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New get_tv function from Stefan Haubenthal

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git-svn-id: svn://svn.cc65.org/cc65/trunk@3230 b7a2c559-68d2-44c3-8de9-860c34a00d81
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cuz 2004-10-08 20:23:15 +00:00
parent 25cf8a3d27
commit dd6ce2fddd
1 changed files with 33 additions and 0 deletions
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33
libsrc/vic20/get_tv.s Normal file
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;
; Stefan Haubenthal, 2004-10-07
; Based on code from Pu-239
;
; unsigned char __fastcall__ get_tv (void);
; /* Return the video mode the machine is using */
;
.export _get_tv
.include "vic20.inc"
;--------------------------------------------------------------------------
; _get_tv
.proc _get_tv
NTSC_LINES = 261
; detect the system
lda #0
tax
@L0: ldy VIC_HLINE
cpy #1
bne @L0 ; wait for line 1
@L1: ldy VIC_HLINE
beq @L2 ; line 0 reached -> NTSC
cpy #NTSC_LINES/2+2
bne @L1
lda #1
@L2: rts ; system detected: 0 for NTSC, 1 for PAL
.endproc