Specifications

Application Examples
;***********************************************************
;* *
;* INTERRUPT HANDLERS *
;* *
;***********************************************************
;
; ONLY ONE SERIAL INTERRUPT HANDLER IS ILLUSTRATED. OTHER
; HANDLERS CAN BE ADDED HERE AS NEEDED.
;
CODE SEGMENT PARA
;
ASSUME CS:CODE,SS:STACK,DS:DATA,ES:NOTHING
;
LED_STROBE PROC
;
; THIS PROCEDURE HANDLES THE INTERRUPT GENERATED BY THE
; TIMER 2 ON THE ZT 8809A. FIRST THE PRINTER PORT BIT
; THAT CONTROLS THE LED IS READ AND EXTRACTED, THEN
; INVERTED AND OR’D BACK INTO THE BYTE READ. THE
; BYTE IS THEN REWRITTEN TO THE PRINTER PORT.
;
; INPUTS: NONE
; OUTPUTS: NONE
; CALLS: NONE
; DESTROYS: NONE
;
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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