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<html>
<head>
<title>CASM - A simple, portable multi-pass assembler</title>
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<body>
<div class="legalise">
<p><b>casm</b> is a simple, portable multi-pass assembler</p>
<p>Copyright (C) 2003-2015 Ian Cowburn</p>
<p>This program 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.</p>
<p>This program 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.</p>
<p>You should have received a copy of the GNU General Public License
along with this program. If not, see
<a href="http://www.gnu.org/licenses/gpl-3.0.html">
http://www.gnu.org/licenses/gpl-3.0.html)</a></p>
</div>
<h1>Index</h1>
<p>
<a href="#casm">CASM</a> - General usage
</p>
<p>
<a href="#z80">Z80</a> - Z80 processor support.
</p>
<p>
<a href="#6502">6502</a> - 6502 processor support.
</p>
<p>
<a href="#gbcpu">Gameboy Z80</a> - The Gameboy Z80 derivative processor.
</p>
<h1 id="casm">CASM</h1>
<h2>Usage</h2>
<div class="codeblock">
casm <i>file</i>
</div>
<p>Assembles <i>file</i>, and places the resulting code in a file called
<b>output</b> by default.</p>
<p>Note that switches aren't used by <b>casm</b>. Instead options are
controlled by commands in the source <i>file</i>.</p>
<p>If you type the command without an argument, usage, version and license
info is displayed.</p>
<h2>Memory Layout</h2>
<p>There is 64K of RAM that the assembler will generate output into. Extra 64K
banks of RAM can be added by using the <b>bank</b> or <b>org</b> directives.
Banks are numbered from zero upwards.</p>
<h2>Source Code Layout</h2>
The source files follow this basic format:
<pre class="codeblock">
; Comments
;
label1: equ 0xffff
org $4000;
db "Hello, World\n",0
main jp local_label ; Comments
.local_label
inc a
another:
inc b
jp local_label ; Actually jumps to the following
; local_label.
.local_label
ret
</pre>
<p>The source files follow the following rules:</p>
<ul>
<li>Any text past a semicolon (;) is discarded as a comment (except when part
of a string constant).</li>
<li>Labels must start in column zero (the left hand most column).</li>
<ul>
<li>If the label ends with a colon (:) then the colon is removed.</li>
<li>If the label doesn't start with a period (.) then it is assumed a global
label.</li>
<li>If the label starts with a period (.) then it is assumed to be a local
label. Local labels are associated with the preceding global label.
If a global label and related local label have the same name, the local
label will be used on expansion.</li>
<li>Any label can be followed by an <code>equ</code> directive, in which case
the label is set to that value rather than the current program counter.</li>
<li>Labels are case-insensitive.</li>
</ul>
<li>Directives and opcodes must appear further along the line (anywhere else
other than the left hand column where labels live basically).</li>
<li>Strings can either be quoted with single or double quotes; this allows you
to put the other quote type inside the string.</li>
</ul>
<h2>Recognised directives</h2>
<p>The following directives are also recognised with an optional period (.) in
front of them, and are case insensitive. Directives can also be used to
control the output of a program listing, and the output of the assembly
itself. These are documented in subsequent sections.</p>
<table>
<thead><tr><td class="head">Directive</td>
<td class="head">Description</td></tr></thead>
<tr>
<td class="cmd">
processor <i>cpu</i>
</td>
<td class="def">
Sets the processor type to <i>CPU</i>. If omitted then Z80 is the default.
Note that this can appear multiple times in the same file. See the later
sections on processors to see what values are supported.</p>
</td></tr>
<tr><td class="cmd">
option <i>setting</i>, <i>value</i>
</td>
<td class="def">
Set options. Options are defined later on, and each CPU and output driver
can also have its own options. For options that support booleans
(on/off/true/false),the <i>setting</i> can be prefixed with a plus or minus
character to switch it on or off respectively.
</td></tr>
<tr><td class="cmd">
equ <i>value</i></code>
</td>
<td class="def">
Sets the top level label to <i>value</i>. Note this requires a label on the
same line as this directive.
