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TMS320VC5507: power-up reset and CLKOUT behavior

Koichiro Tashiro
Mastermind 22945 points
Part Number: TMS320VC5507

Hi,

I got a question from my customer about power-up reset timing.
According to datasheet (SPRS244J), Figure 5-15 or Figure 5-16, 
CLKOUT should be active before nRESET is released(high).

But my customer observed CLKOUT is not active during nRESET is active(low).
CLKOUT is on 2.7usec after nRESET is released.
Please see attached waveform.
Is this datasheet bug?
DSP_Reset.pdf



By the way, datasheet section 5.6.1 says the internal oscillator is always enabled after device reset.

If so, Figure 5-16 condition (On-Chip Oscillator Inactive) never happens, correct?


Thanks and regards,
Koichiro Tashiro

  • 0
    TI__Mastermind 29408 points

    Hi,

    I'm looking into this issue and will respond early next week.

    Regards,
    Frank

  • 0 in reply to Frank Livingston
    TI__Mastermind 29408 points

    Hi,

    Sorry for the delayed response.

    Koichiro Tashiro said:
    If so, Figure 5-16 condition (On-Chip Oscillator Inactive) never happens, correct?

    The oscillator is always enabled according to the datasheet, 3.5.1 External Bus Selection Register (EBSR). I think Figure 5-16 is showing the case of the X1 oscillator output not being connected to an external crystal.

    Koichiro Tashiro said:
    Is this datasheet bug?

    Please see TMS320C55x DSP Peripherals Overview (spru317k.pdf), 3.7.1 Clock Generator During Reset.

    The DSP can make use of the output clock signal during reset. While the DSP reset signal is held low, he clock generator is in the bypass mode, so CLKOUT should have the same frequency as CLKIN.

    I don't think the description of the CLKMD input pin is correct since I don't see any reference to
    this pin in the datasheet. Likely this is tied low internally on C5507.

    In Table 2−3. Signal Descriptions, I see CLKOUT goes into high-impedance state when nOFF is driven low. What are the nTRST & EMU/nOFF signals in the customer setup before nRESET is pulled high?

    Regards,
    Frank

  • 0 in reply to Frank Livingston
    TI__Mastermind 22945 points

    Hi Frank,

    So you meant the waveforms customer observes are not expected. CLKOUT should be active before nRESET is released.

    Frank Livingston said:
    What are the nTRST & EMU/nOFF signals in the customer setup before nRESET is pulled high?

    At that timing, nTRST is Low(PD to GND) and EMU/nOFF is 3.3V(PU to I/O power rail).
    Then CLKOUT is not in high-impedance state.

    Thanks and regards,
    Koichiro Tashiro