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2. Usage

2.1 Command line option overview

The assembler accepts the following options:

Usage: ca65 [options] file
Short options:
  -D name[=value]       Define a symbol
  -I dir                Set an include directory search path
  -U                    Mark unresolved symbols as import
  -V                    Print the assembler version
  -W n                  Set warning level n
  -g                    Add debug info to object file
  -h                    Help (this text)
  -i                    Ignore case of symbols
  -l                    Create a listing if assembly was ok
  -mm model             Set the memory model
  -o name               Name the output file
  -s                    Enable smart mode
  -t sys                Set the target system
  -v                    Increase verbosity

Long options:
  --auto-import         Mark unresolved symbols as import
  --cpu type            Set cpu type
  --debug-info          Add debug info to object file
  --feature name        Set an emulation feature
  --forget-inc-paths    Forget include search paths
  --help                Help (this text)
  --ignore-case         Ignore case of symbols
  --include-dir dir     Set an include directory search path
  --listing             Create a listing if assembly was ok
  --list-bytes n        Maximum number of bytes per listing line
  --macpack-dir dir     Set a macro package directory
  --memory-model model  Set the memory model
  --pagelength n        Set the page length for the listing
  --smart               Enable smart mode
  --target sys          Set the target system
  --verbose             Increase verbosity
  --version             Print the assembler version

2.2 Command line options in detail

Here is a description of all the command line options:

--cpu type

Set the default for the CPU type. The option takes a parameter, which may be one of

6502, 65SC02, 65C02, 65816, sunplus, sweet16, HuC6280

The sunplus cpu is not available in the freeware version, because the instruction set is "proprietary and confidential".

--feature name

Enable an emulation feature. This is identical as using .FEATURE in the source with two exceptions: Feature names must be lower case, and each feature must be specified by using an extra --feature option, comma separated lists are not allowed.

See the discussion of the .FEATURE command for a list of emulation features.


Forget the builtin include paths. This is most useful when building customized assembler modules, in which case the standard header files should be ignored.

-g, --debug-info

When this option (or the equivalent control command .DEBUGINFO) is used, the assembler will add a section to the object file that contains all symbols (including local ones) together with the symbol values and source file positions. The linker will put these additional symbols into the VICE label file, so even local symbols can be seen in the VICE monitor.

-h, --help

Print the short option summary shown above.

-i, --ignore-case

This option makes the assembler case insensitive on identifiers and labels. This option will override the default, but may itself be overridden by the .CASE control command.

-l, --listing

Generate an assembler listing. The listing file will always have the name of the main input file with the extension replaced by ".lst". This may change in future versions.

--list-bytes n

Set the maximum number of bytes printed in the listing for one line of input. See the .LISTBYTES directive for more information. The value zero can be used to encode an unlimited number of printed bytes.

--macpack-dir dir

This options allows to specify a directory containing macro files that are used instead of the builtin images when a .MACPACK directive is encountered. If --macpack-dir was specified, a .mac extension is added to the package name and the resulting file is loaded from the given directory. This is most useful when debugging the builtin macro packages.

-mm model, --memory-model model

Define the default memory model. Possible model specifiers are near, far and huge.

-o name

The default output name is the name of the input file with the extension replaced by ".o". If you don't like that, you may give another name with the -o option. The output file will be placed in the same directory as the source file, or, if -o is given, the full path in this name is used.

--pagelength n

sets the length of a listing page in lines. See the .PAGELENGTH directive for more information.

-s, --smart-mode

In smart mode (enabled by -s or the .SMART pseudo instruction) the assembler will track usage of the REP and SEP instructions in 65816 mode and update the operand sizes accordingly. If the operand of such an instruction cannot be evaluated by the assembler (for example, because the operand is an imported symbol), a warning is issued.

Beware: Since the assembler cannot trace the execution flow this may lead to false results in some cases. If in doubt, use the .ixx and .axx instructions to tell the assembler about the current settings. Smart mode is off by default.

-t sys, --target sys

Set the target system. This will enable translation of character strings and character constants into the character set of the target platform. The default for the target system is "none", which means that no translation will take place. The assembler supports the same target systems as the compiler, see there for a list.

-v, --verbose

Increase the assembler verbosity. Usually only needed for debugging purposes. You may use this option more than one time for even more verbose output.


This option allows you to define symbols on the command line. Without a value, the symbol is defined with the value zero. When giving a value, you may use the '$' prefix for hexadecimal symbols. Please note that for some operating systems, '$' has a special meaning, so you may have to quote the expression.

-I dir, --include-dir dir

Name a directory which is searched for include files. The option may be used more than once to specify more than one directory to search. The current directory is always searched first before considering any additional directories. See also the section about search paths.

-U, --auto-import

Mark symbols that are not defined in the sources as imported symbols. This should be used with care since it delays error messages about typos and such until the linker is run. The compiler uses the equivalent of this switch ( .AUTOIMPORT) to enable auto imported symbols for the runtime library. However, the compiler is supposed to generate code that runs through the assembler without problems, something which is not always true for assembler programmers.

-V, --version

Print the version number of the assembler. If you send any suggestions or bugfixes, please include the version number.


Set the warning level for the assembler. Using -W2 the assembler will even warn about such things like unused imported symbols. The default warning level is 1, and it would probably be silly to set it to something lower.

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