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.
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,