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HT66FM5440
Brushless DC Motor A/D Flash MCU
HT66FM5440
Brushless DC Motor A/D Flash MCU
Interrupt Wake-up Function
Each of the interrupt functions has the capability of waking up the microcontroller when in the
SLEEP or IDLE Mode. A wake-up is generated when an interrupt priority request flag changes
from low to high and is independent of whether the interrupt is enabled or not. Therefore, even
though the device is in the SLEEP or IDLE Mode and its system oscillator stopped, situations such
as external edge transitions on the external interrupt pins or a low power supply voltage may cause
their respective interrupt priority request flag to be set high and consequently generate an interrupt.
Care must therefore be taken if spurious wake-up situations are to be avoided. If an interrupt wake-
up function is to be disabled then the corresponding interrupt priority request flag should be set high
before the device enters the SLEEP or IDLE Mode. The interrupt enable bits have no effect on the
interrupt wake-up function.
Programming Considerations
By disabling the relevant interrupt enable bits, a requested interrupt can be prevented from being
serviced. Where a certain interrupt, whether has its own request flag or not, has been configured to
an interrupt priority level, then when the interrupt service routine is executed, as only the interrupt
priority request flags, Int_prinF, will be automatically cleared, the individual request flag of the
function needs to be cleared by the application program.
It is recommended that programs do not use the "CALL" instruction within the interrupt service
subroutine. Interrupts often occur in an unpredictable manner or need to be serviced immediately.
If only one stack is left and the interrupt is not well controlled, the original control sequence will be
damaged once a CALL subroutine is executed in the interrupt subroutine.
Every interrupt has the capability of waking up the microcontroller when it is in the SLEEP or IDLE
Mode, the wake up being generated when the relevant interrupt priority request flag changes from
low to high. If it is required to prevent a certain interrupt from waking up the microcontroller then its
respective interrupt priority request flag should be first set high before enter SLEEP or IDLE Mode.
As only the Program Counter is pushed onto the stack, then when the interrupt is serviced, if the
contents of the accumulator, status register or other registers are altered by the interrupt service
program, their contents should be saved to the memory at the beginning of the interrupt service routine.
To return from an interrupt subroutine, either a RET or RETI instruction may be executed. The RETI
instruction in addition to executing a return to the main program also automatically sets the EMI bit high
to allow further interrupts. The RET instruction however only executes a return to the main program
leaving the EMI bit in its present zero state and therefore disabling the execution of further interrupts.