</td></tr>
<tr><td class="cmd">
org <i>value</i>[, <i>bank</i>]
</td>
<td class="def">
Sets the program counter (PC) to <i>value</i>. The PC defaults to zero on
initialisation. If the optional second argument is passed the current memory
bank in use is set to <i>bank</i>. Note that it also possible to set the
bank by passing a 24-bit address. This was added for convenience when using the
65c618 processor.
</td></tr>
<tr><td class="cmd">
bank <i>value</i>
</td>
<td class="def">
The current memory bank in use is set to <i>value</i>.
</td></tr>
<tr><td class="cmd">
ds <i>value</i>[, <i>fill</i>]
</td>
<td class="def">
Skips the program counter on <i>value</i> bytes. If the optional <i>fill</i> is
provided then the bytes are filled with <i>fill</i>, otherwise they are filled
with zero.
</td>
<tr><td class="cmd">
db <i>value</i>[, <i>value</i>]
</td>
<td class="def">
Writes bytes represented by <i>value</i> to the current PC. The values can be
constants, expressions, labels or strings which are expanded to a list of byte
values for each character in the string.
</td></tr>
<tr><td class="cmd">
dw <i>value</i>[, <i>value</i>]
</td>
<td class="def">
Writes words (16-bit values) represented by <i>value</i> to the current PC.
The values can be constants, expressions, labels or strings. Strings are
written as 16-bit versions of their byte values, i.e. the high byte will be zero
and the low byte the character code.
</td></tr>
<tr><td class="cmd">
align <i>value</i>[, <i>fill</i>]
</td>
<td class="def">
Align the PC so that (PC modulus <i>value</i>) is zero. Will error if
<i>value</i> is less than 2 or greater that 32768. No values are written to
the skipped bytes unless the optional <i>fill</i> is supplied.
</td></tr>
<tr><td class="cmd">
include <i>filename</i></code>
</td>
<td class="def">
Includes the source file <i>filename</i> as if it was text entered at the
current location.
</td></tr>
<tr><td class="cmd">
incbin <i>filename</i>
</td>
<td class="def">
Includes the binary file <i>filename</i> at the current PC, as if it was a
sequence of <code>db</code> directives with all the bytes from the file.
</td></tr>
<tr><td class="cmd">
alias <i>command</i>, <i>replacement</i>
</td>
<td class="def">
Creates an alias so that whenever the command <i>command</i> is found in the
source it is replaced with <i>replacement</i>. The idea of this is to make it
easier to import sources that use unknown directives, e.g.
<pre class="codeblock">
alias setaddr,org
alias ldreg,ld
cpu z80
setaddr $8000 ; These two are
org $8000 ; equivalent.
ld a,(hl) ; These two are
ldreg a,(hl) ; equivalent.
</pre>
</td></tr>
<tr><td class="cmd">
nullcmd
</td>
<td class="def">
Simply does nothing. It's only real use is as an alias if you wished to
strip a directive from a foreign source file.
</td></tr>
<tr><td class="cmd">
end
</td>
<td class="def">
Terminates input processing. Anything past the directive will be ignored.
</td></tr>
</table>
<h3>Built-in Aliases</h3>
The following are built-in aliases for the above directives.
<table>
<thead><tr><td class="head">Command</td>
<td class="head">Built-in Alias</td></tr></thead>
<tr><td class="cmd">processor</td>
<td class="alias">
proc<br>
arch<br>
cpu<br>
</td></tr>
<tr><td class="cmd">equ</td>
<td class="alias">
eq
</td></tr>
<tr><td class="cmd">ds</td>
<td class="alias">
defs
</td></tr>
<tr><td class="cmd">db</td>
<td class="alias">
defb<br>
byte<br>
text<br>
</td></tr>
<tr><td class="cmd">dw</td>
<td class="alias">
defw<br>
word<br>
</td></tr>
</table>
<h2>Expressions</h2>
<p>In any of the directives above, where a value is defined, an expression can
be entered.</p>
<p>Assembly instructions will also permit these expressions to be used where
applicable. As many opcodes use parenthesis to indicate addressing modes,
remember that {} brackets can be used to alter expression precedence.</p>
<pre class="codeblock">
ld a,{8+2}*2 ; On the Z80 loads A with the value 20
ld a,({8+2}*2) ; On the Z80 loads A with the value stored at
; address 20
</pre>
<p>Note that the expression is evaluated using a standard C int, and then cast
to the appropriate size.</p>
<p>The following formats for constant numbers are supported:</p>
<table>
<thead><tr><td class="head">Format (regular expression)</td>
<td class="head">Description</td></tr></thead>
<tr><td class="cmd">
"." <i>or</i> '.'
