Application Examples
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INTERRUPT HANDLERS
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; ONLY ONE SERIAL INTERRUPT HANDLER IS ILLUSTRATED.
OTHER
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HANDLERS CAN BE ADDED HERE AS NEEDED.
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CODE
SEGMENT
PARA
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ASSUME
CS:CODE,SS:STACK,DS:DATA,ES:NOTHING
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LED_STROBE
PROC
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; THIS PROCEDURE HANDLES THE INTERRUPT GENERATED BY THE
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TIMER 2 ON THE ZT 8809A. FIRST THE PRINTER PORT BIT
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THAT CONTROLS THE LED IS READ AND EXTRACTED, THEN
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INVERTED AND OR’D BACK INTO THE BYTE READ. THE
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BYTE IS THEN REWRITTEN TO THE PRINTER PORT.
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; INPUTS:
NONE
; OUTPUTS:
NONE
; CALLS:
NONE
; DESTROYS:
NONE
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PUSH
AX
; SAVE REGISTERS USED
PUSH
DX
GET
PRTR_CTRL
; READ THE CONTROL BYTE
MOV
AH,AL
; SAVE IT INTO AH
AND
AH,2
; EXTRACT THE BIT
NOT
AH
; INVERT IT
AND
AH,2
; ZERO ALL OTHERS
AND
AL,0FDH
; ZERO THE BIT IN CTRL BYTE
OR
AL,AH
; OR NEW ONE BACK INTO THE AL
PUT
PRTR_CTRL
; REPLACE INTO CONTROL BYTE
MOV
AL,OCW2_8809A
; SEND EOI FOR IR2
PUT
PORT_A_8809A
POP
DX
POP
AX
IRET
LED_STROBE
ENDP
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4-10
