Larry's ACTION! Tutorial
was a monthly addition to the SPACE
The tutorials were written by Larry Serflaten. Larry wrote a total of twenty-one tutorials.
The first appeared in the January 1995 newsletter and the last appeared in the March 1996 newsletter.
With the first tutorial Larry granted permission to distribute any portion or all of his monthly contribution.
|1. The Beginning||January 1995|
So, you own an ATARI computer, now what?
To more than a few slap-happy owners, the
answer is a robust;
"Bring on the GAMES!"
Games are programs. Without any new
programmers for the Atari, we won't be
seeing many new games. (Period!)
Without twisting any arms, perhaps you
know someone who wants to learn to program
but doesn't have the means to go out and
purchase a new Pentium machine with all
the books and software needed to begin.
You might steer him/her toward learning to
program an ATARI!
If you use a little tact, you could point
out that all computers have some things in
common,(Memory, Address/Data busses, Video
display, Keyboard, and a processor to
control it all.) also that skills learned
on the Atari can lead to a quicker
understanding of the procedures needed to
program the bigger machines.
With the permission of the Editor, I will
attempt to help the fledgling programmer
overcome some of the hurdles in learning a
Action! This language is similar to
PASCAL and C. I like it because it is very
fast, compared to BASIC, and is easier
to work with than ASSEMBLY or MAC 65.
The Action! manual was not intended to
teach the user how to program. It is a
reference manual of all the capabilities
of the system. I found it difficult to
understand at first, which delayed my
getting involved with it for some time.
The first hurdle to overcome, (for me
anyway!) was to make the decision to try
to learn it. You might say it was the
biggest hurdle because after making that
initial decision, all the other hurdles
were very manageable.
I intend to follow the Action! manual as
a guide to topic progression. In order
to program in Action!, you have to have
the cartridge.(See below) Chances are you
have the manual as well. I would also
like to solicit your questions. We are
not all on the same level, so using a
little space to answer your questions will
allow more advanced users to progress.
You can send E-mail to me (Larry S) on the
SPACE BBS containing your questions. If
you are a registered user, I will reply
with E-mail. If I think others would
benefit from reading your questions, I
will include them at the end of future
We have to begin somewhere, so here is a
little synopsis of what will be coming in
First, I will lightly discuss the Editor,
Monitor, Language and Compiler to get the
real beginners familiar with loading and
running Action! source code. Then I will
discuss the same topics in finer detail,
adding the Library of supplied routines.
After that, its up to you. If there is
interest enough to warrant continuing
further with programming algorithms,
tricks and other such advanced concepts, I
will be happy to comply.
That being the first installment, I hope
I have whet your appetite for our next
The ACTION! cartridge is currently
available from CSS for $44.95 + $5 S/H.
Order line PH# is (716) 429 5639.
|2. Hello World||January 1995|
Occasionally, I must refer you to text in
the manual. I must also be brief. You
will find explanations here, when the
manual is a bit hard to understand. I
will use the same keystroke and command
notations as the Action! manual, whenever
possible. Because of different editions
of the Action! manual, I will use the
section headings when referring to text in
the manual. To find where the text is, I
suggest you make book tabs that locate
each of the Table of Contents' in the
different parts of the manual. On these
tabs, print the name of the parts of the
Action! system that the tables refer to.
You may want to make a big tab for the
Error codes appendix, that seems to be the
tab I used the most!
Also, specifying a file name is dependant
upon the DOS you are using. A file name
has 2 parts; 1) An 8 letter file name, and
2) A 3 letter file extension. There are a
few DOS's that allow sub-directories. To
allow for variances in the DOS types, the
file NAME will include the both the name
and extension. The device ID, and/or each
level of sub-directory will be named the
file PATH. The manual uses the term
'filespec' and in some cases 'filestring'
to include both the file path and file
name. Using a Backus_Naur type method of
declaration, the relationship between
file spec, path, and name is as follows:
OPEN(chan, <filespec>, mode, aux2)
filespec = <filepath> : <filename>
This means you must use a proper file
path, then a colon (:), then a proper
filename. To help explain this type of
symbolism (as used in the manual),
filepath could be further broken down to:
<device ID> [|: : <sub-directory>:|]
Device ID is the one letter identifier for
whichever device you are addressing (D for
disk drive). To denote an optional
parameter, I will use the '[' and ']'.
The |: and :| indicate you can repeat
whatever they enclose, one or more times.
The declaration from above now means; you
must use a proper device ID, then you may
optionally include the colon and a sub-
directory name, and you can repeat the
colon and sub-directory name as is needed
(or desired). The manual breaks it all
out, so that the construction of the
<filespec> would be:
<device ID> [|: :<sub-directory>:|] : <filename>
These symbols are explained and used in
the Language section, but are included
here for those of you who may be reading
ahead, and to get them explained at the
The Editor is that part of Action! that
first appears when you boot up the system.
The Editor will read and write text files,
as well as allow you to create or edit
text. If you desire, you can split the
text editing portion into two sections,
called windows. This feature allows you
to read in two files at one time, useful
for including portions of one file into
another! The Monitor is the part of
Action! that gives you control over the
rest of the Action! system. Take time to
read about the Editor and Monitor in the
first few sections of the manual.
Go ahead and 'get your feet wet' by typing
in the indoctrinating "Hello World."
program found at the start of the manual.
(See "How To Write and Run an Action!
Program") The manual leads you step by
step to help get your first program typed
in, compiled, and run. In "Text File I/O"
(Editor section) you can read about saving
and loading files from the disk.
No questions yet, next month a little help
with error correction, including typos the
manual has, and typos you may yet make.
|3. The First Mistake||February 1995|
Let's begin with your computer on, and the
HELLO WORLD program in the Editor. Add or
type in the follow text;
PrintE("End of program.")
Now press <CNTRL> <SHIFT> 'M' to get to
the Monitor. Enter 'C' to compile the
program. You will then be exposed to a
compilation error. At this point, the
program will not run. Note the Error
number and open your manual to the Error
Code Appendix. You can try to guess what
the error is if given the correct line,
however, sometimes you are not given the
correct line and you must decide what to
look for by the description supplied in
the Error Code explanation.
If text was displayed in the Monitors'
message area, the cursor would be moved to
the start of that same line. If no text
was displayed, the cursor is right where
it was when you left the Editor. In my
case, I had no text line displayed in the
Monitors message area, only the error
number. Your cartridge may be a different
version, and act slightly differently.
The manual explains this error as an
Illegal assignment. It is also an Illegal
function call, for which there is no other
error number. In my manual I have added
in the words "Jump should be Jump()" to
remind me to look for this type of error
too. Other than this ommission, I believe
all the error code explanations are right.
To correct the error, add the parenthesis
after the word "stop" ("stop()") in the
'hello' procedure, then return to the
Monitor to compile it again. It should
compile correctly now, if it doesnt,
recheck your text to find any mistakes.
If everything is correct, go ahead and run
it. Everybody makes mistakes, especially
when first learning the language. Here
are the typos you should be aware of in
the August 1983 Action! manual:
- = This is the line to look for.
+ = This is how it should be.
> = Correct the notes for this line
MONITOR / RUN - Program Execution
>RUN "<filespec>" only works when used
on programs saved from the Editor. (When
it is still in text form.)
-RUN PrintE() <RETURN> does not work.
+XECUTE PrintE() <RETURN> is correct.
LANGUAGE / Arithmetic Expressions
>TECH NOTE Using '*', '/', or 'MOD' will
not work correctly on large CARD values.
LANGUAGE / Record Manipulations
-TYPE idinfo=[BYTE level,
-TYPE idinfo=[BYTE level (omit comma)
LANGUAGE / Advanced use of Extended Types
The pointer will point to the next record
not the end of the array.
>In the main procedure;
-"mode=InputB()" won't work correctly.
+"mode=GetD(7)" works fine.