</td>
<td class="def">
A single quoted character will be converted into the appropriate character
code.
</td></tr>
<tr><td class="cmd">
[1-9][0-9]*
</td>
<td class="def">
A decimal number, e.g. 42.
</td></tr>
<tr><td class="cmd">
0[0-7]*
</td>
<td class="def">
An octal number, e.g. 052.
</td></tr>
<tr><td class="cmd">
0x[0-9a-fA-f]+
</td>
<td class="def">
A hex number, e.g. 0x2a.
</td></tr>
<tr><td class="cmd">
[0-9a-fA-f]+h
</td>
<td class="def">
A hex number, e.g. 2ah.
</td></tr>
<tr><td class="cmd">
$[0-9a-fA-f]+
</td>
<td class="def">
A hex number, e.g. $2a.
</td></tr>
<tr><td class="cmd">
[01]+b
</td>
<td class="def">
A binary number, e.g. 00101010b
</td></tr>
<tr><td class="cmd">
%[01]+
</td>
<td class="def">
A binary number, e.g. %00101010
</td></tr>
<tr><td class="cmd">
[a-zA-Z_0-9]+
</td>
<td class="def">
A label, e.g. `main_loop`.
</td></tr>
</table>
The following operators are understood. The order here is the order of
precedence.
<table>
<thead><tr><td class="head">Arithmetic Operators</td>
<td class="head">Description</td></tr></thead>
<tr><td class="cmd">
{ }
</td>
<td class="def">
Brackets used to alter the order of precedence. Note normal parenthesis
aren't used as the assembly language may make use of them.
</td></tr>
<tr><td class="cmd">
~ + -
</td>
<td class="def">
Bitwise NOT/unary plus/unary minus.
</td></tr>
<tr><td class="cmd">
<< >>
</td>
<td class="def">
Shift left/shift right.
</td></tr>
<tr><td class="cmd">
/ *
</td>
<td class="def">
Division/multiplication
</td></tr>
<tr><td class="cmd">
+ -
</td>
<td class="def">
Addition/subtraction.
</td></tr>
</table>
All the following have the same precedence, and so will be done left to right.
<table>
<thead><tr><td class="head">Comparison Operators</td>
<td class="head">Description</td></tr></thead>
<tr><td class="cmd">
==
</td>
<td class="def">
Equality. Returns 1 if the arguments are equal, otherwise zero.
</td></tr>
<tr><td class="cmd">
!=
</td>
<td class="def">
Inequality. Returns 1 if the arguments are unequal, otherwise zero.
</td></tr>
<tr><td class="cmd">
< <= > >=
</td>
<td class="def">
Less than/less than or equal/greater than/greater than or equal. Returns 1
if the arguments are equal, otherwise zero.
</td></tr>
</table>
All the following have the same precedence, and so will be done left to right.
<table>
<thead><tr><td class="head">Boolean Operators</td>
<td class="head">Description</td></tr></thead>
<tr><td class="cmd">
&& &
</td>
<td class="def">
Boolean/bitwise AND. For boolean operation arguments, zero is FALSE,
otherwise TRUE.
</td></tr>
<tr><td class="cmd">
|| |
</td>
<td class="def">
Boolean/bitwise OR.
</td></tr>
<tr><td class="cmd">
^
</td>
<td class="def">
Bitwise XOR.
