Listing of file='LPTEST.MAC;01' on disk='vmedia/sound_light_pen-sector.ccvf'
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;
; LIGHT-PEN TEST ROUTINE
;
; VALUES ON ENTRY ARE IRRELEVANT
;
; RETURNS:
; DE = 0 MEANS NO LIGHT
; DE = -1 MEANS LIGHT PRESENT
; NOTE: DE IS USED FOR COMPATIBILITY WITH BASIC
;
; DESTROYS:
; ACC, AND OF COURSE DE
;
ENTRY LPTEST
LPTEST: MVI D,10
TS10: MVI E,0FFH
TS20: MVI A,14 ;SELECT PORT 'A' ON AY-3-8910
OUT 30H
IN 30H ;READ IT
ANI 01 ;TEST PEN FOR LIGHT PRESENT
JNZ TS25 ;NO, LOOP
NOP ;WAIT A LITTLE
NOP
MVI A,14 ;CHECK PEN AGAIN ('DEBOUNCE')
OUT 30H
IN 30H
ANI 01
JZ TS30
TS25: DCR E
JNZ TS20
DCR D
JNZ TS10
RET ;RETURN ZERO FOR NOT LIT
TS30: MVI D,0FFH
MOV E,D
RET ;RETURN -1 FOR LIT
END