ht82k74e Holtek Semiconductor Inc., ht82k74e Datasheet - Page 25

• Manufacturer Part Number: ht82k74e
• Description: 27mhz Keyboard/ Mouse Tx 8-bit Mcu
• Manufacturer: Holtek Semiconductor Inc.

Timer/Event Counter Interrupt
For a Timer/Event Counter interrupt to occur, the global
interrupt enable bit, EMI, and its corresponding timer in-
terrupt 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.
Programming Considerations
By disabling the interrupt enable bit, the requested inter-
rupt can be prevented from being serviced, however,
once an interrupt request flag is set, it will remain in this
Rev. 1.00
Interrupt Control Register
25
condition in the interrupt control register until the corre-
sponding interrupt 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.
All of these interrupts have the capability of waking up
the processor when in the Power Down Mode.
Only the Program Counter is pushed onto the stack. If
the contents of the accumulator or status register are al-
tered by the interrupt service program, which may cor-
rupt the desired control sequence, then the contents
should be saved in advance.
HT82K74E/HT82K74EE
December 15, 2009