</td></tr>
</table>
<h2>Character Sets</h2>
<p>The assembler has built-in support for a few different character sets.
These can be set by using the options `charset` or `codepage`, i.e.</p>
<pre class="codeblock">
option codepage, <i>format</i>
option charset, <i>format</i>
</pre>
<p>The following values can be used for <i>format</i>.</p>
<table>
<thead><tr><td class="head">Format</td>
<td class="head">Description</td></tr></thead>
<tr><td class="cmd">
ascii
</td>
<td class="def">
7-bit ASCII. This is the default.
</td></tr>
<tr><td class="cmd">
spectrum
</td>
<td class="def">
The character codes as used on the Sinclair ZX Spectrum.
</td></tr>
<tr><td class="cmd">
cbm
</td>
<td class="def">
PETSCII as used on the Commodore Business Machine's range from the
PET to the C128. See <a href="https://en.wikipedia.org/wiki/PETSCII">
https://en.wikipedia.org/wiki/PETSCII</a> more details.
</td></tr>
<tr><td class="cmd">
zx81
</td>
<td class="def">
The character codes as used on the Sinclair ZX81. Lower case
letters are encoded as normal upper case letters and upper case
letter will be encoded as inverse upper case letters. In addition the following
characters that have no corresponding ZX81 character are mapped as:
<table>
<tr><td class="cmd">
#
</td>
<td class="def">
The British Pound sign.
</td></tr>
<tr><td class="cmd">
'
</td>
<td class="def">
Inverse double quotes.
</td></tr>
<tr><td class="cmd">
\
</td>
<td class="def">
Inverse slash.
</td></tr>
<tr><td class="cmd">
!
</td>
<td class="def">
Inverse question mark.
</td></tr>
<tr><td class="cmd">
|
</td>
<td class="def">
Inverse space.
</td></tr>
<tr><td class="cmd">
~
</td>
<td class="def">
Inverse minus sign.
</td></tr>
<tr><td class="cmd">
{ }
</td>
<td class="def">
Inverse round brackets.
</td></tr>
<tr><td class="cmd">
`
</td>
<td class="def">
The newline character. Note that the newline is actually a HALT opcode used to
terminate the line.
</td></tr>
</table>
</td></tr>
</table>
<p>e.g.</p>
<pre class="codeblock">
option +list
option +list-hex
option charset,ascii
db "Hello",'A'
; $48 $65 $6C $6C $6F $41
option charset,zx81
db "Hello",'A'
; $AD $2A $31 $31 $34 $A6
option codepage,cbm
db "Hello",'A'
; $48 $45 $4C $4C $4F $41
option codepage,spectrum
db "Hello",'A'
; $48 $65 $6C $6C $6F $41
</pre>
<h2>Macros</h2>
<p>
Macros can be defined in one of two ways; either parameterless or with named
parameters. Macro names are case-insensitive. In the parameterless mode the
special identifier '*' can be used to expand all arguments, which will be
separated with commas.
</p>
<p>
When expanded the macro will have an internally generated top-level label
assigned to it, so local variables will work inside the macro.
</p>
<p>e.g.</p>
<pre class="codeblock">
macro1: macro
ld a,\1
ld b,\2
ld hl,data
call \3
jr dataend
.data
defb \*
.dataend
endm
macro2: macro char,junk,interface
ld a,@char
ld b,@junk
call @interface
endm
</pre>
<p>
Note that trying to expand and unknown/missing argument will be replaced with
an empty string. Also the two argument reference styles can be mixed, though
obviously the @ form only makes sense in a parameterised macro, e.g.
</p>
<pre class="codeblock">
mac: macro char,junk,interface
ld a,@char
ld b,\2
call @interface
endm
</pre>
<p>
The at symbol (@) used for parameter expansion in named argument macros can
be replaced by using the following option, e.g.
</p>
<pre class="codeblock">
option macro-arg-char,&
</pre>
<p>
Note that this is enforced when the macro is <u>used</u> not when it is
defined.
Also the character must not be quoted, as that will be parsed as a string
holding the character code of the character.
