Controller working after crstal failure in MKE04Z64VLH4

[prasannanaik]

Hi,

   I am using MKE04Z64VLH4 in a product.I am operating the microcontroller in FEE mode with 8 MHz crystal stepped up using FLL to 40 MHz . I am using PIT module to generate a 625 usec delay and toggling a port pin in PIT interrupt. While testing the behaviour of product on crystal failure, i had following strange observations:

1) Microcontroller operates even when crystal has been disconnected (Does it switch automatically to internal FEI mode or something?)

2) The 625 usec delay becomes 712 usec on crystal disconnection.

Test Process:

1) The crystal was disconnected by connecting one leg of crystal to a jumper and disconnecting that jumper in run time (Not an ideal way to connect crystal but i wanted to test it)

2) Measure 625 usec pulse on a Digital Storage Oscilloscope to check the state of microcontroller (Should be Idle when controller becomes dead)

Thanks and best regards,

Prasanna

[vicentegomez]

Hi

If you are not setting the loss of clock interrupt, the PLL can continue working but it can lose the signal easily, I have done the same on other devices with the same ICS module and some of them works some minutes, some of them works just for a few seconds, If you use the  loss-of-clock interrupt you can detect this problem

Regards

Vicente Gomez

[prasannanaik]

Hi Vicente,

     Thanks for the reply, in our application we have enable the loss of clock interrupt but after disconnecting the crystal microcontroller still works same as before. I have kept it for 3 hours approximately but PLL does bot loses its signal and no interrupt came for loss of clock. PIT module still toggles the port pin in its PIT interrupt  In any case it is possible and How?

Thanks and best regards

Prasanna

[mjbcswitzerland]

Hi

The ICS in the KE04 doesn't have a PLL, but instead just the FLL. The FLL will continue oscillating even if its external reference is removed (which it locks its frequency too and doesn't derive its frequency from) but will oscillate at its natural rate rather than being locked to the reference.

Check the details about the lock and and loss of lock flags to check that they are reacting as expected:

Regards

Mark

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