an external crystal of 20MHz. If I run the blinky example (start by the V2 emulator) then the blinking frequency is about 600 kHz. Running the same software without emulator (standalone), then the blinking is only about 60kHz. So the execution speed seems 10 times slower.

Can it be something with the clock detection? Measuring the crystal shows that it has a stable 20 MHz. Does it probably take to long to start the crystal in standalone mode? We have the slow speed on 3 boards out of 20. The rest run fine...


Any hints are welcome.


Thank you very much,

Karlheinz

  • 0
    TI__Expert 8105 points
    Karlheinz,

    Please check for the missing clock status bit, you can drive it out to a GPIO and observe it for the failing boards. If the PLL cannot lock using external osc/xtal the chip switches to internal oscillator to drive the clock. This is most likely explanation for what you are seeing.

    Regards,
    PEter
  • 0 in reply to Peter Galicki
    Intellectual 550 points

    Hello Peter,

    yes, it seems to be the missing clock.

    The clock itself is running with 20 MHz, so I guess it takes to long to start up.

    What can by my options?

    Must I change the hardware? I have a RC-combination at XRS and ARS with 2.2k and 100nF. Does it help to increase these values? I already replaced the resonator by a different one, without success.

    I am responsible for the software, but I guess software could offer a solution as well. Any suggestions I can pass to the software guy?

    Thanks a lot,

    Karlheinz

  • 0 in reply to KarlheinzRieber
    Intellectual 550 points

    Hello,

    I read in the errata datasheet that there are some differences in the revisions of the F28M36. Unfortunately we have revision B assembled. Therefore this table of ESR values in the errata datasheet is needed.

    Unfortunately we have an ESR of 50 Ohms at 20 MHz, therefore we can not reach the given values of 15 and 30 Hz.

    How long have been the revision B sold? As there already revision E and F on the market, I guess our F28M36 are not brandnew....

    Is there still a chance to restart the PLL with the external crystal by software?

    Thank you very much for your answers,

    Karlheinz