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TMS320c6678 RESETFULL and power-on

Bruno B
Expert 1290 points

Other Parts Discussed in Thread: TMS320C6678

hi,

I have ONE question about the TMS320C6678 configuration at power-up.

THe datasheet (SPRS691D April 2013) fig 7.1 shows that the RESETFULL rising_edge functionaly samples the GPIO configuration bits.

But page 133 - §7.4.1 , it is written that " 4. The POR pin can now be de-asserted. Reset sampled pin values are latched at this point"

This is quite confusing because I am interpreting "Reset sample pins" as the "GPIO configuration pins". ANd in that case, that would mean that configuration is now determined
upon the POR risin_edge .

What should we understand really? and what is the meaning of "Reset sampled pin" ? compared to "GPIO configuration" pins.


I have also a 2nde question about RESETFULL which is ONLY mentionned during the power-on sequence (not mentionned during "hard reset" §, nor during "soft reset" §, nor during "local reset" § )
However the fig 7.4 shows a case where RESETFULL has been activated, and this does not correspond to a power-up.
==> Therefore, what is the situation corresponding to fig.7.4 ? and what is the consequences of RESETFULL being activated in such a way ?

With best regards,

Bruno

  • 0
    TI__Mastermind 30825 points

    Brune,

    Figure 7.1 is the power up sequence of the device.  It requires the use of RESETFULLz.

    Page 133, is referring to applying a PORz reset after the device has been powered up and does not require a RESETFULLz (i.e. may apply PORz pin only.)  In this case the GPIO Configuration pins are sampled (i.e. these are the pins that are being referred to) when the PORz is deasserted.

    Applying RESETFULLz is only required during power up sequence, and it may be used optionally for a Power on Reset, but should not be used during Hard, Soft or Local Resets.

    Please not that a Power On Reset is not the power up sequence, but is the same level of a reset as powering up the device, only w/o a power up sequence being required as the device has already gone through the power up sequence.

    Best Regards,

    Chad

  • 0 in reply to Chad Courtney
    Expert 1290 points

    Hi Chad,

    Thank you for your support.

    I am sorry to tell you that still not understand everything.

    - You are explaining that page 133 applies AFTER the device has already been powered-up. This is also confirmed at the beginning of the paragraph : see : "The assumption is that, device is already powered up".

    BUT if you read the step 3, it is written that "POR must be held active until all supplies on the board are stable ...". This formulation lets me think that the power IS currently BEING applied and is still not established.
    ==> Therefore I would say that the sequence is more describing a Power-up. All this is quite confusing for me. Can you clarify more that ambiguous point ?

    - Another trouble is that RESETFULL is described at the beginning as a potential initiator of the Power-on sequence, but it never appears during the steps 1,2,3,4,5,6.

    - Should we simply assume that at any time after power-up, it is allowed to initiate a power-on sequence, just by activating RESETFULL as described in fig 7.4, without using PORz pin at all ?

    Best regards,

    Bruno

  • 0 in reply to Bruno B
    TI__Mastermind 30825 points

    It's not describing a power up, but during a POR, it can have the rails be unstable, sometimes customers need to bring rails down for other HW, this is not a requirement to do a POR, but if it is done, there are requirements for the POR.

    Again, RESETFULLz is only required for the initial power up sequence, which this is not describing.

    You can apply a power on reset w/ only the RESTFULLz after the device has fully been powered up as described.  If some of the rails need to come down for some reason, then you'll need to use the PORz though.

    Best Regards,

    Chad

  • 0 in reply to Chad Courtney
    Expert 1290 points

    Hi Chad,

    This is what I can understand from your answer :

    a) If I need for some reason to power-down one rail, then I must activate POR and follow the steps from page 133. Is this correct ?

    b) If so, that's means that a very new information from you is that it is possible to power-down one single rail, without having to power-down EVERY rails (in the reverse order of the power-up). Is this correct ?

    This sounds quite strange, because I would have considered this situation as a power failure, and issued a POWER-DOWN sequence.

    c) In that case, POR must be activated, then the single rail re-applied , and then the POR de-activated (roughly). All without any use of RESETFULL. Is this correct ?

    d) During normal operation (DSP executing software), I can command a POR(function described in table 7.9)  by only activating the RESETFULL, and waiting for RESETSTAT Is this correct ?

    Bruno