HT85F2270 datasheet(106/226 Pages) HOLTEK

106 / 226 page

Rev. 1.00

106 of ��6

�a� 1�� 01�

Standard 8051 8-Bit Flash MCU

HT85F2260/HT85F2270/HT85F2280

Once an interrupt subroutine is serviced, all the other interrupts must be blocked by clearing

the EAL bit using the application program. This will prevent any further interrupt nesting from

occurring. However, if other interrupt requests occur during this interval, although the interrupt

will not be immediately serviced, the request flag will still be recorded. If an interrupt requires

immediate servicing while the program is already in another interrupt service routine, the EAL bit

should be set after entering the routine, to allow interrupt nesting. If the stack is full, the interrupt

request will not be acknowledged, even if the related interrupt is enabled, until the Stack Pointer is

decremented. If immediate service is desired, the stack must be prevented from becoming full.

When an interrupt request is generated, it takes several instruction cycles before the program jumps

to the interrupt vector.

Wait for � s�stem clocks

�ain

Program

ISR Entr�

…

Enable Bit Set ?

�ain

Program

RETI

(it will set EAL automaticall�)

Automaticall� Disable Interrupt

Clear EAL & Request Flag

Interrupt Request or

Interrupt Flag Set b� Instruction

Interrupt Flowchart

HT85F2270 Datasheet(PDF) 106 Page - Holtek Semiconductor Inc