HT68F04 Holtek Semiconductor, HT68F04 Datasheet - Page 112

• Manufacturer Part Number: HT68F04
• Description: Small Package Enhanced Flash Type 8-Bit MCU
• Manufacturer: Holtek Semiconductor

Interrupt Operation
When the conditions for an interrupt event occur, such
as a TM Comparator P, Comparator A or Comparator B
match or A/D conversion completion etc, the relevant in-
terrupt request flag will be set. Whether the request flag
actually generates a program jump to the relevant inter-
rupt vector is determined by the condition of the interrupt
enable bit. If the enable bit is set high then the program
will jump to its relevant vector; if the enable bit is zero
then although the interrupt request flag is set an actual
interrupt will not be generated and the program will not
jump to the relevant interrupt vector. The global interrupt
enable bit, if cleared to zero, will disable all interrupts.
When an interrupt is generated, the Program Counter,
which stores the address of the next instruction to be ex-
ecuted, will be transferred onto the stack. The Program
Counter will then be loaded with a new address which
will be the value of the corresponding interrupt vector.
The microcontroller will then fetch its next instruction
from this interrupt vector. The instruction at this vector
will usually be a ²JMP² which will jump to another sec-
tion of program which is known as the interrupt service
routine. Here is located the code to control the appropri-
ate interrupt. The interrupt service routine must be ter-
minated with a ²RETI², which retrieves the original
Program Counter address from the stack and allows the
microcontroller to continue with normal execution at the
point where the interrupt occurred.
Rev. 1.00
112
HT66F03/HT66F04/HT68F03/HT68F04
The various interrupt enable bits, together with their as-
sociated request flags, are shown in the accompanying
diagrams with their order of priority. Some interrupt
sources have their own individual vector while others
share the same multi-function interrupt vector. Once an
interrupt subroutine is serviced, all the other interrupts
will be blocked, as the global interrupt enable bit, EMI bit
will be cleared automatically. This will prevent any fur-
ther interrupt nesting from occurring. However, if other
interrupt requests occur during this interval, although
the interrupt will not be immediately serviced, the re-
quest flag will still be recorded.
If an interrupt requires immediate servicing while the
program is already in another interrupt service routine,
the EMI bit should be set after entering the routine, to al-
low interrupt nesting. If the stack is full, the interrupt re-
quest will not be acknowledged, even if the related
interrupt is enabled, until the Stack Pointer is decre-
mented. If immediate service is desired, the stack must
be prevented from becoming full. In case of simulta-
neous requests, the accompanying diagram shows the
priority that is applied. All of the interrupt request flags
when set will wake-up the device if it is in SLEEP or
IDLE Mode, however to prevent a wake-up from occur-
ring the corresponding flag should be set before the de-
vice is in SLEEP or IDLE Mode.
April 16, 2010
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