</p>
<h2>Output Format</h2>
By default the assembled code is written to a file called <b>output</b> as raw
binary. The generated output can be controlled with the following options.
<table>
<thead><tr><td class="head">Output Option</td>
<td class="head">Description</td></tr></thead>
<tr><td class="cmd">
option output-file, <i>file</i>
</td>
<td class="def">
Send the output to <i>file</i>. Defaults to <b>output</b>.
</td></tr>
<tr><td class="cmd">
option output-bank, <i>printf formatted filename</i>
</td>
<td class="def">
Send the output if multiple banks to use to <i>printf formatted filename</i>.
It defaults to <b>output.%u</b> and accepts just one argument in the
formatting string of an unsigned integer.
If more or a different format specifier is used the behaviour of the assembler
will be undefined. How this is used depends on the output driver.
</td></tr>
<tr><td class="cmd">
option output-type, <i>format</i>
</td>
<td class="def">
Controls the format of the output file. The following are the
supported output formats:
<table>
<tr><td class="cmd">
<a href="#rawout">raw</a>
</td>
<td class="def">
A raw binary image.
</td></tr>
<tr><td class="cmd">
<a href="#specout">spectrum</a>
</td>
<td class="def">
A Spectrum emulator TAP file.
</td></tr>
<tr><td class="cmd">
<a href="#zx81out">zx81</a>
</td>
<td class="def">
A ZX81 emulator P file.
</td></tr>
<tr><td class="cmd">
<a href="#t64out">t64</a>
</td>
<td class="def">
A Commodore 64 T64 tape file.
</td></tr>
<tr><td class="cmd">
<a href="#gameboyout">gameboy</a>
</td>
<td class="def">
A Nintendo Gameboy ROM file.
</td></tr>
</table>
</td></tr>
</table>
The output formats are described in detail in the following sections.
<h3 id="rawout">RAW Output Format</h3>
In this mode the file is created covering the block of memory that the assembly
touched. If memory banks have been used then the <b>output-bank</b> setting is
used to generate the output filename.
<h3 id="specout">Spectrum TAP Output Format</h3>
<p>
Generates a Spectrum TAP file for an emulator. A TAP file is a simple binary
file holding the bytes that the real Spectrum would have written to a tape.
</p>
<p>The TAP file will be given the same name as the output filename, and the
internal code block will also be given the same name, unless memory banks
have been used, in which case each code file in the TAP file will use the
<b>output-bank</b> setting to generate the filename for each block.
</p>
<p>
Remember that TAP files can be concatenated, so the output could be appended to
another TAP file containing a BASIC loader, for example.
</p>
<h3 id="zx81out">ZX81 .P Output Format</h3>
<p>
Generates a P-file for an emulator. A ZX81 .P file is simply a dump of memory
from the system variables onwards.
</p>
<p>This format does not support memory blocks (the .P file is not a container
format) and so will only output anything in the first bank used, and using the
<b>output-file</b> for the filename.
</p>
<p>The output file will be created as a BASIC program, containing a REM
statement holding the machine code, and a command to execute the code. As
such the output will fail if the code in Bank 0 does not start at address 16514.
Your code must also support being executed from this address.
</p>
<p>Another important thing to note is about the display file. In the ZX81
memory map the DFILE can move around depending on the size of the program.
The output driver will create a display file for you. The easiest way to
reference this is to read the DFILE system variable when your program starts.
</p>
<p>Alternatively you can just as easily set up your own display file once
your program starts if you have special requirements, e.g. a display file for
pseudo hi-res.
</p>
<h4>ZX81 .P Output Format options</h4>
<p>The ZX81 output driver supports the following settings that can be set via
an <b>option</b> command.
</p>
<table>
<thead><tr><td class="head">Option</td>
<td class="head">Description</td></tr></thead>
<tr><td class="cmd">
option zx81-margin, <pal|ntsc>
</td>
<td class="def">
Sets the MARGIN system variable appropriately either for the PAL or NTSC
TV system. Defaults to PAL.
