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clrscr for Atari 5200 default conio screen

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Christian Groessler
2014-05-12 03:05:21 +02:00
parent 82544b8678
commit 8cb68071cd
1 changed files with 34 additions and 0 deletions
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libsrc/atari5200/clrscr.s Normal file
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;
; Christian Groessler, May-2014
;
; void clrscr (void);
;
.export _clrscr
.include "atari5200.inc"
.importzp ptr1
SCRSIZE = 480 ; 20x24: size of default conio atari5200 screen
_clrscr:lda SAVMSC ; screen memory
sta ptr1
lda SAVMSC+1
clc
adc #>(SCRSIZE-1)
sta ptr1+1
lda #0 ; screen code of space char
ldy #<(SCRSIZE-1)
ldx #>(SCRSIZE-1)
_clr1: sta (ptr1),y
dey
bne _clr1
sta (ptr1),y
dex
bmi done
dec ptr1+1
dey
jmp _clr1
done: sta COLCRS_5200
sta ROWCRS_5200
rts