HT46R49 Holtek Semiconductor, HT46R49 Datasheet - Page 35

• Manufacturer Part Number: HT46R49
• Description: Cost-Effective A/D Type 8-Bit MCU
• Manufacturer: Holtek Semiconductor

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related interrupt is enabled, until the Stack Pointer is
decremented. If immediate service is desired, the stack
must be prevented from becoming full.
Interrupt Priority
Interrupts, occurring in the interval between the rising
edges of two consecutive T2 pulses, will be serviced on
the latter of the two T2 pulses, if the corresponding inter-
rupts are enabled. In case of simultaneous requests,
the following table shows the priority that is applied.
These can be masked by resetting the EMI bit.
In cases where both external and internal interrupts are
enabled and where an external and internal interrupt oc-
curs simultaneously, the external interrupt will always
have priority and will therefore be serviced first. Suitable
masking of the individual interrupts using the INTC reg-
ister can prevent simultaneous occurrences.
External Interrupt
For an external interrupt to occur, the global interrupt en-
able bit, EMI, and external interrupt enable bit, EEI, must
first be set. An actual external interrupt will take place
when the external interrupt request flag, EIF, is set, a situ-
ation that will occur when a high to low transition appears
on the INT line. The external interrupt pin is pin-shared
with the I/O pin PA5 and can only be configured as an ex-
ternal interrupt pin if the corresponding external interrupt
enable bit in the INTC register has been set. The pin must
also be setup as an input by setting the corresponding
PAC.5 bit in the port control register. When the interrupt is
enabled, the stack is not full and a high to low transition
appears on the external interrupt pin, a subroutine call to
the external interrupt vector at location 04H, will take
place. When the interrupt is serviced, the external inter-
rupt request flag, EIF, will be automatically reset and the
EMI bit will be automatically cleared to disable other inter-
rupts. Note that any pull-high resistor configuration op-
tions on this pin will remain valid even if the pin is used as
an external interrupt input.
Rev. 1.30
External Interrupt
Timer/Event Counter Overflow
A/D Converter Interrupt
Interrupt Source
All Devices Priority
1
2
3
Interrupt Structure
HT46R46/C46/R47/C47/R48A/C48A/R49
35
Timer/Event Counter Interrupt
For a Timer/Event Counter interrupt to occur, the global
interrupt enable bit, EMI, and the corresponding timer
interrupt enable bit, ETI, must first be set. An actual
Timer/Event Counter interrupt will take place when the
Timer/Event Counter request flag, TF, is set, a situation
that will occur when the Timer/Event Counter overflows.
When the interrupt is enabled, the stack is not full and a
Timer/Event Counter overflow occurs, a subroutine call
to the timer interrupt vector at location 08H, will take
place. When the interrupt is serviced, the timer interrupt
request flag, TF, will be automatically reset and the EMI
bit will be automatically cleared to disable other inter-
rupts.
A/D Interrupt
For an A/D interrupt to occur, the global interrupt enable
bit, EMI, and the corresponding interrupt enable bit,
EADI, must be first set. An actual A/D interrupt will take
place when the A/D converter request flag, ADF, is set, a
situation that will occur when an A/D conversion process
has completed. When the interrupt is enabled, the stack
is not full and an A/D conversion process finishes exe-
cution, a subroutine call to the A/D interrupt vector at lo-
cation 0CH, will take place. When the interrupt is
serviced, the A/D interrupt request flag, ADF, will be au-
tomatically reset and the EMI bit will be automatically
cleared to disable other interrupts.
Programming Considerations
By disabling the interrupt enable bits, a requested inter-
rupt can be prevented from being serviced, however,
once an interrupt request flag is set, it will remain in this
condition in the INTC register until the corresponding in-
terrupt is serviced or until the request flag is cleared by a
software instruction.
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 con-
trolled, the original control sequence will be damaged
once a CALL subroutine is executed in the interrupt
subroutine.
June 5, 2008