HT68F14 HOLTEK [Holtek Semiconductor Inc], HT68F14 Datasheet - Page 117

• Manufacturer Part Number: HT68F14
• Description: Enhanced I/O Flash Type MCU
• Manufacturer: HOLTEK [Holtek Semiconductor Inc]

Rev. 1.10
Interrupt Wake-up Function
Programming Considerations
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 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, a low power supply voltage or comparator input change may cause their
respective interrupt 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 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.
By disabling the relevant interrupt enable bits, a requested interrupt can be prevented from being
serviced, however, once an interrupt request flag is set, it will remain in this condition in the interrupt
register until the corresponding interrupt is serviced or until the request flag is cleared by the
application program.
Where a certain interrupt is contained within a Multi-function interrupt, then when the interrupt
service routine is executed, as only the Multi-function interrupt request flags, MF0F~MF1F, will be
automatically cleared, the individual request flag for 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 SLEEP or IDLE
Mode, the wake up being generated when the interrupt request flag changes from low to high. If it is
required to prevent a certain interrupt from waking up the microcontroller then its respective 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.
117
Enhanced I/O Flash Type MCU
HT68F13/HT68F14/HT68F15
February 9, 2011