RESET pin sometimes doesn’t have any effect.

10 thoughts on “RESET pin sometimes doesn’t have any effect.

  1. Hi

     

    I have UL865-EUD and sometimes it goes into a state of no response. CTS stays high and PWRMON is up. Supply voltage is 3.3 V. That would be OK if I could reset it, but reset pin in this situation doesn’t help either. Usually I keep it low for 300 ms but I tried also different delays, no luck. Only full power cycle helps, and that solves the problem every time. What can be the issue?

     

    HW guide says: "the transistor must be connected as close as possible to the RESET* pin." – why is that exactly? In our case the line on PCB is 28,5 mm x 0,25 mm – is that bad?

     

    Update: Now I managed to break the module so that even full power cycle doesn’t fix it. But all the pin values are still the same: PWRMON is 1,8 V and CTS is always 1,8 V. 

     

    Regards

    Lauri 

  2. This
    kind of issue isn’t so simple to be managed by the Forum Telit, it
    would be better that customer will contact ts-emea@telit.com.

    For example we need to check the schematic, then maybe it would be required a RTD trace acquisition.

    However,
    a test that customer could execute is testing the module by a nominal
    Power Supply voltage (3.8V) and observing if the bad behavior disappear.

    1. Thank you, we will try that an see.

       

      But I have one related question. What if the module is shut down or it has performed low voltage shutdown. How can it be turned on again? Will the RESET pin initiate "power on sequence" or is it always needed to power-cycle the module?

       

      Regards

      Lauri

        1. Hi

           

          I’m sorry, can you be a bit more specific?

           

          I rely on the HW guide [1] that has the followign chapters:

           

          5.1. Auto-Turning ON the UL865
          5.2. Turning OFF the UL865

           

          They don’t explicitly state the case when module has shut down itself. Nor the question if RESET pin (or any other) can be used to start the module again.

           

          If you are referring to the "Turning OFF" sequence, where power is disconnected after shutdown, does that mean that power supply disconnecting possibility should be designed on PCB? Otherwise there can a dead-lock situation where module is shut down but MCU cannot start is again?

           

          Regards

          Lauri 

          [1] Telit_UL865_Hardware_User_Guide_r5

          1. The module will start again if power voltage is mantained say after an AT#SHDN is performed, or hard RESET ; if power is removed re-aplying it makes the modulel also start. As said the RESET line must be used only as a last recovery option and kept released (open collector transistor, not pullup transistor or totem pole output).

             

            Indeed if your project needs to keep the module power-off, maybe because the module’s power saving options still present too much power usage, you will need to implement a way to remove the power from the module.

             

          2. Hi

             

            Thank you. So the AT#SHDN command on UL865 is useful only if power is disconnected after last OK response? Otherwise the module will start again?

             

            And in my case, if module doesn’t respond but power is above 3.4 V, there must be something really wrong because the module cannot be just shut down when supply voltage is applied?

             

            A few observations regarding that:

             * HW Guide mentions "AT#SYSHALT" command (chapter 5.2) but AT Command Reference doesn’t list it. There is a AT#SHDN instead, like you mentioned.

            * AT Command Reference mentions "Note: to turn it on again Hardware pin ON/OFF must be tied low." but that I guess doesn’t exists on UL865. Though there is a small remark about that pin on page 47 of the HW guide.

             

            Rgerdas

            Lauri 

          3. Check AT#SYSHALT availability on your firmware with AT#SYSHALT=?. On GL865 platform this command indeed shuts off the module regardless of the power voltage presence.

             

            And in my case, if module doesn’t respond but power is above 3.4 V,
            there must be something really wrong because the module cannot be just
            shut down when supply voltage is applied?

             This is a case for RESET isn’t it?

             

  3. This is a case for RESET isn’t it? 

     

     Yes, sometimes it seems that RESET doesn’t help and I was wondering if the module can be in "shut down" mode so that only a special pin or action (power-cycle) will turn it on again. But I think I got my answer that "normally" there should not be such a situation? We haven’t designed disconnecting power from Telit module, but if this is needed for power-cycle (to turn the module on again on rare cases) we would need to design it.

     

    Check AT#SYSHALT availability on your firmware with AT#SYSHALT=?. On GL865 platform this command indeed shuts off the module regardless of the power voltage presence. 

     

    OK, I will try that command later today. I don’t use it, but if this command is performed, does that mean that power cycle must be carriet out to turn the module on again, or should RESET pin do the work? And what if Telit module turns itsef off (for example, because of low voltage or brown-out). Will it turn itself on again after a while?

    1. Hi Lauri,

       

      Since the RESET pin should be used only for emergency case, and since UL865 will

      self turn ON after a AT#SHDN or VBAT removing and re insertion, so we developped the SYSHALT command in order to "freeze" the module.

      After module entered in this Hybernate status you can remove the VBat safely, otherwise, removing power supply while SW is running could lead to a flash memory corruption and in this case you need to reprogramm it.