LIBRARY / The PUT Procedures
-PROC PutDE(BYTE channel, CHAR character)
+PROC PutDE(BYTE channel) will compile.
LIBRARY / BYTE color
>For Graphics(0) and text windows:
+Chr. luminance (color number = 1)
+Background (color number = 2)
LIBRARY / PROC Fill
>col and row must be the numbers of the
lower LEFT corner of the box.
LIBRARY / PROC SCopy
>The description is wrong, DEST should be
dimensioned larger than source, or else
identify an array with enough space.
While in the Monitor, enter the line:
The '?' requests the Monitor to display
the contents of a memory address. My
45056,$B000 = 6 $0136 54 310
This means I have version 3.6 which is the
last version I am aware of. If yours is 7
or greater, LET ME KNOW
Until next time!
|4. Sing-a-Long!||February 1995|
One more aid in correcting errors is the
use of the List option during compilation
of your program. To use this option, you
can go to the Monitor and enter 'O' for
the Option Menu. Continue pressing RETURN
(4 times) until the prompt "List on?" is
displayed, then enter 'Y' <RETURN>. This
option tells the compiler to list the
program in the Monitor message area, as
each line is being compiled. If it does
encounter an error, the listing of the
program stops in the approximate location
of the error. Whatever caused the error
may be listed on the screen, plus all the
preceding lines that compiled before the
error. This can narrow your search down
to about 22 lines of text, instead of how
ever many lines there are in your program.
Using the List option does slow down the
compilation process. You can use it
dynamically (you can turn it on and off)
during the compile process by including a
'SET List=1' (on) and 'SET List=0' (off)
in the text of your program. Try this out
to see how it performs. Here is a short
program to finish off the section on the
Action! Editor and Monitor;
PrintE("You say good-bye,")
PrintE("and I say ""hello!""")
PrintE("PRESS ANY KEY;")
do until ch<255 od
do until ch<255 od
This example gives an indication of why
the parentheses are needed in any call to
a procedure or function. (Remember Error
10 from the last lesson?) Type it in just
as it appears, compile, and run it. In
this example, the word 'song' is used both
as a procedue name and as a variable.
The only distinction between the two uses
are the parentheses following the variable
song=verse1 ; as a variable
song() ; as a procedure
song()=verse1() ; will not compile
Here is another example program:
PrintE("KEYBOARD TEST PROGRAM")
PrintE("Press any key; Esc=exit")
while ch=255 do od
PrintF("ch=%U atachr=%U (^[%C)%E",tmp,
The above example illustrates one method
of testing for a keypress. In the main
procedure, the BYTE variable 'ch' was used
to test for a keypress. The operating
system from ATARI uses one address to hold
the keyboard value of the most recent key
pressed. From this location the computer
can tell when you have pressed a key, and
will then translate it to ATASCII. The
address of this location is 764 or $2FC.
Action! allows the assignment of addresses
to variables, arrays and procedure names.
By declaring the variable to be residing
at address 764, the program can watch for
any keypresses, just as the computer does.
When no key has been entered, and after
each translation the address will be set
at a value of 255.
Location 763 holds the ATASCII value of
your keypress, after it has been entered
Because the GetD(7) statement will reset
ch to 255, tmp was used to temporarily
store the value so that it may be used
in the PrintF statement. You can use this
example to compare the ATASCII values with
the actual keyboard values.
Next month, Vo-cab-u-lary!
Last months PrintF, in KEYBOARD TEST, does
not need ^[ between the ( and %C. They
got printed instead of the Esc character.
In the LANGUAGE section of the ACTION!
manual is a listing of the vocabulary of
ACTION! system. The words and symbols are
listed in alphabetical order, I will list
them by function;
DECLARATIONS- Used in declaring the
procedures, functions, or variables;
ARRAY -Preceded by BYTE, CARD or INT to
declare a list of data
BYTE -Declares an 8 bit variable
CARD -Declares a 16 bit variable
CHAR -Same as BYTE
DEFINE -Allows substitution during compile
FUNC -Preceded by BYTE, CARD or INT to
indicate the start of a function
INCLUDE-Adds text from a file, to program
INT -Declares a 15 bit variable with a
sign bit as the 16th bit
MODULE -Indicates the start of global
POINTER-Preceded by BYTE, CARD or INT to
declare a variable reference
PROC -Indicates the start of a procedure
RETURN -Indicates the end of a procedure
RETURN(x) the end of a function
SET -Alters memory during compile
TYPE -Declares a Iist of mixed data
= -Used in DEFINE and SET to assign
$ -Indicates Hexadecimal notation
^ -Contents of a Pointer
@ -Address of a variable
. -TYPE reference
[ ] -Start / End of data block
" -String contents (delimiter)
' -Character conversion to value
; -Remarks (delimiter)
PROGRAM CONTROL-used to structure or
control program execution;
DO -Start of program loop
ELSE -FALSE condition of IF, ELSEIF
ELSEIF -Dependant IF conditions
EXIT -Exit from program loop
FI -End of IF, THEN, ELSE conditions
FOR -Enables loop parameters
IF -Conditional expression
TO -upper limit of FOR loop
UNTIL -Conditional EXIT from loop
WHILE -ConditionaI entrance to loop
( ) -Precedence setting parenthesis
OPERATORS- Used in program statements to
alter or combine variables;
AND -Logical AND
LSH -Bit-wise left shift
MOD -Remainder after division
OR -Logical OR
RSH -Bit-wise right shift
XOR ! -Bit-wise exclusive OR
+ - * /-Plus / Minus / Times / Divide by
& -Bit-wise AND
% -Bit-wise OR
= -Assigns equality
<> # -Not equal to
> -Greater than
>= -Greater or equal to
< -Less than
<= -Less or equal to
MODULE BYTE ARRAY
Note= [ 32 16 24 16 24 16 40 ],
Delay=[ 30 8 55 6 8 6 60 ]
PROC Wait(BYTE jif)
WHILE rtclk<jif DO OD
BYTE ARRAY Audio(8)=53760
FOR c=0 to note_count-1
Audio(2)=Note(c) LSH 1 +1
When you have this typed in, COMPILE it,
then if there are no errors, WRITE the
text file to disk. You can alter the
Notes and Delay times, but note_count must
equal the number of elements in Notes and
Delay. If you make something good, write
the compiled code, and send it to friends
who can simply load it from DOS!
From the top, programs in Action! are made
up of procedures and functions which are
called upon to do portions of a programmed
task. Usually, the parts of a program
that must be done repetitively, are coded
in separate procedures and called when
needed. Also, certain tasks that are
common among all programs, are also often
written as separate procedures and then
included in each program as desired. The
reading of the keyboard, may be an example
of a task that could be written as a BYTE
function, and included in any program that
needs user input from the keyboard. The
Action! system makes re-using routines
very easy to do.
Following along with the Action! manual,
Language section, the manual uses special
notations which you should read about. You
might remember seeing them from an earlier
issue. Next comes Fundamental Data Types
which are BYTE, CARDinal and INTeger type
variables or constants. It may help to
remember, the variables invariably change
during program execution, while constants
consistently remain the same. A 'score'
variable might always be changing while
a constant number '5' will not.
To let Action! know you want to use a
named variable, you must declare it using
one of the fundamental types.
Both 'w' and 'x' are 8-bit values. They
use one memory location to store values
in. Their value may be 0-255. The CARD
'y' is a 16-bit variable, it uses two
memory locations in the 6502 LSB/MSB
format. That is, if 'y' is assigned to
address 1536, (Ex CARD Y=1536) then the
least significant byte will be in address
1536 while the most significant byte will
be in address 1537. CARDs hold any value
from 0 to 65535. INTeger variables are
15-bit values, with the most significant
bit used as a sign bit. INTegers hold the
values from -32768 to 32767.
