AN977 Datasheet, PDF (12/17 Pages) STMicroelectronics – GUIDELINES FOR UPGRADING FROM THE ST92F120

GUIDELINES FOR UPGRADING FROM THE ST92F120 (0.50 µm) TO THE ST92F124...
2.4.2 PLL
2.4.2.1 Standard Mode
The reset value of the PLLCONF register (p55, R246) will start the application in the same way
as in the ST92F120. To use free running mode in the conditions described in Section 1.5, the
PLLCONF[7] bit must be set.
2.4.2.2 Safety Clock Mode
Using the ST92F120, if the clock signal disappears, the ST9 core and peripheral clock is
stopped, nothing can be done to configure the application in a safe state.
The ST92F124/F150/F250 design introduces the safety clock signal, the application can be
configured in a safe state.
When the clock signal disappears (for instance due to a broken or disconnected resonator),
the PLL unlock event occurs.
The safer way to manage this event is to enable the INTD0 external interrupt and to assign it
to the RCCU by setting the INT_SEL bit in the CLKCTL register.
The associated interrupt routine checks the interrupt source (refer to the 7.3.6 Interrupt Gen-
eration Chapter of the ST92F124/F150/F250 datasheet), and configures the application in a
safe state.
Note: The peripheral clock is not stopped and any external signal generated by the microcon-
troller (for instance PWM, serial communication...) must be stopped during the first instruc-
tions executed by the interrupt routine.
2.5 EXTENDED FUNCTION TIMER
2.5.1 Input Capture / Output Compare
In order to generate a Timer Interrupt, a program developed for the ST92F120 may need to be
updated in certain cases:
– If Timer Interrupts IC1 and IC2 (OC1 and OC2) are both used, ICIE (OCIE) of register CR1
has to be set. The value of the IC1IE and IC2IE (OC1IE and OC2IE) in the CR3 register is
not significant. So, the program does not have to be modified in this case.
– If only one Interrupt is needed, ICIE (OCIE) must be reset and IC1IE or IC2IE (OC1IE or
OC2IE) must be set depending on the interrupt used.
– If none of the Timer Interrupts are used, ICIE, IC1IE and IC2IE (OCIE, OC1IE and OC2IE)
they must all be reset.
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