</td></tr>
<tr><td class="cmd">
option zx81-autorun, <on|off>
</td>
<td class="def">
Whether the ZX81 should auto run the machine code. Defaults to on.
</td></tr>
<tr><td class="cmd">
option zx81-collapse-dfile, <on|off>
</td>
<td class="def">
Whether the display file should be generated collapsed (e.g. for 1K mode).
Defaults to off.
</td></tr>
</table>
<h3 id="t64out">C64 T64 Tape Output Format</h3>
<p>
Generates a T64 tape file for an emulator.
</p>
<p>The tape file will be given the same name as the output filename, and the
internal code block will also be given the same name, unless memory banks
have been used, in which case then each entry in the tape file will use the
<b>output-bank</b> setting to generate the filename for each entry.
</p>
<p>The first (or only) bank will have a small BASIC program inserted as part of
the generated file. For this reason the first bank should start near the BASIC
area (0x820 should be a safe place to start) unless you have a great
desire for a tape full of zero bytes. This BASIC will simply hold a SYS command
to start the machine code, e.g.
</p>
<pre class="codeblock">
10 SYS 2080
</pre>
<p>Any remaining blocks will be stored as-is without any basic loader.</p>
<h3 id="gameboyout">Nintendo Gameboy ROM File Output Format</h3>
<p>
Generates a ROM file for a Gameboy emulator or hardware. Note that large ROM
sizes have not been extensively checked and verified.
</p>
<p>If a single bank was used during the assembly then a simple 32K ROM is
assumed, and an error will be shown if the addresses used fall outside the range
0x150 to 0x7fff. </p>
<p>Similarly if multiple banks are used then it is assumed that the first bank
is only used in the range 0x150 to 0x3fff, and subsequent banks in the range
0x4000 to 0x7fff. This is to fit in with the method the Gameboy uses to page
memory banks into the upper 16K portion of the normal 32K ROM address space.
</p>
<p>By default the output driver will try and fill in the ROM size and type in
the header properly, but these can be overridden using settings.</p>
<h4>Gameboy ROM Output Format options</h4>
<p>The Gameboy output driver supports the following settings that can be set via
an <b>option</b> command.
</p>
<table>
<thead><tr><td class="head">Option</td>
<td class="head">Description</td></tr></thead>
<tr><td class="cmd">
option gameboy-colour, <on|off>
</td>
<td class="def">
Whether this is a Gameboy Colour cartridge. Defaults to <i>off</i>.
Note that <b>gameboy-color</b> can be used as a different spelling for this
setting.
</td></tr>
<tr><td class="cmd">
option gameboy-super, <on|off>
</td>
<td class="def">
Whether this is a Gameboy Super extended cartridge. Defaults to <i>off</i>.
</td></tr>
<tr><td class="cmd">
option gameboy-cart-type, <on|off>
</td>
<td class="def">
Specifies the cartridge type. Defaults to -1, which means the output driver
will pick the appropriate type.
</td></tr>
<tr><td class="cmd">
option gameboy-irq, <i>irq</i>, <i>address</i>;
</td>
<td class="def">
Specifies an address where an IRQ routine is stored, and requests that the
IRQ be transferred to that address when it happens. The IRQ routine must end
with a <b>reti</b> opcode.<br><br>
<i>irq</i> can be either <b>vbl</b>, <b>lcd</b>, <b>timer</b>, <b>serial</b>
or <b>joypad</b>. If left at the default value of -1 then an IRQ handler is
installed with just a <b>reti</b> instruction.
</td></tr>
</table>
<h2>Listing</h2>
<p>
By default no output listing is generated. This can be controlled by the
following options.
</p>
<table>
<thead><tr><td class="head">Listing Option</td>
<td class="head">Description</td></tr></thead>
<tr><td class="cmd">
option list, <on|off>
</td>
<td class="def">
Enables or disables listing. The listing will go to stdout by default.
Defaults to <i>off</i>.
</td></tr>
<tr><td class="cmd">
option list-file, <i>filename</i>
</td>
<td class="def">
Sends the listing to <i>filename</i>. Note this should appear before enabling
the listing.
