IBM AT 5170 Technical Reference page 36

Linking Code Example
PUSH ES
eLI ; Disable interrupts
Set forward pointer to value of interrupt vector in low memory
ASSUME CS:CODESEG,DS:CODESEG
PUSH ES
HOV
AX,350FH
DOS get interrupt vector
IHT 21H
HOV
51,OFFSET CS:FPTR Get offset of your forward pointer
in an indexable register
KOV CS: (SI(,BX store the old interrupt vector
KOV
CS: (SI+2) ,ES in your forward pointer for chaining
CKP
ES:BYTE PTR[BXJ.CFH Test for IRET
JNZ
SETVECTR
KOV
CS:FLAGS,FIRST set up first in chain flag
SETVECTR: POP ES
PUSH DS
; Make interrupt vector in low memory point to your handler
KOV DX,OFFSET BNTRY Make interrupt vector point to your handler
MOV AX,SEG ENTRY If OS not
=
es, get it
MOV DS,AX
and put it in DS
KOV AX,250FH
DOS set interrupt vector
INT 21H
POP DS
Unmask (enable) interrupts for your level
IN AL,IMR Read interrupt mask register
JKP $+2 10 delay
AND
AL,07FH Unmask interrupt level 7
OUT IMR,AL write new interrupt mask
KOV AL,SPC_EOI Issue specific EO! for level
JKP
$+Z
to allow pending level 7 interrupts
OUT OCR,AL (if any) to be serviced
STI Enable interrupts
POP ES
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System Board