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rather time consuming, and a waste
of source file space to keep keying in
the same code. Instead you could
define it as a macro definition called
CENTRE - to achieve this type the
commands as you would a normal
source file, and save the file with SAVE
"CENTRE",8.
Each time you wish to use the given
instructions instead of typing out the
same code you can 'call up' or 'invoke'
the macro 'CENTRE' and the instructions
LDX # $10, LDY #$ 10, JSR
SEFF0 will be generated into your
source file. See the section on how to
invoke the macro files, and add them
to the macro library.
Added Macro Features
A couple of features are included to
make the macro definitions more
meaningful. The first feature is to allow
true parameter passing upon invoking
a macro.
parameter Passing in a
Macro Definition
The macro definitions can accept
parameters by using the ' character
to preceed a parameter number
between 0 and 9.
eg) LDA / 0
STA/ I
in the macro definition would change
/0 into the text passed by parameter
0, and / 1 with parameter 1.
See the section on macro invokation
for more details of how to pass
parameters within macros.
Localised Symbols
All labels within a macro definition
will be read in as a local symbol, this
is achieved by adding a unique 2-digit
code to the symbol within the definition.
e.g. the symbol LABEL! within
a macro definition will be given as
ABLABEL I on the first 'call' to the
macro, ACLABEL I the next time, etc,
this is so that the symbol LABEL' is
not redefined everytime a macro is
invoked, and also direct references can
be given to labels within individual
macros.
Every reference within the macro
definition to a label automatically
refers to one within a particular macro
(a local reference). If you wish to refer
to a label outside of the current macro
C64 PROGRAMMING
definition you must signify that it is
a global reference - this is achieved
by prefixing the label with a full stop.
The following is the source inside
a macro definition:
BEQ LOOP ! refers to the label
'LOOP' inside the current macro
definition.
JMP .MAIN ! refers to the label
'MAIN' outside of the current macro
definition.
Adding a Macro Definition to the
Macro Library
In order to invoke any macro it must
first be stored within the macro library.
A previously saved macro definition
can be added to the library by prefixing
the macro name with a E, symbol:
10 EMACRONAME
Note that there is no space between
E and the filename. The macro definition
must be given to the macro
library BEFORE it is invoked.
Listing the Files in the Macro Library
To summarise what macro definitions
are present in the macro library you
can view the macro directory with the
use of the library you can view the
macro directory with the use of the
editors •IVI' command,
Invoking Macros
This is the term used to expand the
macro definitions into the source file.
Once a macro definition has been
stored in the macro library it can be
invoked in the source file by using the
symbol to preceed the macro
filename to be invoked.
10 imachroname ! adds the macro to
the macro library
20 macroname ! invokes (expands) the
macro
Parameter Passing During Macro
Invocation
The macros to be expanded can be
called up with parameters as disucussed
in the section on macro
definitions.
To invoke the following macro
definition:
10 LDAtt/ 10
20 STA/ 1
Save it to disk with SAVE
"POKE, MAC",8
The above example is to define a
rather simple POKE x,y type of macro
definition but servies its purpose. Once
it is saved type NEW to clear the
current source file and type in the
following:
10 *$C000 ! sets origin
20 f.POKE.MAC ! gives definition to
macro library
30 POKE.MAC 5,53280 ! pass the
poke value, address
40 RTS
It can be seen that parameter 0 is
5 (the source will now contain LDA
5), and parameter I is 53280 (source
contains STA 53280)
A parameter can take any form
whatsoever, °Nodes; varius operands,
or any valid expression. Each parameter
is separated by a comma wso if
you are passing text, as in "HELLO,
MY NAME IS" the comma would tell
the assembler that it is the end of that
parameter so be careful!
The number of parameters allocated
to a parficular macri as 10 (0-
9), however more than this is allowed
if ASCII codes which follow "0"-"9"
are given, but 0-9 should be used as
standard. Because all labels within a
macro definition are operated on as
localised, any parameter passed to it
will need to prefixed with a full stop
if they refer to a global label outside
of the definition.
Example of a Top Level Source File
10 RED = 2 ! global label outside of
a macro definition
20 COLOUR .RED ! prefix with
a as we are using the global label
RED within the macro definition.
You will he told if you try to invoke
a macro that is not present in the
macro library. If a parameter is
required by a macro definition and one
isn't given on invoking it, a
'PARAMETER MISSING' error will
be issued. This is because no comma
will be looked for (as it is param.0)
and data that was expected to be in
the buffer will be used. The above is
of course a rarity, but worthwhile to
mention. Any parameter given to a
particular macro definition will only
be verified once it has been expanded
into the source file.
Thirty Six Y O U R COMMODORE