SPRZ545C July 2023 – March 2024 TMS320F28P650DH , TMS320F28P650DK , TMS320F28P650SH , TMS320F28P650SK , TMS320F28P659DH-Q1 , TMS320F28P659DK-Q1 , TMS320F28P659SH-Q1
MCD: Missing Clock Detect Should be Disabled When the PLL is Enabled (PLLCLKEN = 1)
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The PLL has a limp mode feature to provide a slow PLLRAWCLK output even if its input OSCCLK is absent. Independently, the Missing Clock Detect (MCD) circuit will forcibly switch the system clock source to INTOSC1 when a missing OSCCLK input is detected. The MCD mux to switch between these system clock sources is not ensured to be glitch-free when both clock sources (PLLRAWCLK and INTOSC1) are still active. In rare cases, this may lead to unpredictable device behavior during a missing clock failure event.
When the PLL is used by the system (PLLCLKEN = 1), disable the MCD by writing MCDCR.MCLKOFF = 1.
The Dual Clock Comparator (DCC) circuit can be configured to quickly detect if the SYSCLK frequency drops outside the desired frequency to its limp mode due to a missing clock event.
When the system is operating in PLL bypass mode (PLLCLKEN = 0), the MCD circuit can still be used to detect missing clock events and switch the clock source to INTOSC1.