@c This is part of the GAS manual.
@c For copying conditions, see the file as.texinfo.

@ifset GENERIC
@page
@node Z80-Dependent
@chapter Z80 Dependent Features
@end ifset


@ifclear GENERIC
@node Machine Dependencies
@chapter Z80 Dependent Features
@end ifclear

@cindex Z80 support
@menu
* Z80 Options::              Options
* Z80 Syntax::               Syntax
* Z80 Floating Point::       Floating Point
* Z80 Directives::           Z80 Machine Directives
* Z80 Opcodes::              Opcodes
@end menu

@node Z80 Options
@section Options
@cindex Z80 options
@cindex options for Z80
The Zilog Z80 and Ascii R800 version of @code{@value{AS}} have a few machine
dependent options.
@table @option
@cindex @code{-z80} command line option, Z80
@item -z80
Produce code for the Z80 processor. There are additional options to
request warnings and error messages for undocumented instructions.
@item  -ignore-undocumented-instructions
@itemx -Wnud
Silently assemble undocumented Z80-instructions that have been adopted
as documented R800-instructions.
@item  -ignore-unportable-instructions
@itemx -Wnup
Silently assemble all undocumented Z80-instructions.
@item  -warn-undocumented-instructions
@itemx -Wud
Issue warnings for undocumented Z80-instructions that work on R800, do
not assemble other undocumented instructions without warning.
@item  -warn-unportable-instructions
@itemx -Wup
Issue warnings for other undocumented Z80-instructions, do not treat any
undocumented instructions as errors.
@item  -forbid-undocumented-instructions
@itemx -Fud
Treat all undocumented z80-instructions as errors.
@item  -forbid-unportable-instructions
@itemx -Fup
Treat undocumented z80-instructions that do not work on R800 as errors.

@cindex @code{-r800} command line option, Z80
@item -r800
Produce code for the R800 processor. The assembler does not support
undocumented instructions for the R800.
In line with common practice, @code{@value{AS}} uses Z80 instriction names
for the R800 processor, as far as they exist.
@end table

@cindex Z80 Syntax
@node Z80 Syntax
@section Syntax
The assembler syntax closely follows the 'Z80 family CPU User Manual' by
Zilog.
In expressions a single @samp{=} may be used as ``is equal to''
comparison operator.  

Suffices can be used to indicate the radix of integer constants;
@samp{H} or @samp{h} for hexadecimal, @samp{D} or @samp{d} for decimal,
@samp{Q}, @samp{O}, @samp{q} or @samp{o} for octal, and @samp{B} for
binary.

The suffix @samp{b} denotes a backreference to local label.  

@menu
* Z80-Chars::                Special Characters
* Z80-Regs::                 Register Names
* Z80-Case::                 Case Sensitivity
@end menu

@node Z80-Chars
@subsection Special Characters

@cindex line comment character, Z80
@cindex Z80 line comment character
The semicolon @samp{;} is the line comment character; 

@cindex location counter, Z80
@cindex hexadecimal prefix, Z80
@cindex Z80 $
The dollar sign @samp{$} can be used as a prefix for hexadecimal numbers
and as a symbol denoting the current location counter.

@cindex character escapes, Z80
@cindex Z80, \
A backslash @samp{\} is an ordinary character for the Z80 assembler.
 
@cindex character constant, Z80
@cindex single quote, Z80
@cindex Z80 '
The single quote @samp{'} must be followed by a closing quote. If there
is one character inbetween, it is a character constant, otherwise it is
a string constant.

@node Z80-Regs
@subsection Register Names
@cindex Z80 registers
@cindex register names, Z80

The registers are referred to with the letters assigned to them by
Zilog. In addition @command{@value{AS}} recognises @samp{ixl} and 
@samp{ixh} as the least and most significant octet in @samp{ix}, and
similarly @samp{iyl} and  @samp{iyh} as parts of @samp{iy}. 

@c The @samp{'} in @samp{ex af,af'} may be omitted.

