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; seek.asm - seek example
; Copyright 2005 jancasper
;
; This file is part of z80asm.
;
; Z80asm is free software; you can redistribute it and/or modify
; it under the terms of the GNU General Public License as published by
; the Free Software Foundation; either version 3 of the License, or
; (at your option) any later version.
;
; Z80asm is distributed in the hope that it will be useful,
; but WITHOUT ANY WARRANTY; without even the implied warranty of
; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
; GNU General Public License for more details.
;
; You should have received a copy of the GNU General Public License
; along with this program. If not, see <http://www.gnu.org/licenses/>.
; this org not strictly necessary
org $4000
; load an existing rom, 16384 bytes in size, which was originally assembled at $4000
incbin 'disk.rom'
; seek back to absolute position 16 in the output file
seek $10
; since the rom is loaded at addres $4000, code at $10 should be referred to as $4010
org $4010
; the following instructions will overwrite the code at $10
jp diskio
jp dskchg
jp getdpb
jp choice
jp dskfmt
jp drvoff
seek $3410
org $7410
diskio:
dskchg:
getdpb:
choice:
dskfmt:
drvoff:
add a,2
add 2
sub a,2
sub 2
ei
ret
; The result of this will be a new, patched binary rom file that is still exactly 16384 bytes in size.
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