As seen before, when declaring variables,
you also have an option to assign that
variable to a specific address. Another
option allows you to assign a value to it
at compile time.
BYTE ch=764 ; assigns an address
BYTE spd= ; assigns a value
You need to use some sort of compiler or
numeric constant in the assignment option.
Any numeric or compiler constant works!
This can lead to some interesting results:
PrintE("LSB/MSB program O=exit")
Print("Enter a number >")
PrintF("%U > LSB=%U MSB=%U%E",
num, lsb, msb)
In this program, the variable 'num' is
assigned the same addresses that are used
for 'lsb' and 'msb'. Once 'lsb' has been
declared, its address becomes "fixed", the
'lsb' identifier is assigned a specific
address. Because its address is now a
compiler constant, it may be used later,
where ever a compiler constant is allowed.
Its the fixed address that is used in the
declaration of 'num'.
As you can see from above, the compiler
usually ignores any spaces you may want to
use. An exception to this is while trying
initialize a string.
Read the LANGUAGE section of the Action!
manual, typing in their program examples.
This will get you familiar with using the
Editor, Monitor, Compiler and language.
I am still looking to answer your own
questions. If you have any questions, send
them to me on SPACE BBS, or send a note to
the SPACE address including a line with
the words 'ATTN: Larry S' on the outside
of the envelope.
|7. Lets Start Programming||April 1995|
Writing programs is hard work! To get the
most out of your efforts, take a little
time to plan out your schedule. The chart
below will help you organized your program
to allow you to create even large programs
in a few short hours. Typing and testing
may take somewhat longer....
PROGRAM DEVELOPMENT CHART
- Decide what the inputs and outputs of
the program will be.
- OutIine the major tasks that need to be
done in the order they are to be done.
- If there are many decisions to be made
by the computer, deveIop a flowchart.
- Divide each task into its component
parts and look for similarities.
- Group the simiIar tasks together to
determine which can be combined.
- Develop a memory map of the computer,
showing where in memory the different
parts of the program are to reside.
- Type in/write the MAIN procedure first.
Fill out the rest of the program,
testing each newly added routine for
errors and accuracy.
I will use this chart to write a function
that will add two strings of numbers.
Assuming I have a game where a player may
score in the milIions. I want a routine
that will increase the score beyond the
- For inputs, I will send it the current
score, and a string containing the
amount of increase: AddTo(score,"500")
The output should be placed back into
the score string before returning.
- I must first find the least significant
digit of both strings, add these, store
the result and calculate a carry if
necessary. I must then add, store, and
carry the next set of digits, and the
next, until there are no digits Ieft to
add. Finally, the new value must be
placed back into SCORE.
- There are not that many decisions, the
flowchart can wait for another issue.
- This is a component task: increment.
There are repetitive tasks, but they
are specifically related to adding two
strings. For now, I don't see any
advantages to breaking them down, and
writing them as separate routines.
- Nothing to group, its only one routine.
- SCORE and the other string are provided
in the call, I will need a place to
hold the results until the operation
is done. This string can simply be
assigned a location by ACTION!
PROC AddTo(BYTE ARRAY s1,s2)
BYTE ARRAY result(15)
d1=s1(0) ;LSD (digit) of s1
d2=s2(0) ;LSD of s2
IF d1>d2 THEN ;Assign LSD of result
digit=d1+1 ;s1 is longer
digit=d2+1 ;s2 is longer
result(0)=digit ;Storage string length
result(1)='0 ;MSD just in case
carry='0 ;clear carry
WHILE d1>0 OR d2>0
result(digit)=carry ;Handle carry
IF d1>0 THEN ;Still more s1
d1==-1 ;Next digit
IF d2>0 THEN ;Still more s2
d2==-1 ;Next digit
IF result(digit)>'9 THEN
carry='1 ;Calculate carry
digit==-1 ;Move to next digit
result(1)=carry ;Store carry
IF carry='0 THEN ;Delete leading 0
FOR i=1 TO result(0)-1
s1(0)=i-1 ;New length
ELSE ;carry=1 so copy as is
FOR i=0 TO result(0)
It's YOUR turn!
|8. Adding To Our Understanding||April 1995|
If you had trouble using the AddTo routine
in last months issue, it may be due to not
supplying enough space to store the score
string. Here is a test example that will
BYTE ARRAY score(20)
score(0)=1 ;Initializing score to 0!
FOR i=0 to 20
This month, we will again use the PROGRAM
DEVELOPMENT CHART to make a new routine
that will multiply two strings. As you
might guess, we will make use of the AddTo
routine from last month!
- Like before, the routine will get two
string parameters and store the result
in the first parameter.
- To multiply, the 1st parameter must be
added to itself as many times as are
indicated in the ones digit of the 2nd
parameter. Moving to the tens digit
of the 2nd parameter and a value that
is ten times greater than what the 1st
parameter was, we again add according
to the value in the tens place, etc.
- Flowcharting comes later when there
are more conditions to consider....
- We have a similarity, we need to add
one string to another, luckily it is
already available. (Reusable code!)
- This is only a routine, not too many
similarities to try to group them yet.
- Again we can let ACTION! handle string
(READ in AddTo in this area)
PROC MultiplyS(BYTE ARRAY s1,s2)
BYTE ARRAY temp(smax)
FOR i=0 to s1(0)
temp(i)=s1(i) ;Init temp for adding
s1(i)='0 ;Clear result
s1(0)=1 ;Init result
digit=s2(0) ;Ones place
inc=temp(0) ;*10 increment
value=s2(digit)-48 ;value of digit is
WHILE value#0 ;the # of additions
digit==-1 ;Next digit
inc==+1 ;Increase temp * 10
temp(0)=inc ;by adding to length
temp(inc)='0 ;and storing a new 0
To help manage the string sizes, I have
included a DEFINE statement at the start
of this procedure. This statement must
manage the string in AddTo also. To
allow for this, change the declaration
line 'result(15)' to 'result(smax)' in
the AddTo procedure.
DEFINE simply substitutes whatever is in
quotes with every occurrence of the string
listed in the DEFINE statement. The
result of this is that the compiler will
use 100 every time it finds smax, this
makes for easy editing, without having to
parse through the entire program looking
for places that may need a new value!
Changing smax once, effects all other
occurrences, pretty neat eh?
Of course we want to see it in ACTION!
BYTE ARRAY sc(smax)
sc(0)=1 ;MUST be initialized!
FOR i=0 TO 15
Hey! This could be the start of a huge
calculator! Adding subtract and divide,
and a temporary register for complex
equations, and there it is! Hmmm....
Next month, we get back to BASICs!
|9. A Wealth Of Knowledge||July 1995|
If you felt a little challenged these past
few issues, don't be alarmed. I want you
to have useful examples, which can be used
in your own programs, even if you lack the
skills to develop sophisticated software.
Time spent doing things you know how to do
will increase your skills, as well as your
library of reusable code! I will supply
a few useful routines you can use in your
programs, which you can study and learn
from. Not to say I am the worlds best
programmer, but I do offer help!
We have covered the Editor, Monitor, and
Compiler. Open your manual to the Library
table of contents. If you have tried to
use the BASIC language, you may recognize
many of the supplied procedures and
functions. In fact, the library is simply
a collection of PROC's and FUNC's that may
help the BASIC programmer shift to using
ACTION! It is the programmers option, to
use any of these routines, or none at all.
All of them are included in the cartridge.
Turn to the page containing the EOF(8)
routine. Lets design a test to see it
operate. With your Editor cleared, make
a list of 2-3 words and save it with the
filename of "D:TEOF". Clear your Editor
and type in this test routine:
Compile and run this program. Is the list
exactly as you typed it in? Mine has a
funny little character at the end. If
yours does too, you will benefit from this
next routine. Now above the MAIN routine,
BYTE FUNC SOF(BYTE a)
BYTE POINTER bp
bp=((a&7) LSH 4) + 835
IF bp^=3 THEN RETURN(1) FI
(Main should be here!)
