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AM3359 & TPS3823

michael musset
Expert 1135 points

Other Parts Discussed in Thread: TPS3823

Hi,

In my project I'm using the TPS3823 has a watchdog. The WDI signal is connected to GPIO2_3 ( T7 ) .

The problem is that when the board boot, the watchdog reset the board before the processor has the time to boot ... I didn't put any pull up or pull down resistor on the line . I have tried also with GPIO 1_15. But got the same result.

I think that GPIO2_3 is used at boot, but GPIO 1_15, I dont think that it's used at boot ... I'm sure that It's in high impedance.

The Yellow signal is the VDD.

The blue signal is the WDI.

The purple signal is the Reset signal ....

We can see that the component tps3823 try to determin if the input is in high impedance, but for some reason it detect that it's not .... Something is wrong with my way of understanding ?

  • 0
    Expert 1135 points

    Edit :  It's the TPS3823 that I use .... 

  • 0 in reply to michael musset
    TI__Guru**** 393215 points
    Hi,

    According to the TPS3823 datasheet WDI must be high-impedance in order to be ignored. GPIO 1_15 and GPIO2_3 are high-impedance at reset release time, but they have internal pullup, resp. pulldown enabled which defined the input level at WDI. Both of these pins will also be configured by ROM code if GPMC is involved in the boot sequence.
  • 0 in reply to michael musset
    Expert 1135 points
    I've posted a new topic in the correct forum :

    e2e.ti.com/.../508516
  • 0 in reply to Biser Gatchev-XID
    Expert 1135 points
    Ok, The boot sequence of the processor ( configured by sysboot ) is :

    MMC1, MMC0, UART0, USB0

    I'm doing the test without any eeprom/sdcard to boot on .... so the processor is in the state of waiting to boot .

    From the Table 26-28 of the documentation, it gives the pin used at boot for mmc0/1 .

    Normally GPIO1_15 = GPMC_AD15 ( signal name ) is not used at boot, so GPIO1_15 has be in high impedance mode, but for some reason, it's not. Or I'm not using the correct watchdog.
  • 0 in reply to michael musset
    TI__Guru**** 393215 points

    michael musset said:
    I'm doing the test without any eeprom/sdcard to boot on .... so the processor is in the state of waiting to boot .

    This is not correct. The processor is cycling through the boot devices continuously. Not important for this case though.

    michael musset said:
     Normally GPIO1_15 = GPMC_AD15 ( signal name ) is not used at boot, so GPIO1_15 has be in high impedance mode, but for some reason, it's not.

    It is high-impedance, however it has an internal pulldown resistor enabled. If you look at Table 4-1 from the AM335X Datasheet Rev. J you will see that state at reset release time is L: High-impedance with an active pulldown resistor.