z80asm - assembler for the Z80 microprocessor
Z80asm is an assembler for Z80 assembly. If no input files are specified, stdin
is used. If no output file is specified, "a.bin" is used. If
"-" is specified as output file, stdout is used. This makes it
possible to use the assembler in a pipeline.
When multiple input files are specified, the assembler first uses all files
which were specified with -i or --input, in the order given. After that, all
files which were specified as non-option arguments are assembled, also in the
- -h, --help
- Show summary of options and exit.
- -V, --version
- Display version information and exit.
- -v, --verbose
- Be verbose. Specify multiple times to be more verbose. Messages are sent
to standard error.
- -l, --list[=filename]
- Write a list file. No filename or '-' means stderr.
- -L, --label[=filename]
- Write a label file. No filename or '-' means stderr.
- -p, --label-prefix=prefix
- prefix all labels with this prefix.
- -i, --input=filename
- Specify an input file (-i may be omitted). '-' means stdin.
- -o, --output=filename
- Specify the output file. '-' or completely omitting the option means
- -I, --includepath=dirname
- Add a directory to the include path. The order in which the directories
are tried is from back to front: the last directory specified has the
highest priority. "/usr/share/z80asm" is always in the include
path (with lowest priority), you don't have to specify it.
- -f, --force
- Produce output even in case of errors. Normally the output, list and label
files are removed when assembly is unsuccesful.
All mnemonics and registers are case insensitive. All other text (in particular,
labels and macros) are not. Undocumented opcodes are as much as possible
- sll and sli are equal and can both be used.
- ixh, ixl, iyh and iyl can be used.
Assembler directives are:
- incbin 'filename'
- Include a binary file into the resulting assembled file. This can be used
to include text files, or images, sound files, etc. The filename is
searched for in the current directory, and then in the include path, just
like for include. Also like for include, the quotes can be any character
(but must match) and no substitution is performed (so ~ is not your home
- defb or db arg, arg, arg, ...
- Define bytes.
- defm or dm "String", 'String'
- Define message. Each character in the string is stored as one byte.
Backslash escapes are allowed, as in characters in expressions. Unlike the
argument for include, the quotes must really be quotes (but they can be
single or double quotes. The closing quote must match the opening
defb/db and defm/dm are really aliases; either can take both quoted strings and
defb "This text should be in a buffer\r\n", 0
- defs or ds count [, value]
- Define space. count bytes are reserved. Each of them is initialised to the
specified value, or 0 if no value is specified.
- defw or dw arg, arg, arg, ...
- Define words. Each argument is stored as two bytes, the low order byte
- End assembly of this source file. Any remaining lines are copied into the
list file (if present), but not assembled.
- label: equ expression
- Define label to have value expression.
code block 1
code block 2
code block 3
code block n
Conditionally assemble code. If expression is not 0, all
odd code blocks are assembled, if expression is 0, all even blocks are
assembled. Usually only one or two code blocks are present.
- include 'file'
- Include file into the source. The quotes around the file for include are
mandatory, but you can choose the quotes yourself. eg, you may use % or
even a letter as a quote. The filename does not undergo any expansion, so
\, ~, $, etc are passed as written (which means ~ will not be your home
directory.) The filename is used as specified, and then prefixed with each
directory in the include path, until it can be opened.
arg1, arg2, ...
Define a macro. The macro can be used where an opcode is
expected. The code block is then substituted, with the given values for the
arguments. This is a textual substitution, so the following example is
This will generate a label with a constructed name (it's
not a very useful example, but it shows the possiblities).
- org address
- Set the "program counter" to address. This does not add any
bytes to the resulting binary, it only determines how the rest of the code
is interpreted (in particular, the value of labels and $).
- seek offset
- Seek to position offset in the output file. This can be used for
overwiting previously assembled code, for example for patching a binary
which was included using incbin.
All expressions can use the following operators, in order of precedence:
- a ? b : c
- If a is not zero, return b, otherwise c
- a | b
- bitwise or
- a ^ b
- bitwise xor
- a & b
- bitwise and
- a == b, a = b, a != b
- a <= b, a >= b, a < b, a > b
- a << b, a >> b
- bit shift
- a + b, a - b
- addition and subtraction
- a * b, a / b, a % b
- multiplication, division and modulo
- ~a, +a, -a
- bitwise not, no effect and negation
- 1 if label exists, 0 if it does not. This does not generate an error if
label does not exist. Note that this is usually evaluated immediately (if
the rest of the expression permits), and it does not check if the label is
defined later. This means it can be used as the argument of if , to
get the functionality of #ifdef in C.
Literals in expressions may be written as: (case does not matter)
- arbitrary base number (specified by 'c' so c+1 == 10: here base is
- 14, 14d, @914
- decimal number
- 016, 16o, 16q, &o16, @716
- octal number
- 0Eh, 0xE, &hE, $E, @FE
- hexadecimal number (for the first notations, the first character must be
- %1110, 1110b, &b1110, @11110
- binary number
- ASCII code of 's'
- '\n', '\r', '\a', '\t'
- Newline, carriage return, alert, tab
- Octal ASCII code
- address of first byte of current command
In all expressions, labels may be used. However, there are some expressions
where the value must be computable at once, and therefore only previously
defined labels may be used. This is the case for:
- - The argument of org
- - The argument of seek
- - The argument of equ (eg, a label definition)
- - The first argument of ds
- - The argument of if
In all other expressions, labels which are defined later may be used.
Labels must consist of letters, digits, underscores and periods, and must not
start with a digit. Labels are case sensitive.
Labels starting with a period (.) are local
, which means their scope is
only the current include file or macro definition (and files included/macros
called from it). This is particularly useful for macros, to prevent duplicate
definitions when using a macro more than once.
If assembly was successful, no output is produced (except the result, and
messages triggered by --verbose) and 0 is returned. At any error, there is
output on the standard error and 1 is returned.
Parts that are not assembled because of an if statement and macros which are
defined but never used are only checked to have a correct command. The
argument is not parsed. This means that if the file passes through the
assembler with no warnings or errors, it may still not assemble correctly in a
different setting (where the if's give different results).
If you find a bug, or want to send comments, please use the web interface at
http://savannah.nongnu.org/projects/z80asm/ or send an e-mail to
Z80asm was written by Bas Wijnen <firstname.lastname@example.org>. Some patches were
provided by Jan Wilmans <email@example.com>