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TPS929240-Q1: fale safe topic

Kim geng
Prodigy 10 points
Part Number: TPS929240-Q1

Tool/software:

hi team !

for TPS 929240 new version datasheet, i noticed the change point that the "watchdog timer starts to count when uart bus is idle"

plz help give more explain or background information why have such modifications？ 

one more question about applications：

e.g. 2 kinds of different functions used several tps240s and share same uart bus. safety goal: one of function failure not be allowed to influence anothers.

if one of tps240 chip happened failure, controller have to idle whole uart bus, then device can switch to fail-safe mode. in this case another function will be influenced since bus idle. 

is there any suggestion for it? 

  • 0
    TI__Genius 15430 points

    Hi, Kim, 

    We changed watchdog timer counting mechanism comparing to TPS929120 as some users expected. This is the reason having the modification. 

    User may set FORCEFS to 1 if specific device is expected to run into failsafe. If the specific device can receive the massage, TPS929240 will run into failsafe mode directly. If the device can't receive the message due to RX broken, then itself will run into failsafe mode after WDTimer is out. 

    Regards, 

    XG

  • 0 in reply to Xiaoguang1
    Prodigy 10 points

    Hi XG

    thanks for your prompt reply.

    since we can't know which kinds of failure mode happened in advance. so we should consider all scenario or worst case during development phase.  i think RX broken more critical.

    for the RX line broken case, i still confused, basing on latest version datasheet, how WDTimer out? only uart bus "idle". in this case other function will be influenced.  is it correctly?

    i want to know whether have some method to handly it ?(failure function go to fale safe mode, normal function not be influenced)

  • +1 in reply to Kim geng
    TI__Genius 15430 points

    Hi, Kim, 

    If you expect to have devices run into failsafe mode, you can have two ways.  One is keeping BUS idle and not toggling it until timeout. Another way is to write FORCEFS to 1 to specific device and run it into failsafe mode. This won't influent other devices. 

  • 0 in reply to Xiaoguang1
    Prodigy 10 points

    Hi XG,

    got it, 2 ways run into FS mode.

    1. write FORCEFS to device, other function will not be influenced.

    2. keep bus idle until WDTimer out, but unfortunately, other function on same bus will be influenced.

    i think this mechanism really not friendly to some applications. 

    anyways thanks for your excellent support.

    BR