Now change the EOF in the Main procedure,
to SOF and compile and run it. Isn't that
better? Since you now may have a better
routine, rename SOF to EOF and change the
Main procedure back to EOF. Try it again.
Did you notice the funny extra character?
Naming the new routine 'EOF' will in
effect replace the EOF array as used in
the library. You can do this for any of
the routines. The names of the procedures
and functions in the library ARE NOT
RESERVED names. In fact, this is why a
runtime library allows you to make
programs that do not need the cartridge.
The supplied routines are called instead
of the library routines of the same name.
Take the time to look over the library,
studying how to call each routine. Write
tests for the harder ones to be sure you
understand their usage.
For those of you wanting to dig a little
deeper into programming, type this in:
After compiling this short procedure, use
"* See" in the Monitor to see the compiled
machine language code.
You can use the '*' (Dump) option in the
Monitor to check out how the ACTION!
system changes your text into machine
language. By typing in short programs,
you can manually disassemble the code to
help you learn machine language. It will
come in useful when you have larger
programs that you want to optimize. You
can expect to cut out about half of the
machine code that ACTION! uses, if you
want to do some optimization.
Thats the ACTION! system, next month we
take a brief look at the ATARI computer
system. After a few key points about the
ATARI computer, we can then, finally, get
to creating our own library.
|10. The Effect Of Change||July 1995|
To program your Atari, you really must
understand how the memory is organized,
how it is used, and which memory locations
cause what effects.
A real good book on this subject is;
MAPPING THE ATARI from Compute! Books.
Basically, your computer has RANDOM ACCESS
(RAM) and READ ONLY (ROM) memory. RAM is
used by the applications to hold program,
and user data. ROM is used by the
manufacturer to hold the OPERATING SYSTEM
(OS), and special purpose chips. The
chips may allow user access, but generally
you can not write to memory locations
above 40960 ($A000-$FFFF).
The special chips perform several of the
functions necessary to talk with the
outside world. Pokey handles serial port
Input and Output (I/O) and interrupt
requests, PIA handles the controller
jacks, and ANTIC handles the video screen.
The OS contains the code and data needed
to operate these chips. The PIA and ANTIC
are actually microprocessors, the ANTIC
chip is even run by a little program!
The OS uses some RAM to hold the variables
it needs to use; margins, colors, cursor
position and many other attributes change
as the computer operates. Knowing where
the OS keeps its variables allows the
programmer to alter them to produce subtle
and major changes in the way the computer
Using these variables is very easy in
Action! Simply by assigning an Action!
variable to the address of a hardware
register, or OS variable, your program
can manipulate them as needed. The OS
sometimes uses shadow registers which are
memory locations used to hold values used
in another register. Locations 704-712
are such registers. You can change these
color registers at any time, but the
change will not be seen until after a
vertical blank interrupt. If you instead
change the hardware register, the change
will take place immediately:
BYTE ch=764, random=53770,
CARD ARRAY regs=[710 53272]
BYTE POINTER bp
PrintE("Press any key to alternate")
if ch<255 then
bp=regs(toggle) ;Change registers
if toggle=0 then
else ;Toggle=1 (!)
if ch=28 then EXIT ;Esc pressed
else ch=255 ;Reset ch
wsync=1 ;Wait for sync
bp^=random & $E6 ;Dark colors only
bp=regs(0) ;Restore original
Location 710 is a shadow register of the
hardware register at location 53272.
The variable wsync is used to synchronize
the processor with the display screen.
Any time wsync is written to, the CPU is
halted until the scanning beam is at the
start of a new scan line. This program
demonstrates the difference between the
shadow and hardware register used to
give color to the background. Changing
the shadow register will change the
background color, only after the vertical
blank period (the time when the scanning
beam is turned off, going back to the top
of the screen). Changing the hardware
register will cause a color change in the
middle of displaying the screen. The new
value will take effect as soon as it is
stored (which happens every couple of
lines due to wsync). Remove the wsync
statements to see a new effect.
As this was written, SPACE BBS was in the
process of being moved to a new location.
Perhaps the best way to receive your
questions is by mail, otherwise, don't
hesitate to ask me about Action!
Next month, practical examples!
|11. Off And Running||August 1995|
One of my earliest questions was;
Why won't this program work without the
I will save you the pain of pulling your
hair out and tell you. If you want to
write programs that will run without the
cartridge installed, you must follow these
- No errors. Any error will halt your
program. You can tell if your program
has an error by running it with the
cartridge installed. If it works OK,
the Monitor message area will be clear
when you exit from your program.
- No library calls. You have to supply
all the necessary code to run. Any
call to the library will generate an
error when run without the cartridge.
- No more than 2 bytes of parameters in
any function or procedure call. More
than 2 requires a little parameter
saving routine found in the cartridge.
Thats 2 BYTEs or 1 CARD and no more.
- No MOD, multiplication, or division.
You can add and subtract to your hearts
content, but you can't try to multiply.
These also call a cartridge routine.
- No shift operations using a variable,
or using a constant larger than 4.
If you follow these rules, your program
should run without the cartridge. The two
rules I have had trouble with are 2, no
library calls, and 4, no multiplication.
How can you read the keyboard if you cant
use OPEN(4,"K:",4,0)? As shown earlier,
you can monitor address 764. How about
opening a file? Offsets depend on using
multiplication for tabular data....
Here are a few solutions to get around the
need for the cartridge. Of course you
have to write programs that wont cause an
error, number 1 is rather evident. Number
2, as you saw earlier, you can write your
own routines and use them in place of the
library calls. For the few that you will
need, this is a must. To eliminate rule
3, you can store and retrieve the needed
parameters in an array, passing only the
address of the array, and picking out the
parameters in the called routine. Number
4 is hard to eliminate, except by writing
the code needed to multiply or divide two
numbers. The same with rule 5, if you
must shift according to some variable, you
will have to write code or a routine to do
the entire shift using no more than 4
shifts at a time.
A LSH or RSH must be followed by a
constant number, but that shift can be in
a FOR/NEXT loop. If the needed constant
is larger than 4, two lines that total the
number needed may be used:
TO CODE THE STATEMENT: USE:
X= X LSH Y FOR Z=1 TO Y
DO X==LSH 1 OD
X= X LSH 7 X==LSH 4
To help you get started on your very own
library, I have adapted the multiplication
program found on page 171 in ATARI ROOTS
to Action! The major changes include the
storing of the Accumulator and X register
to $E0 and $E1 respectively. Action!
expects the value of a function to be
returned in location $A0 and $A1, these
locations were used instead of $C0, $C1.
This function will multiply two BYTE
values and return a CARD value. Often
that is enough to squeek by in a pinch!
CARD FUNC MultiplyB=*(BYTE a,x)
[$85 $E0 $86 $E1 $A9 $00 $85 $A0 $A2
$08 $46 $E0 $90 $03 $18 $65 $E1 $6A
$66 $A0 $CA $D0 $F3 $85 $A1
$60] ;$60 is a RETURN command
FOR i=10 TO 200 STEP 15
DO FOR j=0 TO 200 STEP 50
The '=*' after the word MultiplyB simply
means to omit the allocation of memory
for the parameters. Action! passes the
parameters using the accumulator and X
register. No reference was made in the
function to either 'a' or 'x' so there
is no need to reserve memory for them.
The function obtained the values directly
from the accumulator and X register.
Although the MultiplyB routine will run
without the cartridge, the Test routine
calls a library procedure. Guess whats
coming next issue!
|12. Kilroy Strikes Again!||August 1995|
These months sure take a long time, don't
they? This month we make use of the old
MultiplyB routine and add a little more
to your library!
