
Interrupt Control Unit
7-27
7.3.13
End-of-Interrupt Register
(EOI, Offset 22h)
(Master Mode)
The End-of-Interrupt (EOI) register is a write-only register. The in-service flags in the In-
Service register (see Section 7.3.8 on page 7-22) are reset by writing to the EOI register.
Before executing the IRET instruction that ends an interrupt service routine (ISR), the ISR
should write to the EOI register to reset the IS bit for the interrupt.
The specific EOI reset is the most secure method to use for resetting IS bits. Figure 7-16
shows example code for a specific EOI reset. See Table 7-1 on page 7-4 for specific EOI
values.
Figure 7-16
Example EOI Assembly Code
Figure 7-17
End-of-Interrupt Register
Bit 15: Non-Specific EOI (NSPEC)—The NSPEC bit determines the type of EOI command.
When written as a 1, NSPEC indicates non-specific EOI. When written as a 0, NSPEC
indicates the specific EOI interrupt type is in S4–S0.
Bits 14–5: Reserved
Bits 4–0: Source Interrupt Type (S4–S0)—Specifies the EOI type of the interrupt that is
currently being processed. See Table 7-1 on page 7-4.
...
...
;ISR code
...
exit:
mov ax,int_type
;load the interrupt type in ax
mov dx, 0ff22h
;write the interrupt type to EOI
out dx,ax
popa
iret
;return from interrupt
15
7
0
S4–S0
NSPEC
Reserved
Содержание Am186 ES
Страница 1: ...Am186 ES and Am188 ES User s Manual...
Страница 4: ...iv...
Страница 12: ...Table of Contents xii...
Страница 22: ...Features and Performance 1 8...
Страница 60: ...System Overview 3 28...
Страница 84: ...Chip Select Unit 5 14...
Страница 132: ...Timer Control Unit 8 8...
Страница 166: ...Programmable I O Pins 11 6...
Страница 184: ...Register Summary A 18...