xkas (acronym for: cross-knight assembler) is a cross-assembler for the WDC G65816 processor, specifically tailored for use with SFC/SNES programming and translations but also supports GBA Thumb CPU (ARM7TDMI Thumb). The documentation below is for the most recent version of xkas.


  • Supports All 256 Opcodes
  • Supports Labels / Sublabels / +/- Labels
  • Supports Math
  • Supports ASCII-Tables
  • Supports Defines
  • Supports Macros


  • xkas v0.06
  • xkas v0.06 Unoffical
  • xkas v0.08 Unoffical
  • xkas v0.12
  • xkas v0.14

Command Line

xkas -o output.bin input.asm [second-input.asm ...]

If the output file exists, xkas will assemble the source file on top of this file. If it does not exist, xkas will create the file. Usage examples:

xkas -o output.bin input.asm
xkas -o output.bin input1.asm input2.asm
xkas input1.asm input2.asm -o output.bin


arch type

Select processor architecture. Supported values:

none      - None; uses base commands only
snes.cpu  - SNES CPU (WDC 65816)

endian type

Manually specify processor endian. This will affect dw, dl and dd commands. Note that selecting a processor architecture will automatically select endian. This is intended to be used for "arch none" only. Supported values:

lsb - Little endian
msb - Big endian

incsrc filename.asm

Include additional source file. Note that this command is infinitely recursive. Eg file1.asm can incsrc file2.asm, which can incsrc file3.asm. Recursion is only limited to available memory. The state will remain unchanged, eg all defines and labels will remain in-tact.

incbin filename.bin

Insert binary file directly into output.

org offset

Seek to specified offset. Offset address relativity to output file is based upon the current architecture. Eg if arch = snes.cpu, org should be an SNES-memory-mapped offset. For arch = none, this is a literal offset into the output file.

base offset

Override internal org address when computing eg labels. This is useful for relocatable code and custom address mapping. Usage example:

org $c02000; base $7f0000
lda #$00
  jml loop //will assemble as jml $7f0002; while writing to pc($c02002) 

align modulus

Write 0x00s until offset is evenly divisible by modulus. Eg if offset is $8011, "align 4" will write three 0x00s, aligning offset to a 4-byte boundary; in this case, $8014.

db / dw / dl / dd value [, value, "string", ...]

Simple binary data insertion; these are used to write binary data to the file. These commands additionally support quote-delimited 7-bit ANSI encoded strings.

db - Data byte (8-bits)
dw - Data word (16-bits)
dl - Data long (24-bits)
dd - Data double word (32-bits)

fill length [, value]

Writes "length" number of bytes to output file. If value is not specified, write value is 0x00.

fillto offset [, value]

Writes until "offset" is reached. If value is not specified, write value is 0x00.

define name "value"

Creates a new define, or overrides a previous define by the same name. Quotes are only needed if space is needed inside the define. Usage example:

define add "clc; adc"
define health_bonus 32
{add}.w #{health_bonus} //will assemble as clc; adc.w #32 

define 'char' value

Redefine string table entry. "char" must be exactly one ANSI character in length, and "value" must resolve to an integer. Usage example:

define 'C' $1234 // value can be up to 64-bits in length
lda.b #'C'       // will assemble as lda.b #$34
lda.w #'C'       // will assemble as lda.w #$1234
dw "C"           // will write #$1234 to output


Creates a new label. A label is used to represent a position in code, and allows one to code without having to constantly update branches and jumps/calls. A label should be able to be used in any opcode, but was specifically added to be used with branches, jumps, and calls. Can start with _[A-Za-z], can contain _[A-Za-z0-9].


Creates a new sublabel. A sublabel is used to declare labels within labels that will share its address space only, and can contain the same characters as a label. Must start with ., can contain _[A-Za-z0-9]. Sublabel is automatically prefixed with the most recently specified label. Example:

.sublabel: // will assemble as label.sublabel 

+ / - label:

Creates a nameless label. Will ignore active namespace. + is used to point to a label after the current code position, - is used to point before the current position. Can be redefined at any point in the code. Example:

-; dex; beq +; ...; bra -
+; rts

namespace name

Sets the active namespace. When a label, sublabel or define is specified without a namespace prefix, it is automatically prefixed by the active namespace. This defaults to "global". Note that unlike C++ namespaces, this function is not recursive. There is only one namespace level. Example:

namespace global
define def "0"
dw label, .sublabel, custom::label, custom::label.sublabel, {def}, {custom::def}

namespace custom
define def "1"
dw label, .sublabel, global::label, global::label.sublabel, {def}, {global::def} 

print arg [, arg, "string", ...]

Prints specified message to the terminal. Example:

org $8000
print "label1 offset = ", org //prints "label1 offset = 0x8000"

Written by byuu August 1st, 2004 - October 19th, 2010