CARD FUNC MultiplyB=*(BYTE a,x)
[$85 $E0 $86 $E1 $A9 $00 $85 $A0 $A2
$08 $46 $E0 $90 $03 $18 $65 $E1 $6A
$66 $A0 $CA $D0 $F3 $85 $A1 $60]
BYTE FUNC AscToInt(BYTE chr)
i=chr&128 ;Inverse bit...
IF chr<32 ;Conversion
RETURN(chr+i) ;Implied ELSE
BYTE POINTER bp
FOR bp=savmsc to savmsc+959
DO bp^=0 OD
PROC EchoS(BYTE ARRAY sa)
BYTE ARRAY dst
You might want to save this portion for
later use, then type in the Test program
to see it in use. These and the test
program will run, in object form, from
DOS! Make sure, then save them.
MODULE simply lets the compiler know that
you are declaring variables that you want
available to ALL FOLLOWING routines. Here
we declare a variable to use the systems
pointer to screen memory (savmsc), the
cursor X position and, cursor Y position.
MultiplyB, Hello! Reuseable code is FUN!
AscToInt is a routine that changes ASCII
to Internal code. This code is used by
the system to determine what characters to
display on the screen. Why the people at
Atari didn't simply use ASCII is not a big
concern NOW! You can use the next routine
to play around with different values. It
basically strips off the inverse bit, then
calculates the new value needed, and adds
back the inverse bit before returning.
CLS is my ClearScreen routine. Changing
the 0 to some other value will fill the
screen with a different character.
EchoS will duplicate whatever is in quotes
including non-printable characters. To
make it as fast as possible, I did not
include any error checking or alter X or
Y. With 40 bytes in a line, 'dst' has to
be Y*40 bytes from the top (savmsc). It
also has to be X number of spaces from
the left edge, then offset by 1 to align
with the incoming string. If not offset,
then 'dst(0)' would be at the X and Y
position, but 'sa(0)' is not supposed to
be printed, it holds the length of the
string. The first byte of the string is
actually in sa(1). Offsetting allows
'dst(1)' to be at the correct X and Y
position, thereby setting up a means of
direct (1 to 1, 2 to 2, etc.) assignments.
Using these routines as examples, perhaps
you can write your own Echo, EchoB, EchoI,
and EchoC. I used echo because, I saw the
name used in another program, to do about
the same thing, and because it keeps it
separate from Print and its options which
provide error and boundary checks. Of
course you'll want to test them:
EchoS("KILROY WAS HERE!")
EchoS("And he wants you to press a key!")
DO UNTIL ch<255 OD
Remember to set X and Y each time!
|13. Details, Details, Details!||October 1995|
Much of computer programming involves the
use of expressions. Action! supports
arithmetic, bit-wise and, relational
expressions. Arithmetic operators, as
their name implies, perform arithmetic
functions. Bit-wise operators are used to
manipulate values on a bit-by-bit level.
Relational operators allow for combining
variables or simple expressions to form
much more complex expressions.
Arithmetic operators (*, /, +, -, MOD) are
fairly self evident. Their use is the
same as normal arithmetic! To save space,
and your valuable attention, I wont try
to explain how to use them!
The 'and' operator '& is often used to
mask bits in a register, or limit the
number of bits in an operation.
The 'or' operator '% is often used to
add bits into a register.
The 'xor' operator '! has several uses,
to toggle bits, subtract, and may be
used to add and remove bits in a
Masking is produced by 'and'ing a value
with another value which contains each
bit set that is desired in the result:
> insures turn will only count
from 0 to 3 and then wrap around back to
0 again. Using a mask value of 10 will
not limit the count to 10. It will limit
turn to be either 0,2,8 or, 10, if that
The following is an example using alot of
bit-wise manipulation, it converts only
alpha-numeric characters to their lower
case normal video equivalents:
BYTE FUNC ToLower(BYTE a)
IF (a&$70)=$30 THEN
IF (a&$0F)<10 THEN
RETURN (a&$3F) ;Its a number
ELSEIF (a&$7F)<$41 THEN ;Too small
ELSEIF t>0 AND t<$1B THEN
RETURN(t%$60) ;Its a letter
RETURN(32) ;Too large
PRINTF(" %C%C = %C%E",27,A,B)
UNTIL A=255 OD
These are the characters that will be
accepted; NORMAL INVERSE
Numbers $30 - $39 $BO - $B9
Capitals $41 - $5A $C1 - $DA
Low case $61 - $7A $E1 - $FA
You might know that the only difference
between normal and inverse is that bit 7
is set for the inverse video characters.
Once this bit is stripped away, we can
limit our efforts to the values under the
NORMAL column. The high nibble (a nibble
is 4 bits) of every Number is a 3. We can
test for that, then a test to be sure the
low nibble is 9 or less will insure we
have a number to work with. Numbers need
no translation, once we have one, we can
simply pass it back. Returning a&$3F will
strip off the inverse bit of the incoming
There are several characters between 0 and
$41, To insure no attempt is made to
translate them, a simple 'less than' test
will eliminate them. Since the next
statement after the IF/FI is a RETURN(32),
valuable space can be saved by letting
control 'fall through' out of the IF/IF
condition as opposed to including a
RETURN(32) after the THEN.
We know the alphabet has only 26 letters.
In both CAPS and low case, the letter A
has a lower nibble value of 1. It stands
to reason that the value for Z must be 25
steps up from the value of A. 26=$1A, so
each bit of the low nibble is needed along
with one bit of the upper nibble. The
command t=a&$1F strips away all attributes
from 'a and gives us a value in the range
of 0 to 31. A previous test has taken
care of values too low to use, so we know
this is going to be a letter. If this
value is equal to or between 1 and 26, it
must be a letter. That test is performed,
and if true, the value $60 is added to it
to bring it up to the range of lower case
Next month; RELATIONAL operators.
|14. Deal Me In!||October 1995|
BYTE ARRAY shoe(52)
;INCLUDE: (From my tutorial #12)
;Global variables; savmsc
; x, y
PROC Echo(BYTE a)
BYTE POINTER dst
BYTE FUNC PickCard()
UNTIL crd<52 AND shoe(crd)<DECKS
BYTE FUNC ShowCard(BYTE a)
BYTE ARRAY pip="A23456789TJQK",
suit=",.p;" ;(Use Control key)
s=(a&3) +1 ;Mask out suit
v=(a RSH 2) +1 ;Remove suit
Echo(pip(v)%128) ;Display card
IF v<10 THEN ;Calculate value
FOR i=0 to 51 ;"Shuffle"
DO shoe(i)=0 OD
cnt=0 ;Init counter
CLS() ;Clear screen
y=O ;Init Y
x=3 ;Init X
cnt==+1 ;Increment counter
x==+2 ;Next column
UNTIL cnt=tot OR x=37
y==+3 ;Next row
UNTIL cnt=tot OR y=21
EchoS("Press any key...")
WHILE ch=255 DO OD ;Wait for keypress
UNTIL cnt=tot ;All cards out
This month you get a full blown program
to shuffle cards and display them on the
screen. This entire program can be run
from DOS. If you have not written an Echo
procedure, I have supplied one. You must
supply the routines you typed in from
issue #12. When typing in the ShowCard
function, use the card characters in the
suit string. I used printable characters
so that our editor could easily print out
the program: You must hold down Control
when typing the characters between quotes.
Some casinos use 4 decks in what they call
a shoe, for their Blackjack tables. Other
games use less. DECKS is given to allow
for an easy method of determining how many
decks are to be shuffled together.
The first relational operator is in the
PickCard function. In 4 decks of cards,
there are only 52 different cards, and
only 4 of any one card. Both conditions
must be met before the card is accepted.
The next relational operator is in the
Main procedure. I know I cant draw more
cards than are in the shoe, nor do I want
to attempt to print a card somewhere off
the screen. At the start of the loops, X
or Y is initialized. I may or may not run
out of cards while in either of the loops.
