HT85F2260 Datasheet, PDF (117/226 Pages) Holtek Semiconductor Inc – Standard 8051 8-Bit Flash MCU

Standard 8051 8-Bit Flash MCU
HT85F2260/HT85F2270/HT85F2280
Interrupt Wake-up Function
Each of the interrupt functions has the capability of waking up the microcontroller when in the
IDLE mode, and only INT0 and INT1 interrupts can wake up the microcontroller when in the
Power-down 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 Power-Down or IDLE Mode and the CPU clock 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 Power-Down or IDLE Mode. The interrupt enable bits have no
effect on the interrupt wake-up function.
Programming Considerations
By disabling the 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.
It is recommended that programs do not use the “CALL subroutine” instruction within the interrupt
subroutine. Interrupts often occur in an unpredictable manner or need to be serviced immediately
in some applications. 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.
All these interrupt functions have the capability of waking up the microcontroller when in
the IDLE mode, only INT0 and INT1 interrupts can wake up the microcontroller when in the
Power-down mode.
Only the Program Counter is pushed onto the stack. If the contents of the register or status register
are altered by the interrupt service program, which may corrupt the desired control sequence, then
the contents should be saved in advance.
Rev. 1.00
117 of 226
May 15, 2013