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AM3354: RTC not starting

Mike Holladay74
Prodigy 130 points

Part Number: AM3354

We are in a pilot production run of a product  that has the Ti AM3354BZCZA100 processor and we are running into a significant percentage of these processors that the RTC intermittently can't be written to successfully and started.  

Digital-Chrysalis# internaltime set 10321520052019
Internal Time Set is 10:32:15 20 05 2019
Digital-Chrysalis#
Digital-Chrysalis#
Digital-Chrysalis#
Digital-Chrysalis# internaltime read
Internal Time is 00:00:00 01 01 2000

  • 0
    TI__Guru**** 393215 points
    Please post details about the RTC - internal/external, crystal, etc... Also post what software and which version you are using.
  • 0 in reply to Biser Gatchev-XID
    Prodigy 130 points

    We are using ThreadX supported base code package not TI's.  The issue us with the internal RTC of the AM3354.    I do remove the bias resistor R8 and it does looks like the  RTC can come up , be set, read and run correctly.  The crystal is for TXC 9HT11 series 12.5pf load capacitance. Either with R8 in place or without I can't see  32.769Khz oscillation  on an oscilloscope even with an active probe.  The data sheet does state "Rbias is not required in most cases". 

  • 0 in reply to Mike Holladay74
    Prodigy 130 points
    I do see the RES_SELECT bit in the RTC_OSC_REG to select internal/external resistor. I am trying to find out how this is set.
  • 0 in reply to Mike Holladay74
    Prodigy 130 points
    We are not setting the RES_SELECT bit in the RTC_OSC_REG register, what does this default to internal bias Resistor ? If set to external is there a recommendation of the external resistor value for the crystal we are using ?
  • 0 in reply to Mike Holladay74
    TI__Guru**** 393215 points
    Please see sections 20.3.5.19 and 20.3.3.2 in the AM335x TRM Rev. P. Clock requirements are given in section 6.2.2.3 of the AM335x Datsheet Rev. K. Also make sure VSS_RTC is connected to common digital GND, as per Errata Advisory 1.0.30.
  • 0 in reply to Biser Gatchev-XID
    Prodigy 130 points

    From coordinating with SW found that we were using the internal PLL to generate the 32.768 KHz. internal to the AM3554.  SW could also set it to function with an external xtal and I could then see the xtal oscillating. 

    Proceeded to look at the RTC reset and found that we were not meeting the requiment given in the data sheet "RTC_PWRONRSTn should be asserted for at least 1 ms to provide enough time for the internal RTC LDO output to reach a valid level before RTC reset is released."  The circuit providing this is a RC  between two Schmidt trigger AND gates were the RC was providing more like .01mSec.  Adjusted values to provide the proper reset to resolve issue.