As you can see, if cnt=tot, then every
loop will be exited from. The statement;
IF cnt=tot THEN EXIT FI, would work. I
like keeping things small, adding another
IF condition would create the need for
Further discussion coming next month.
|15. A Bit Of Digression||November 1995|
Now that you have fully scrutinized the
nifty routines I included in last months
issue, you may have noticed that ShowCard
was a function, yet used as a procedure.
This is completely acceptable. When used
this way, the value returned is ignored.
You can use the ShowCard function to find
out the value of the card. Aces thru Tens
count as their pip value, while face cards
count as ten. If need be, the card itself
can be used to determine suit, in the same
manner as ShowCard.
You might also wonder why the routines
that were just a few lines long, were not
simply written into the Main procedure.
One reason is that Action! was designed
to make use of RE-USEABLE code. Any task
that may be needed repeatedly should be
in its own routine. There is a limit to
how many routines you can have, namely
1024 bytes for global variable and routine
names. The smaller names you use, the
more of them you can use. I have written
several large programs and have yet to run
out of room for the names. I usually end
up pressed for memory to hold all the
needed code. A second reason is that it
makes for more readable code. A different
programmer may want to make use of your
code. By keeping routines small, focused,
and well documented, other programmers may
be better able to reuse your code. It is
much easier to read when there are few
global variables, and each routine uses
only the variables it needs to do its
You may think Echo was a small routine,
believe me, it isn't. Translated to ML
(Machine Language) it grows dramatically.
You can benefit from substituting your own
optimized ML code for the tasks that are
repeated often. To show you how much
difference there can be, I have supplied
an optimized ML version of the AscToInt
function. This function is used several
times in one EchoS call. Each byte of
code we save counts as one cycle for each
letter in a string of characters. This
savings will result in increased response
Load the old AscToInt routine into your
Editor, compile it, and while still in
the Monitor type; ? AscToInt <RETURN>
Record the left most number to paper. Now
type; * AscToInt <RETURN> and get ready
to stop the listing using the <CNTL><1>
key combination. Stop the list when you
see a diamond after the equals sign, this
is the RETURN byte. Record the leftmost
number here and subtract the first number
from it. I find it to be 48 bytes long,
whereas, this new function does the same
thing in only 27 bytes. That works out to
about 21 EXTRA cycles needed in the code
written by Action!
Assuming a 19 byte string, on only a half
of a line of text, 400 cycles can be saved
using the new routine. Print just three
lines of text and you can expect to gain
over 2000 cycles!
BYTE FUNC AscTolnt=*(BYTE a)
[$85 $E0 ;STA $E0 Save Accu.
$29 $80 ;AND #$80 Mask out
$85 $E1 ;STA $E1 inverse bit
$45 $E0 ;EOR $E0 Gone!
$C9 $20 ;CMP $20 a<32
$B0 4 ;BCS +4 >+ Jump if false
$09 $40 ;ORA $40 | add 64
$90 6 ;BCC +6 >-|-+ Jump to RTS
$C9 $60 ;CMP $60 <+ | a<96
$B0 2 ;BCS +2 >--|-+Jump if false
$E9 $1F ;SBC $1F | |subtract 32
$05 $E1 ;ORA $E1<---+-+add Inv bit
$85 $A0 ;STA $A0 Still in Accu.
I listed it in this form for those of you
trying to optimize your own code. You can
compare the two routines, which operate
in much the same fashion. One bit of
razzle-dazzle, you may notice I didn't
clear or set the carry flag, even though I
performed branches that depend upon it.
The CMP instruction affects the carry, if
operand >= accumulator, carry is set.
Also 'SBC $1F' supposes it needed a borrow
(Carry is clear) so it takes one away
also. The total subtracted from the
accumulator is 32 ($20).
Zero page memory, used because of its high
access speed, is not hard to find. Making
efficient use of it is another matter.
Action! uses $A0-$A1 to store returned
values from functions, and, $A3-$AF to
Store parameters. I use $E0-$EF.
Next month, flowcharts!
|16. Caught In The Flow||December 1995|
Many people know how to use a map. Fewer
people know how to make one. The same
could be said for a newspaper, toaster,
baseball glove, microwave, or a flowchart.
They are all tools, used when we want to
do a specific task. When it comes time to
order and list all the logical steps and
branches of a new program, a flowchart is
your tool to gain perspective.
To demonstrate my point, I will play the
roll of plant manager, you are my shipping
process engineer. We are about to tool up
for 12 different products of merchandise.
Our automatic shelves will accept any of
the items from the end of a conveyor. You
are to design the conveyor system that
will move each item to its proper shelf.
The products will arrive from the plant on
one conveyor in random order. Each of the
12 products are differentiated by either
color, size or, weight. You get to use
scanners, scales, gates, and conveyors to
build the warehouse storage system.
Scanners measure color and size, scales
measure weight, gates divert the box to
another conveyor if the (scan/weight) test
fails. This information, combined with a
complete description of the 12 products,
will provide you with the main reason why
flowcharts are used. If you attempt to
submit a design, you will have to have a
record of it for others to inspect. You
need a piece of paper to express such a
large complicated system. A flowchart is
simply a representation of the complete
design, drawn out on paper.
Of the 12 items:
3 are black, 3 are red
3 are blue, 3 are black and red
(Scanners designed to detect black will
pass the black boxes, and the black and
red boxes also. The same for scanners
that detect red, will pass both the red
boxes and the boxes that are black and
- Black boxes are small, medium, or large.
Black items weigh 10 Lbs.
- Red has small, medium, and large boxes.
Red items weigh 10 Lbs.
- Blue has 1 large and 2 medium boxes.
One of the medium blue weighs 20 Lbs,
the other blue boxes weigh 50.
- Black and red has 2 small and 1 med.
One of the small black and red items
weighs 20 Lbs, the others weigh 50.
This brief description should give you a
different size, weight or color for each
of the twelve products.
You must now devise a path for the items
to follow using as few scanners, scales,
and gates as possible, making sure all the
items get transported to a shelf and that
no shelf has more than one type of item
stored on it. Once you have given this
some thought, try to determine the least
amount of gates, scanners, and scales you
would need to do the job. Then see if you
can reduce your plan to using only that
The perspective you gain when you build
your flowchart (floorplan) is included in
the ability to conceptualize each action
needed to accomplish the desired outcome.
The first action needed in the floorplan
is a scanner and gate to divide up the
incoming boxes of product. You can label
that action as a test and branch, but what
test would be best suited to be the first
test? There are several variables, and
perhaps a few different solutions, what is
the first thing to consider? If this sort
of problem interests you, perhaps you will
make a good programmer.
Most flowcharts consist of input/output
blocks (slanted rectangles), decision
blocks (diamonds), processing blocks
(rectangles), termination or beginning
blocks (ovals), and the lines and arrows
that connect them all. You can use this
system to solve a problem like the one
above, or you can devise your own system.
When you have completed the flowchart, you
have created an algorithm, a special
method for solving a problem. Programs
typically contain many algorithms, because
they often do many things. The test and
branch from above is a decision type
operation. Input from the plant, of
course, is input, with lines as conveyors.
The (automatic) shelf could be thought of
as a save or store process. Whatever
works for you, may be useful!
When a user has to wait for the computer
to finish processing, the computer is most
often being slowed down by many iterations
in a loop structured algorithm. The
programmer must use a good algorithm,
coupled with the speed of machine language
commands, to reduce the wait time. Moving
from flowcharts to actual machine code is
part of the programming process and is
the subject of the next issue. Advanced
users of ACTION! might want to "look in"
and give me feedback and/or assistance!
From the last issue:
The 12 different boxes of product need
11 gates to provide 12 conveyors to the
12 automatic shelves. My set of eleven
tests began with a scale weighing out
any package less than 15 Lbs. If your
solution has something different, that is
perfectly acceptable, provided it meets
the needs of the job. Basically the first
test should divide the group of products
roughly in half, but it is not mandatory.
