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Original question:

F28069 Reset pulse duration

TMS320F28054F: XRS pulse duration on warm reset?

SY Yoon
Genius 3380 points
Other Parts Discussed in Thread: TMS320F28054F

Hello,

TMS320F28054F resets when there is noise on the XRS pin.

I checked the pulse duration of XRS on warm reset in the datasheet. 

But this condition doesn't fit my case. 

The noise is shorter than the pulse duration.

Does device reset even in low that is shorter than pulse duration?

  • 0
    TI__Guru* 95315 points

    You have neither indicated the width of the noise pulse nor the frequency of the input clock. The parameter shown in the datasheet is the minimum pulse width needed to ensure a reliable reset every time. This does not, however, mean that a smaller pulse will not cause a reset.

  • 0 in reply to Hareesh Janakiraman
    Genius 3380 points

    Hi, 

    I'm using the internal oscillator.

    The width of the noise is about a few tens of ns.

    This is much shorter than the pulse duration 600us.

  • 0 in reply to SY Yoon
    TI__Guru* 95315 points

    Could you please attach an oscilloscope capture of the pulse at -XRS pin? I need the precise width of the pulse, not an estimate. 

    This is much shorter than the pulse duration 600us.

    You should be looking at Table 5-3, not 5-4. The number that is applicable in your situation is tw(RSL2).

     

  • 0 in reply to Hareesh Janakiraman
    Genius 3380 points

    Sorry, I made a mistake.

    I use the 20MHz external crystal.

    And  the pulse duration means tw(RSL2) I said.

    I said wrong.

    I'm going to attach an oscilloscope capture ASAP.

  • 0 in reply to SY Yoon
    Genius 3380 points

    Hi, 

    I attach an oscilloscope capture.

    I made LOW signal for reset test.

    Reset occurred from 230ns of LOW signal.

    tw(RSL2) is 32tc(OSCCLK) in datasheet. And OSCCLK is 20MHz.

    The pulse duration can be calculated as 1.6us. Is it right? 

    I'm asking why the reset occurs at a duration is shorter than tw(RSL2).

  • 0 in reply to SY Yoon
    TI__Guru* 95315 points

    You are correct about 1.6 uS. There is a glitch filter on the -XRS pin that filters glitches smaller than 200 ns. So, any pulse wider than 200 ns will be able to assert a reset. The datasheet number is a conservative number with added margin. This margin is added to ensure that the quoted number [32 tc(OSCCLK) ] will assert a reset under all conditions (voltage/temperature extremes).