HT68F03 datasheet(119/139 Pages) HOLTEK

119 / 139 page

HT66F03/HT66F04/HT68F03/HT68F04

Rev. 1.00

119

April 16, 2010

Programming Considerations

By disabling the relevant interrupt enable bits, a re-

quested interrupt can be prevented from being serviced,

however, once an interrupt request flag is set, it will re-

main 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, MFnF, 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

²CALL²

instruction within the interrupt service subroutine. Inter-

rupts 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 se-

quence will be damaged once a CALL subroutine is exe-

cuted 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 al-

tered 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.

HT68F03 Datasheet(PDF) 119 Page - Holtek Semiconductor Inc

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