The important part is that it performs as
required, and you can check that by using
your flowchart to see where each box
would get diverted to. The criteria was
that the boxes should end up on separate
shelves. You might imagine the supervisor
may want to invest more cash into the
system and ask you to add in the needed
equipment to reject certain boxes which
fail in a unique way, and return all
rejects on a new conveyor to the plant.
Such is the way it goes in programming,
just when you think your done, somebody
shows up and wants to change the program.
A good flowchart helps in modifying an
already complete program. With a flow
chart, the programmer can make necessary
changes to the algorithm, and can quickly
add in the needed code in the proper spot.
This is just a reminder to always document
your programs, either by the use of a flow
chart, or in the source code itself. You
never know when you may decide to add more
stuff to a finished program.
Moving from words in a flowchart, to code
on the computer can be made easy to do.
The more details included in a flowchart,
the easier it is to translate into code.
Flowcharts also help in optimization of
algorithms. Careful inspection of a flow
chart can reveal redundant loading of a
variable, or testing of a value, that may
be consolidated or reduced. Looking at
the whole process, might give insight to
a different algorithm, or method, that
will do the same thing even quicker. Some
times a better algorithm will be enough,
and should be attempted first, but there
are occasions when assembly is the best
choice. Remember you need only to rework
the code that causes a delay, or that will
make a perceptable difference. There is
no big advantage in optimizing the part of
a program that is already performing well.
As if to fly in the face of good advice,
look back at issue #12's procedures. Here
we had a few good routines that were made
even better by translating part of them to
machine code (AscToInt). EchoS has a loop
in it, one of the most basic programming
structures, and the most time consuming.
Translating this routine to machine code
will provide an example of the loop
structure as it appears in machine
First the flowchart:
- Save STRING address
- Calculate DESTINATION address
- Initialize counter
- Load byte from STRING
- Save byte to DESTINATION
- Decrement counter
- Test for end condition
- Loop to "4" until done
Now the code:
PROC EchoS=*(BYTE ARRAY S)
;1. Save STRING address
[$85 $A2 ;STA $A2 Save S LO
$86 $A3 ;STX $A3 Save S HI
$A5 $54 ;LDA $54 Y pos
$A2 40 ;LDX #40
$20 MultiplyB ;JSR MultiplyB
$A5 $58 ;LDA $58 Screen LO
$65 $55 ;ADC $55 X pos
$65 $A0 ;ADC $A0 (Y*40) LO
$85 $A4 ;STA $A3 DEST LO
$A5 $59 ;LDA $59 Screen HI
$65 $A1 ;ADC $A1 (Y*40) HI
$85 $A5 ;STA $A4 DEST HI
;3. Init counter
$A0 $00 ;LDY 0
$B1 $A2 ;LDA ($A2),Y
;START=START+1 S(0) is string Length!
$E6 $A2 ;INC $A2
$D0 $02 ;BNE 2
$E6 $A3 ;INC $A3
;4. LOOP start, load byte
$B1 $A2 ;LDA ($A2),Y
$20 AscToInt ;JSR AscToInt
;5. Store byte
$91 $A4 ;STA ($A4),Y
;6 Decrement counter
;7 & 8. Test and Loop until done
$10 $F6 ;BPL (LOOP)
;9. RETURN from whence we came
As you can see, most of this procedure is
spent setting up the parameters for the
loop. The loop itself is quite small,
only 10 bytes (Two bytes are used to
indicate where AscToInt is located). This
loop can still be optimized further, if
desired, by moving all the code from the
AscToInt routine to its proper place in
the loop. This results in eliminating the
need for jumping (using time to store
values on the processor stack and in the
program counter) which is time consuming
when done repeatedly. The code from the
AscToInt routine is needed for this loop
to function, so moving it 'in line' will
make the loop larger, but will actually
reduce the execution time.
Were you wondering how to call a procedure
using machine language? You can also call
ACTION! routines that you have written.
ACTION! passes variables using the A and X
registers, and returns function values in
$A0 and $A1.
|18. Breaking The Record!||January 1996|
BYTES, CARDS, POINTERS, and ARRAYS can be
used for most of your programming. There
comes a time when you must work with a
large amount of data, and a mixed set of
BYTES, CARDS, and ARRAYS. At times it
makes sense to organize your data so that
it may be easily processed, other times it
makes just as much sense to organize your
data for optimum use with files on a disk.
Records are used to help in both of these
Records allow a programmer to group the
fundamental data types together (BYTES,
CARDS, and INTEGERS). The grouping must
be declared before it is used. The records
become real useful when you set up a block
of memory to hold an array of records.
This is no more than a BYTE array, which
is divided into individual records, one
record right after the other. Each record
can be accessed using a record POINTER,
which steps through the array, in steps
the size of one record.
TYPE DAY=[BYTE hi,lo ;Record FORMAT
BYTE ARRAY memory(400) ;Records storage
DAY POINTER temp ;Record ID
DEFINE RECORD_SIZE="4" ;2 BYTES + 1 INT
DEFINE MAX_DAYS="9" ;99 max!
temp=memory ;# 1a
FOR i=0 TO MAX_DAYS
temp==+RECORD_SIZE ;# 1b
printE("DAY High Low Chg")
FOR i=0 TO MAX_DAYS
temp=memory+(RECORD_SIZE*i) ;# 2
PrintF(" %U %U %U %I",
You can read your manual to get further
information on declaring records. This
program is nothing special, it creates a
list of each days high and low temperature
and indicates the change of the high temp
from one day to the next. Take note,
there are two methods used to access the
records. Method #1 sets 'temp' to the
start of the storage area (1a) and steps
through each record by adding RECORD_SIZE
to 'temp' (1b) each pass through the loop.
Method #2 calculates the proper location
of each record (#2). This random access
method of locating each record is simple
to use and works well for records that
reside completely in memory.
Because each record can be accessed in a
uniform manner, the need for special data
handling code is reduced. To give you a
little practice in using records, try to
write a routine that would allow you to
enter the data for this program. You can
have the user input the high and low
temperatures, and the computer calculating
the amount of change in high temperature
from the previous day. When you have that
routine working, write a program to keep
track of the time of the sun rising and
setting each day. Also keep track of how
many hours of daylight there are in each
day and the change in daylight hours from
one day to the next. The more practice
you get, the better you become.
Records are a very useful tool. As will
be shown next month, they can be used to
provide an easy means of working with data
objects (the manual calls them 'virtual
records'), we're going to call them worms!
|19. An Object Lesson||February 1996|
INT xx=$E0, yy=$E2 ;DIR parameters
TYPE worm = [BYTE X1,X2,X3,X4,
INT DX, DY]
DEFINE COUNT="80" ;1 - 99 MAX WORMS
DEFINE SPEED="250" ;0 - 255
worm POINTER wm
BYTE ARRAY memory(1200),
mask=[$7F $BF $DF $EF
$F7 $FB $FD $FE]
CARD ARRAY screen(96) ;PLOP/FIND table
; ( Clip and Save!)
