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https://github.com/a2-4am/4cade.git
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78 lines
2.2 KiB
Plaintext
78 lines
2.2 KiB
Plaintext
;------------------------------------------------------------------------------
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; Has64K
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; Checks whether computer has functioning language card (64K)
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;
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; in: none
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; out: C clear if 64K detected
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; C set if 64K not detected
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; all other flags and registers clobbered
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; ROM in memory (not LC RAM bank)
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;------------------------------------------------------------------------------
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Has64K
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+READ_RAM1_WRITE_RAM1
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lda #$AA ; test #1 for $D0 page
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sta $D000
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eor $D000
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bne @no
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lsr $D000 ; test #2 for $D0 page
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lda #$55
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eor $D000
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bne @no
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clc
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+HIDE_NEXT_BYTE
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@no sec
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+READ_ROM_NO_WRITE
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rts
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;------------------------------------------------------------------------------
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; Has128K
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; Checks whether computer has functioning auxiliary memory (128K)
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;
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; in: none
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; out: C set if 128K detected
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; C clear if 128K not detected
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; all other flags and registers clobbered
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; zp $80-$9F clobbered
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; ROM in memory (not LC RAM bank)
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;
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; adapted from "Prince of Persia" by Jordan Mechner
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; (c) 1989 Broderbund Software
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; https://github.com/jmechner/Prince-of-Persia-Apple-II/blob/master/01%20POP%20Source/Source/BOOT.S#L119
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;------------------------------------------------------------------------------
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Has128K
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+READ_ROM_NO_WRITE
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sta STOREOFF
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lda ROM_MACHINEID
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cmp #6
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bne @no ; earlier than //e -> no 128K
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lda SLOT3STATUS
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bmi @no ; no 80-column card -> no 128K
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ldx #@checklen
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- lda @checker,x
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sta $80,x
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dex
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bpl -
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jmp $80 ; check if auxmem actually works
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@checker
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lda #$EE
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sta WRITEAUXMEM
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sta READAUXMEM
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sta $0C00
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sta $0800
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lda $0C00
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cmp #$EE
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bne @no
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asl $0C00
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asl
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cmp $0C00
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bne @no
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cmp $0800
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bne @yes
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@no clc
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+HIDE_NEXT_BYTE
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@yes sec
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@finish sta WRITEMAINMEM
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sta READMAINMEM
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rts
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@checklen=*-@checker
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