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Created a simple stylesheet, linked to it, and removed body color attributes defined there. This reduces repetition and separates style and presentation.
122 lines
4.2 KiB
HTML
122 lines
4.2 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
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"http://www.w3.org/TR/html4/loose.dtd">
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<HTML>
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<HEAD>
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<TITLE>xAsm MACRO/ENDM</TITLE>
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<link rel="stylesheet" type="text/css" href="../style.css">
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</HEAD>
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<BODY>
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<I><H2>MACRO<BR>
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ENDM</H2></I><HR>
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<P>One of the best features of an assembler is the ability to write macros for it. Macros also provide a method of passing
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arguments to them and they can then react to the input using IF-constructs.<BR>
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<BR>
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<TABLE BORDER=0 BGCOLOR="Black" CELLPADDING=8 WIDTH="50%">
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<TR>
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<TD><FONT COLOR="#00FF00">
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<PRE>MyMacro: MACRO
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ld a,80
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call MyFunc
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ENDM</PRE>
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</FONT></TD>
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</TR>
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</TABLE>
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<P>The above example is a very simple macro. You execute the macro by typing its name.<BR>
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<BR>
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<TABLE BORDER=0 BGCOLOR="Black" CELLPADDING=8 WIDTH="50%">
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<TR>
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<TD><FONT COLOR="#00FF00">
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<PRE> add a,b
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ld sp,hl
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MyMacro ;This will be expanded
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sub a,87</PRE>
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</FONT></TD>
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</TR>
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</TABLE>
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<P>When the assembler meets MyMacro it will insert the macrodefinition (the text enclosed in <B>MACRO/ENDM</B>).
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<P id="labelsuffix">Suppose your macro contains a loop.<BR>
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<BR>
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<TABLE BORDER=0 BGCOLOR="Black" CELLPADDING=8 WIDTH="50%">
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<TR>
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<TD><FONT COLOR="#00FF00">
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<PRE>LoopyMacro: MACRO
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xor a,a
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.loop ld [hl+],a
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dec c
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jr nz,.loop
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ENDM</PRE>
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</FONT></TD>
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</TR>
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</TABLE>
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<A TARGET="#labelsuffix"></A><P>This is fine. That is, if you only use the macro once per <A HREF="labels.htm">scope</A>. To get around this problem there is a special label string equate called <B>\@</B> that you can append to your labels and it will then expand to a unique string.
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<B>\@</B> also works in <A HREF="rept.htm">REPT-blocks</A> should you have any loops there.<BR>
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<BR>
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<TABLE BORDER=0 BGCOLOR="Black" CELLPADDING=8 WIDTH="50%">
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<TR>
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<TD><FONT COLOR="#00FF00">
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<PRE>LoopyMacro: MACRO
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xor a,a
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.loop\@ ld [hl+],a
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dec c
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jr nz,.loop\@
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ENDM</PRE>
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</FONT></TD>
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</TR>
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</TABLE>
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<H4>Arguments</H4>
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<P>I'd like <I>LoopyMacro</I> a lot better if I didn't have to pre-load the registers with values and <I>then</I> call it.
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What I'd like is the ability to pass it arguments and it then loaded the registers itself.
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<P>And I can do that. In macros you can get the arguments by using the special macro string equates <B>\1</B> through
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<B>\9</B>, <B>\1</B> being the first argument specified on the calling of the macro.<BR>
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<BR>
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<TABLE BORDER=0 BGCOLOR="Black" CELLPADDING=8 WIDTH="50%">
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<TR>
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<TD><FONT COLOR="#00FF00">
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<PRE>LoopyMacro: MACRO
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ld hl,\1
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ld c,\2
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xor a,a
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.loop\@ ld [hl+],a
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dec c
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jr nz,.loop\@
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ENDM</PRE>
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</FONT></TD>
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</TR>
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</TABLE>
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<P>Now I can call the macro specifying two arguments. The first being the address and the second being a bytecount.
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The macro will then reset all bytes in this range.<BR>
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<BR>
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<TABLE BORDER=0 BGCOLOR="Black" CELLPADDING=8 WIDTH="50%">
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<TR>
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<TD><FONT COLOR="#00FF00">
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<PRE> LoopyMacro MyVars,54</PRE>
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</FONT></TD>
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</TR>
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</TABLE>
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<P> You can specify up to nine arguments when calling a
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macro. Arguments are passed as string equates. There's no need to enclose them in quotes. Parameter passing has changed a bit since v1.03 in that an expression will not be evaluated first but passed directly. This means that it's probably a very good idea to use
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brackets around \1-\9 if you perform further calculations on them. For instance if you pass 1+2 as the first argument and then do
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<P><TABLE BORDER=0 BGCOLOR="Black" CELLPADDING=8 WIDTH="50%">
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<TR>
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<TD><FONT COLOR="#00FF00">
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<PRE> PRINTV \1*2
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</PRE>
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</FONT></TD>
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</TR>
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</TABLE>
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you will get the value 5 on screen and not 6 as you might have expected..<BR>
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<P>Note that a colon (:) following the macro-name is required. Macros can't be exported or imported. It's valid to call a macro from a macro (yes, even the same one).<BR>
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<H3>See also:</H3>
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<UL>
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<LI><A HREF="shift.htm">SHIFT</A>
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</UL>
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<BR><HR>
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<FONT SIZE="-1"><I><P ALIGN=RIGHT>Last updated 02 July 1997 by <A HREF="mailto:surfsmurf@matilde.demon.co.uk">Carsten Sorensen</A></P></I></FONT>
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