MPC860TZQ80D4

[danybourget]

We've been using the MPC860TZQ80D4 for many years in one of our product without having any trouble. Now we have two boards with the same problem. When I power up the unit the first time, everything works fine. After 1 minute, if I power down the unit and then power it up the MPC860TZQ80D4 stuck in an infinite loop (time base instruction). If I compare the EXTCLK with the CLKOUT I could see a phase shift (see attachment). Could it be a PLL problem? If I place a 8pF scope probe on the EXTCLK signal the processor starts correctly every single time.

[danybourget]

If I slightly reduce the fall time of the EXTCLK, the board seems to work. Does anyone know the EXTCLK characteristics (min max frequency, edge, voltage...)

[alexander_yakov]

The EXTCLK input frequency range is specified from 15 Mhz to maximum operating frequency of the device. The maximum slew rate is not limited in the documentation, however faster slew rate typically lead to much noise, which in turn causes PLL unstability. Maximum EXTCLK input voltage is specified as VDD+0.3V

Have a great day,
Alexander

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