PROC PLOP(BYTE PX,PY) ;Faster PLOT
BYTE ARRAY ROW ;command
ROW=screen(PY) XB=PX RSH 3
XV=PX &7 PM=COLOR LSH (7-XV)
ROW(XB)=(ROW(XB)& mask(XV)) % PM
BYTE FUNC FIND(BYTE PX,PY)
BYTE ARRAY ROW ;Faster LOCATE
BYTE XB,XV,PM ;command
ROW=screen(PY) XB=PX RSH 3
XV=PX & 7 PM=mask(XV)!255
IF R<20 THEN yy=1
ELSEIF R<60 THEN xx=1
ELSEIF R>175 THEN xx=-1
ELSEIF R>225 THEN yy=-l
;---------Clip this too-----------
GRAPHICS(6+16) ;160 x 96, 1 color
screen(0)=SCRMEM ;Setup array for
FOR I=1 TO 95 ;PLOP and FIND
DO screen(I)=screen(I-1)+20 OD
FOR I=0 TO COUNT ;Random placement
DO ;of worms
wm X2=wm.X1 wm.X3=wm.X1 wm.X4=wm.X1
wm.Y2=wm.Y1 wm.Y3=wm.Y1 wm.Y4=wm.Y1
PICK_DIR() wm.DX=xx wm.DY=yy
FOR I=0 TO COUNT
wm.X4=wm.X3 wm.X3=wm.X2 wm.X2=wm.X1
wm.Y4=wm.Y3 wm.Y3=wm.Y2 wm.Y2=wm.Y1
IF Z=0 THEN ;OK to move
IF R<240 THEN ;Do move
ELSE ;Change direction
FOR J=0 TO 3
THEN EXIT FI
ELSE ;Not OK to move
FOR J=0 TO 7 ;Find new direction
THEN EXIT FI
PROC WAIT() ;Slow down display
DO J==-1 OD
As stated at the start of this monthly column, I
intended to give you routines you can use, and a
little insight into programming with ACTION!.
This issue gives you new PLOT and LOCATE
routines that are faster than those supplied
with ACTION!. In addition to the clip and save
section, part of the START_UP routine must be
included to initialize the screen array. You
may remember it is faster for the computer to
look up data in a table than it is to calculate
the needed values every time. This is what the
array does in the PLOP and FIND procedures.
|20. Number Twenty!||February 1996|
Last months program should have revealed
the cookie-cutter approach by using an
array of records. Each worm had 4 pixel
segments and its own direction of travel
stored in a record. The MOVE procedure
handled all the worms in the same manner,
which eased the programming task. This
same method can be used for other programs
where you have many identical, or nearly
identical, objects. Some examples might
include soldiers engaged in a war, rooms
of a haunted castle, employee files, days
in a calendar, and many, many more.
Although you cant directly declare a BYTE
array in a record, you can coax ACTION! to
store arrays in records. This month you
will see how you use and access a record
that has a BYTE array in it. The program
asks you to enter three student names,
with three test scores each. It then
displays the student name and average of
the test scores, along with their grade.
At the bottom of the display, the records
themselves are shown, with spaces inserted
between the name, test scores, average,
and grade. This section shows you how the
record would look (minus the spaces) if it
were stored in a disk file.
TYPE CLASS=[BYTE namlen
CLASS POINTER student
BYTE ARRAY memory(l00)
BYTE ARRAY prompt= "Enter test score "
PrintE("Enter NAME of student;")
IF student.namlen>10 THEN
PrintF("%S 1; ",prompt)
PrintF("%S 2; ",prompt)
PrintF("%S 3; ",prompt)
IF av>=92 THEN student.grade='A
ELSEIF av>=84 THEN student.grade='B
ELSEIF av>=76 THEN student.grade='C
ELSEIF av>=68 THEN student.grade='D
BYTE POINTER ptr
student=memory ;Locate storage space
FOR i=l to 3
PRINTF("Student number %U%E",i)
PutE() x=2 y=2
PrintE("NAME AVG GRADE")
FOR i=1 TO 3
ptr=memory ;Show records
FOR i=1 TO 3
FOR j=0 to 15
y=18+i x=2+j ;Insert spaces
IF x>12 THEN x==+2 ;Tests
IF x>17 THEN x==+l ;Avg
IF x>19 THEN x==+l;Grade
This program runs funny, in that whenever
the name is less than 10 characters long,
the records still hold old data behind
the student name. See if you can fix
this problem. To see this effect, run the
program and enter AAAAAAAAAA for the first
name, then run it again and enter Z for
the first name. You will see that part
of the name AAAAAAAAAA is still in memory.
|21. Final Episode...||March 1996|
Up to now I have discussed the different
aspects of a program for the computer.
Now its time to discuss how to turn those
programs in the computer, to files on the
disk for everyone to enjoy.
After you have typed in a program, you
are required to enter the Monitor to com-
pile and run the program. The Monitor will
also save the compiled code to disk. The
file produced from the Monitors write
command (W "D1:MYPROG.EXE") is executable
from the disk. After you have written a
program file to the disk from the Monitor,
you can then call up DOS and run the file
from the command line prompt. If you have
supplied all of the necessary code for
execution, you will be able to run the
file even without the ACTION! cartridge
installed. Those files are the type of
files you can send to your friends, who
may not have the ACTION! cartridge. For
a discussion on how to get programs to run
without the cartridge, refer back to my
The DOS file system has a method of
determining what type of file is stored
on the disk. By using the first two bytes
in a file, it can determine if the file
was meant for direct execution, or for
use with the BASIC cartridge, and so on.
If the file begins with two 0's, it is
probably an executable file, BASIC uses
255, 255 for its tolkenized form. The
next four bytes in the file tell DOS where
to put the stored data in memory, and how
much to put there. By using the two CARD
values as the start and stop memory
addresses of the code segment, it can load
the executable code anywhere in memory.
The Monitor supplies all these bytes for
you when you use the write command. DOS
also allows for the appending of files, so
that some code may be loaded in at one
address, and other code may be loaded in
elsewhere. When the computer has loaded
data into the last (stop) address, DOS
checks to see if there is more data in the
file. If it finds more, it checks to see
if the next two bytes are 0,0 (which does
happen when files are appended). If not
and there is still more data in the file,
DOS will assume the next four bytes are
the start and stop addresses of another
segment of code (or data, depending upon
who put what, where!) This process will
repeat until there is no more data in
The ATARI operating system also has two
special addresses for use in handling the
executable files. These addresses are
RUNAD (Run Address = 736, 737) and INITAD
(Init Address = 738, 739). When data is
loadied into INITAD, the ATARI Operating
System (OS) interrupts the load process and
begins executing code at the address
pointed to by INITAD. When that code has
finished (via a RETURN statement), the
loading process resumes. When data is
loaded into RUNAD, the loading process is
allowed to complete, then execution of
code begins at the address pointed to by
RUNAD. You might now see how professional
programmers put a little title screen up
while their program is loading. A short
program to put text on the screen could be
loaded in, the INITAD could be used to
run that code, then loading of the main
program could proceed. Using ACTION! it
is real easy to do things like this. When
the Monitor writes a program to the disk,
it also includes a short segment to load
INITAD with the starting address of the
main procedure. Appending files written
by the Monitor will always act in the
manner stated above, some part loads and
runs, then another loads and runs, and
another, and another, as many times as
there were files appended together. Try
it yourself, and put it to good use!
With all the routines and tips I have let
you in on, you are now ready to undertake
your own projects with confidence. With
just a little advanced planning, almost
anything a computer can do, can be done
using the ATARI. It is up to you, the
user of the computer, to put the computer
to use. It doesnt do any work sitting on
a shelf. You dont have to rely on some
distant programmer to write the program
you want to use, you can write it your
self. It seems the younger generations
pick up the new technology quicker than
old folks, which is all the more reason
to introduce young kids to the ATARI
computer. It is easy to use, and simple
to program, providing a stepping stone to
the larger machines for those kids who may
want to pursue a career involving some
aspect of programming a computer. The
bulk of computer programming is done by
those who have a need. The limits of
what a computer can do is bound up only by
the imagination of those people willing
to attempt the programming of their
computer. My advice; reach for the stars!
It has come time to close this column and
move on. I want to thank Mike Schmidt our
newsletter editor for the great job he has
done organizing, printing, and mailing our
club newsletter to all our members. All
the people in the club who volunteer their
time to help SPACE provide support for the
ATARI community, deserve a hearty thanks.
Its the members, who support SPACE through
membership and the purchase of DOMs, that
are to be congratulated on keeping this
group together for so long. Nice going.
This is my last submission, I had a fun
time, I hope you gained a little more
confidence in your own efforts.