</td></tr>
<tr><td class="cmd">
option list-pc, <on|off>
</td>
<td class="def">
Control the output of the current PC in the as a comment preceding the
line (so that a listing could be reassembled with no editing). Defaults
to <i>off</i>.
</td></tr>
<tr><td class="cmd">
option list-hex, <on|off>
</td>
<td class="def">
Control the output of the bytes generated by the source line in hex.
Defaults to <i>off</i>. If <i>on</i> then the hex is output in a comment
preceding the line (possibly with the PC above), so that a listing is still
valid as input to the assembler.
</td></tr>
<tr><td class="cmd">
option list-labels, <on|off|all>
</td>
<td class="def">
Controls the listing of labels, either:
<table>
<tr><td class="cmd">
off
</td>
<td class="def">
The default; don't list anything.
</td></tr>
<tr><td class="cmd">
on
</td>
<td class="def">
List labels at the end of the listing. The labels are output commented so that
the list could be used as input.
</td></tr>
<tr><td class="cmd">
all
</td>
<td class="def">
List all labels, including internally generated private labels for macros.
</td></tr>
</table>
</td></tr>
<tr><td class="cmd">
option list-macros, <off|exec|dump|all>
</td>
<td class="def">
Controls the listing of macro invocations, either:
<table>
<tr><td class="cmd">
off
</td>
<td class="def">
The default; don't list anything.
</td></tr>
<tr><td class="cmd">
exec
</td>
<td class="def">
List invocations of macros.
</td></tr>
<tr><td class="cmd">
dump
</td>
<td class="def">
Produce a list of macro definitions at the end of the listing.
</td></tr>
<tr><td class="cmd">
all
</td>
<td class="def">
Combine <i>exec</i> and <i>dump</i>.
</td></tr>
</table>
</td></tr>
<tr><td class="cmd">
option list-rm-blanks, <on|off>
</td>
<td class="def">
Defaults to <i>on</i>. This option causes multiple blank lines to be collapsed
down to a single blank line in the listing.
</td></tr>
</table>
<h1 id="z80">Z80 CPU</h1>
<h2>Opcodes</h2>
<p>
The Z80 assembler uses the standard Zilog opcodes, and supports
undocumented instructions.
</p>
<p>
For instructions were the Accumulator can be assumed it can be omitted, and
EOR can be used the same as XOR:
</p>
<pre class="codeblock">
xor a,a ; These are equivalent
xor a
eor a,a
and a,b ; These are equivalent
and b
</pre>
<p>
For exchange opcodes with parameters the parameters can be reversed from their
official form:
</p>
<pre class="codeblock">
; The official forms
;
ex de,hl
ex af,af'
ex (sp),hl
ex (sp),ix
ex (sp),iy
; Also supported
;
ex hl,de
ex af',af
ex hl,(sp)
ex ix,(sp)
ex iy,(sp)
</pre>
<p>
Where the high/low register parts of the IX and IY registers are to be used,
simply use ixl, iyl, ixh and iyh. Note that the assembler will accept
illegal pairings involving H and L, but these will be warned about:
</p>
<pre class="codeblock">
ld ixh,$e5
ld iyl,iyl
ld ixh,l ; This will be turned into "ld ixh,ixl" and a
; warning will be issued.
ld iyh,ixl ; This will generate an error as the index registers
; have been mixed.
</pre>
<p>
For the hidden bit manipulations that also can copied to a register, these can
be represented by adding the destination register as an extra parameter, e.g.
</p>
<pre class="codeblock">
srl (iy-1),d
set 3,(iy-1),a
res 4,(iy-1),b
</pre>
<p>
For the hidden IN instruction using the flag register the following are all
equivalent:
</p>
<pre class="codeblock">
in (c)
in f,(c)
</pre>
<p>
For the hidden OUT instruction using the flag register, $00 or $ff depending
on where you're reading, the following are all equivalent, where <i>value</i>
can be any value at all:
</p>
<pre class="codeblock">
out (c)
out (c),f
out (c),<i>value</i>
</pre>
<h2>Options</h2>
The Z80 assembler has no options.
