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e444f4c40e
Check the Pascal ID bytes for an 80-columns card to avoid blindly jumping into a $C300 that could be totally unrelated.
53 lines
1.2 KiB
ArmAsm
53 lines
1.2 KiB
ArmAsm
;
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; Oliver Schmidt, 07.09.2009
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;
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; signed char __fastcall__ videomode (unsigned mode);
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;
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.export _videomode
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.import aux80col
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.import returnFFFF
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.include "apple2.inc"
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VIDEOMODE_40x24 = $15
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VIDEOMODE_80x24 = $00
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.segment "LOWCODE"
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_videomode:
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bit aux80col
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bmi set_mode
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; No 80 column card, return error if requested mode is 80cols
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cmp #VIDEOMODE_40x24
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beq out
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jmp returnFFFF
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set_mode:
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; Get and save current videomode flag
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bit RD80VID
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php
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; Initializing the 80 column firmware needs the ROM switched
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; in, otherwise it would copy the F8 ROM to the LC (@ $CEF4)
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bit $C082
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; Call 80 column firmware with ctrl-char code
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jsr $C300
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; Switch in LC bank 2 for R/O
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bit $C080
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; Switch in alternate charset again
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sta SETALTCHAR
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; Return ctrl-char code for setting previous
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; videomode using the saved videomode flag
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lda #VIDEOMODE_40x24
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plp
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bpl out
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lda #VIDEOMODE_80x24
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out: rts ; X was preserved all the way
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