@node Z80-Case
@subsection Case Sensitivity
@cindex Z80, case sensitivity
@cindex case sensitivity, Z80

Upper and lower case are equivalent in register names, opcodes,
condition codes  and assembler directives. 
The case of letters is significant in labels and symbol names. The case
is also important to distinguish the suffix @samp{b} for a backward reference
to a local label from the suffix @samp{B} for a number in binary notation.

@node Z80 Floating Point
@section Floating Point
@cindex floating point, Z80
@cindex Z80 floating point
Floating-point numbers are not supported.

@node Z80 Directives
@section Z80 Assembler Directives

@command{@value{AS}} for the Z80 supports some additional directives for
compatibility with other assemblers. 

@cindex Z80-only directives
These are the additional directives in @code{@value{AS}} for the Z80:

@table @code
@item db @var{expression}|@var{string}[,@var{expression}|@var{string}...]
@itemx defb @var{expression}|@var{string}[,@var{expression}|@var{string}...]
For each @var{string} the characters are copied to the object file, for
each other @var{expression} the value is stored in one byte, ignoring
overflow. 

@item dw @var{expression}[,@var{expression}...]
@itemx defw @var{expression}[,@var{expression}...]
For each @var{expression} the value is stored in two bytes, ignoring
overflow. 

@item ds @var{count}[, @var{value}]
@itemx defs @var{count}[, @var{value}]
@c Synonyms for @code{ds.b}, 
@c which should have been described elsewhre
Fill @var{count} bytes in the object file with @var{value}, if
@var{value} is omitted it defaults to zero.

@item @var{symbol} equ @var{expression}
@itemx @var{symbol} defl @var{expression}
These directives set the value of @var{symbol} to @var{expression}. If
@code{equ} is used, it is an error if @var{symbol} is already defined.
Symbols defined with @code{equ} are not protected from redefinition.

@item set
This is a normal instruction on Z80, and not an assembler directive. 

@item psect @var{name}
A synonym for @xref{Section}, no second argument should be given. 
@ignore

The following attributes will possibly be recognised in the future
@table @code
@item abs
The section is to be absolute. @code{@value{AS}} will issue an error
message because it can not produce an absolute section.
@item global
The section is to be concatenated with other sections of the same name
by the linker, this is the default.
@item local
The section is not global. @code{@value{AS}} will issue a warning if
object file format is not soff.
@item ovrld
The section is to be overlapped with other sections of the same name by
the linker. @code{@value{AS}} will issue an error message
because it can not mark a section as such.
@item pure
The section is marked as read only.
@end table
@end ignore

@end table

@node Z80 Opcodes
@section Opcodes
In line with commmon practice Z80 mnonics are used for both the Z80 and
the R800. 

In many instructions it is possible to use one of the half index
registers (@samp{ixl},@samp{ixh},@samp{iyl},@samp{iyh}) in stead of an
8-bit general purpose register. This yields instructions that are
documented on the R800 and undocumented on the Z80.
Similarly @code{in f,(c)} is documented on the R800 and undocumented on
the Z80.

The assembler also supports the following undocumented Z80-instructions,
that have not been adopted in the R800 instruction set:
@table @code
@item out (c),0
Sends zero to the port pointed to by register c.

@item sli @var{m}
Equivalent to @code{@var{m} = (@var{m}<<1)+1}, the operand @var{m} can
be any operand that is valid for @samp{sla}. One can use @samp{sll} as a
synonym for @samp{sli}.

@item @var{op} (ix+@var{d}), @var{r}
This is equivalent to 

@example
ld @var{r}, (ix+@var{d})
@var{opc} @var{r}
ld (ix+@var{d}), @var{r}
@end example

The operation @samp{@var{opc}} may be any of @samp{res @var{b},},
@samp{set @var{b},}, @samp{rl}, @samp{rlc}, @samp{rr}, @samp{rrc},
@samp{sla}, @samp{sli}, @samp{sra} and @samp{srl}, and the register
@samp{@var{r}} may be any of @samp{a}, @samp{b}, @samp{c}, @samp{d},
@samp{e}, @samp{h} and @samp{l}.

@item @var{opc} (iy+@var{d}), @var{r}
As above, but with @samp{iy} instead of @samp{ix}.
@end table

The web site at @uref{http://www.z80.info} is a good starting place to
find more information on programming the Z80.