<h1 id="6502">6502 CPU</h1>
<h2>Opcodes</h2>
The 6502 assembler uses the standard Motorola opcodes.
<h2>Options</h2>
The 6502 assembler has the following options.
<table>
<thead><tr><td class="head">6502 Option</td>
<td class="head">Description</td></tr></thead>
<tr><td class="cmd">
option zero-page, <on|off|auto>
</td>
<td class="def">
Controls the assumptions made regarding Zero Page address. Defaults to
<i>auto</i>, and can be the following values:
<table>
<tr><td class="cmd">
off
</td>
<td class="def">
The default; all addresses are assumed to be not on the Zero Page, regardless
of the value used.
</td></tr>
<tr><td class="cmd">
on
</td>
<td class="def">
Assumes all addresses are in the Zero Page, raising an error if any address is
not in the Zero Page.
</td></tr>
<tr><td class="cmd">
auto
</td>
<td class="def">
Treats addresses less than 256 as being in the Zero Page automatically. This
mode also makes the assembler perform an extra pass to guard against the
possibility of the calculation being fooled.
</td></tr>
</table>
e.g.
<pre class="codeblock">
cpu 6502
org $8000
lda $0000,x ; Produces $bd $00 $00
option +zero-page
lda $0000,x ; Produces $b5 $00
lda $1234,x ; Produces an error
option zero-page,auto
lda $00,x ; Produces $b5 $00
lda $8000,x ; Produces $bd $00 $80
</pre>
</td></tr>
</table>
<h1 id="gbcpu">Gameboy Z80 derivative CPU</h1>
<h2>Opcodes</h2>
<p>
The Gameboy assembler uses the standard Z80 opcodes where applicable.
Note that the Gameboy processor has a reduced number of opcodes, flags
and no index registers, though it has some additional instructions and
addressing modes.
</p>
<p>
For instructions were the Accumulator can be assumed it can be omitted, and
EOR can be used the same as XOR:
</p>
<pre class="codeblock">
xor a,a ; These are equivalent
xor a
eor a,a
and a,b ; These are equivalent
and b
</pre>
<p>
The Gameboy CPU has a special addressing mode used for one opcode, where the
referenced address is stored as a single byte, and used as an offset into the
top page (0xff00). This can be either triggered by using the special opcode, or
will automatically used whenever an address is accessed in the range 0xff00 to
0xffff:
</p>
<pre class="codeblock">
; These all will use the special addressing mode opcode, accessing
; memory location $ff34
;
label equ $ff34
ldh a,($34)
ldh a,($ff34)
ld a,($ff34)
ld a,(label)
ld (label),a
ld ($ff34),a
ldh ($34),a
ldh ($ff34),a
</pre>
<p>
The Gameboy CPU also supports incrementing or decrementing the HL register when
it is used as an address:
</p>
<pre class="codeblock">
; All these decrement HL after the value has been used.
;
ld a,(hl-)
ld a,(hld)
ldd a,(hl)
ld (hl-),a
ld (hld),a
ldd (hl),a
; All these increment HL after the value has been used.
;
ld a,(hl+)
ld a,(hli)
ldi a,(hl)
ld (hl+),a
ld (hli),a
ldi (hl),a
</pre>
<p>In addition the Gameboy CPU supports these extra instructions over the Z80:
</p>
<pre class="codeblock">
; Actually loads using the address $ff00 + C
;
ld a,(c)
ld (c),a
; Put the Gameboy into a low-power mode till a control is pressed.
; Note it is accepted practice to put a NOP afterwards. This may be
; due to the stop replacing DJNZ, which may still be wired to expect
; an argument. That is just a wild guess though.
;
stop
nop
; Swaps the low/high nibbles of the register
;
swap a
swap b
swap c
swap d
swap e
swap h
swap l
swap (hl)
</pre>
<h2>Options</h2>
The Gameboy CPU assembler has no options.
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