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readme-original.txt
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readme-original.txt
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--------------------------------------------------------------
ASM6 (v1.6)
A 6502 assembler by loopy (loopy at mm.st)
--------------------------------------------------------------
Yes, it's another 6502 assembler. I built it to do NES development, but you
can probably use it for just about anything. Why use this instead of one of
the other zillion assemblers out there? I don't know, but choice is good,
right? :) I wrote it because I thought most others were either too finicky,
had weird syntax, took too much work to set up, or too bug-ridden to be useful.
This is free software. You may use, modify, and / or redistribute any part
of this software in any fashion.
--------------------------------------------------------------
Command line
--------------------------------------------------------------
Usage:
asm6 [-options] sourcefile [outputfile] [listfile]
Options:
-? Show some help
-l Create listing
-L Create verbose listing (expand REPT, MACRO)
-d<name>: Define a symbol and make it equal to 1
-q Quiet mode (suppress all output unless there's an error)
Default output is <sourcefile>.bin
Default listing is <sourcefile>.lst
--------------------------------------------------------------
Syntax
--------------------------------------------------------------
Comments begin with a semicolon (;). A colon (:) following a label is
optional.
examples:
lda #$00 ;hi there
label1: jmp label2
label2 beq label1
--------------------------------------------------------------
Numbers and expressions
--------------------------------------------------------------
Hexadecimal numbers begin with '$' or end with 'h'. Binary numbers begin
with '%' or end with 'b'. Characters and strings are surrounded by
single or double quotes. The characters (' " \) within quotes must be
preceded by a backslash (\).
examples:
12345
'12345'
$ABCD
0ABCDh
%01010101
01010101b
Supported operators (listed by precedence):
( )
(unary) + - ~ ! < >
* / %
+ -
<< >>
< > <= >=
= == != <>
&
^
|
&&
||
'=' and '<>' are equivalent to C's '==' and '!=' operators. The unary '<'
and '>' operators give the lower and upper byte of a 16-bit word (respectively).
All other operators function like their C equivalents.
--------------------------------------------------------------
Labels
--------------------------------------------------------------
Labels are case sensitive. The special '$' label holds the current program
address. Labels beginning with '@' are local labels. They have limited scope,
visible only between non-local labels. Names of local labels may be reused.
label1:
@tmp1:
@tmp2:
label2:
@tmp1:
@tmp2:
Labels beginning with one or more '+' or '-' characters are nameless labels,
especially useful for forward and reverse branches.
example:
-- ldx #0
- lda $2002 ;loop (wait for vblank)
bne -
- lda $2002 ;nameless labels are easy to reuse..
bne -
cpx #69
beq + ;forward branch..
cpx #96
beq +here ;use more characters to make more unique
jmp -- ;multiple --'s handy for nested loops
+ ldx #0
+here nop
--------------------------------------------------------------
Assembler directives (in no particular order)
--------------------------------------------------------------
All directives are case insensitive and can also be preceded by a period (.)
EQU
For literal string replacement, similar to #define in C.
one EQU 1
plus EQU +
DB one plus one ;DB 1 + 1
=
Unlike EQU, statements with '=' are evaluated to a number first.
Also unlike EQU, symbols created with '=' can be reused.
i=1
j EQU i+1
k=i+1 ;k=1+1
i=j+1 ;i=i+1+1
i=k+1 ;i=2+1
INCLUDE (also INCSRC)
Assemble another source file as if it were part of the current
source.
INCLUDE whatever.asm
INCBIN (also BIN)
Add the contents of a file to the assembly output.
moredata: INCBIN whatever.bin
An optional file offset and size can be specified.
INCBIN foo.bin, $400 ;read foo.bin from $400 to EOF
INCBIN foo.bin, $200, $2000 ;read $2000 bytes, starting from $200
DB, DW (also BYTE/WORD, DCB/DCW, DC.B/DC.W)
Emit byte(s) or word(s). Multiple arguments are separated by
commas. Strings can be "shifted" by adding a value to them (see
example).
DB $01,$02,$04,$08
DB "ABCDE"+1 ;equivalent to DB "BCDEF"
DB "ABCDE"-"A"+32 ;equivalent to DB 32,33,34,35,36
DL, DH
Similar to DB, outputting only the LSB or MSB of a value.
DL a,b,c,d ;equivalent to DB <a, <b, <c, <d
DH a,b,c,d ;equivalent to DB >a, >b, >c, >d
HEX
Compact way of laying out a table of hex values. Only raw hex values
are allowed, no expressions. Spaces can be used to separate numbers.
HEX 456789ABCDEF ;equivalent to DB $45,$67,$89,$AB,$CD,$EF
HEX 0 1 23 4567 ;equivalent to DB $00,$01,$23,$45,$67
DSB, DSW (also DS.B/DS.W)
Define storage (bytes or words). The size argument may be followed
by a fill value (default filler is 0).
DSB 4 ;equivalent to DB 0,0,0,0
DSB 8,1 ;equivalent to DB 1,1,1,1,1,1,1,1
DSW 4,$ABCD ;equivalent to DW $ABCD,$ABCD,$ABCD,$ABCD
PAD
Fill memory from the current address to a specified address. A fill
value may also be specified.
PAD $FFFA ;equivalent to DSB $FFFA-$
PAD $FFFA,$EA ;equivalent to DSB $FFFA-$,$EA
ORG
Set the starting address if it hasn't been assigned yet, otherwise
ORG functions like PAD.
ORG $E000 ;start assembling at $E000
.
.
.
ORG $FFFA,$80 ;equivalent to PAD $FFFA,$80
ALIGN
Fill memory from the current address to an N byte boundary. A fill
value may also be specified.
ALIGN 256,$EA
FILLVALUE
Change the default filler for PAD, ALIGN, etc.
FILLVALUE $FF
BASE
Set the program address. This is useful for relocatable code,
multiple code banks, etc. The same can also be accomplished by
assigning the '$' symbol directly (i.e. '$=9999').
oldaddr=$
BASE $6000
stuff:
.
.
.
BASE oldaddr+$-stuff
IF / ELSEIF / ELSE / ENDIF
Process a block of code if an expression is true (nonzero).
IF j>0
DB i/j
ELSE
DB 0
ENDIF
IFDEF / IFNDEF
Process a block of code if a symbol has been defined / not defined.
IFDEF _DEBUG_
.
.
.
ENDIF
MACRO / ENDM
MACRO name args...
Define a macro. Macro arguments are comma separated.
Labels defined inside macros are local (visible only to that macro).
MACRO setAXY x,y,z
LDA #x
LDX #y
LDY #z
ENDM
setAXY $12,$34,$56
;expands to LDA #$12
; LDX #$34
; LDY #$56
REPT / ENDR
Repeat a block of code a specified number of times.
Labels defined inside REPT are local.
i=0
REPT 256
DB i
i=i+1
ENDR
ENUM / ENDE
Reassign PC and suppress assembly output. Useful for defining
variables in RAM.
ENUM $200
foo: db 0
foo2: db 0
ENDE
ERROR
Stop assembly and display a message.
IF x>100
ERROR "X is out of range :("
ENDIF
--------------------------------------------------------------
<EOF>