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Article #98 (214 is last):
From: xx004@cleveland.Freenet.Edu (Atari SIG)
Newsgroups: freenet.sci.comp.atari.product.8bit.zmag
Subject: Z*Magazine: 29-Feb-88 #95
Reply-To: xx004@cleveland.Freenet.Edu (Atari SIG)
Date: Sat Jul 24 09:22:18 1993


______________________________________
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|//\SYNDICATE ZMAGAZINE  ISSUE #95\//|
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|//\|PUBLISHER/EDITOR: RON KOVACS|\//|
|//\|ASST. PUBLISHER:KEN KIRCHNER|\//|
|//\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\//|
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|____________________________________|
|February 29, 1988                   |
|____________________________________|
|This Issue Dedicated to my wife,    |
|daughter and new son!               |
|____________________________________|
|Syndicate Publications              |
|Post Office Box 74                  |
|Middlesex, New Jersey 08846-0074    |
|____________________________________|
|BBS (201) 968-8148  300/1200 24 hrs |
|____________________________________|
|Contents                            |
|____________________________________|
|*|A New Arrival!!                   |
|*|Systems Prgm'g on the Atari XL/XE |
|*|What's New On CompuServe Atari    |
|*|Atari News Update                 |
|*|Atari Basic Programming Part 8    |
|*|Modem Noise Killer                |
|____________________________________|
 A New Arrival!!
______________________________________
Earlier today at 1:46pm Adam Michael
Kovacs was born!  Mother and baby are
doing fine.  Guess the child knew we
has an issue to get out! We are now a
thriving family of four and appreciate
the well wishes sent in over the last
few weeks.  It has been a long 9 
months, we are happy and hope you are
too, in hearing the news!!
______________________________________
SYSTEMS PROGRAMMING ON THE ATARI XL/XE
______________________________________
PART 1

COPYRIGHT (C) 1988 BY TOM HUNT

NOTICE: This article may be
republished, in portions or in it's
entirety, if credit to the author is
given.

There is no doubt in my mind that the
subject of this article is very broad.
But, we will try and focus in on the
systems environment aspect of this
topic. More precisely, we will be
examining the steps and considerations
I found necessary to produce a
multitasking environment (called MTOS)
for our beloved 8-bit Atari computers.
This may help others in extending "the
frontier" of what we can do with our
machines.

MTOS is licensed to:
      DATAQUE
      3308 PARK AVE. W.
      P.O.BOX 134
      ONTARIO, OH 44862

Let's start by looking at the very
heart of the system, the central
processing unit (CPU). The CPU in our
computers is the 6502C. It is driven
at a clock speed of 1.79 MHz. It has
8-bit registers, and a 16-bit address
bus. While it is a very able CPU, it
has some very limiting constrictions
when compared to more capable
microprocessors. The Motorola 68000
processor has around 70,000
transistors on the chip, an 8 bit CPU
(like the Intel 8085) has around 5,000
transistors. The 16-bit and 32-bit
CPU's are faster, have expanded
address space, and sometimes have
better instruction sets. This does not
mean that we should stop exploring the
limits of our Atari XL/XE computers.

On the contrary. What we must first do
is accurately evaluate what our true
limitations are. Frequently we will
find that it is not so much the CPU
that is the limiting factor. It is our
minds, and in our imaginations. It is
in the way we perceive a problem, and
how we go about solving it. (Truly, a
Guru Meditation!)

Whereas the newer CPU's have address
space in the megabyte range, our
machines are confined to 64k. The way
to extend this range is through bank
switching. Some 8-bit Atarians are
using memory in the megabyte range
through this method. If you own an XL
computer with only 64k, then I suggest
you upgrade your memory to at least
256k. There are kits available to do
this yourself, or by a qualified
technician. Also, there are user's
groups across the country that are
waiting to help, if you need it. The
rest of this article assumes that we
have at least 128k in which to use.

After doing what we can to extend the
memory capabilities of our machines,
we consider the clock rate of our CPU.
1.79 MHz is pretty slow to start with.
Some Atarians have experimented with
installing faster clock crystals to
speed up the CPU. But what they have
found is that it throws the video off.
It messes up the display. Perhaps with
the advent of the 80 column box from
Atari, the hardware hackers will have
better luck with this endeavor since
the box apparently bypasses the ANTIC
chip. Since there is nothing we can do
about the speed (for now), we will
have to come up with optimizing
techniques for time sensitive areas.
This is where we must begin looking
for new ways to do things. The
limiting factor is on us.

I personally do not feel that the
instruction set of our CPU is a
limiting factor. Many of the newest
CPU's employ RISC architecture. RISC
stands for reduced instruction set
computer. It seems that there are only
a few instructions that do 90% of the
work. A couple of instructions we
defiantly could use would be 16-bit
multiply and divide. Perhaps these
instructions are found in the new
65816 CPU. The people at Western
Design Centers claim that it is
pin-compatible with the 6502C. Rumors
abound of people working on a XE/GS
that employs this chip. But in the
meantime, we have more than enough
opcodes to do some serious work.

The next part in this series will be
USING THE INTERRUPT SYSTEM. The
programming of interrupt handlers is a
considerable part of practical systems
programming.
______________________________________
Whats New On CompuServe
______________________________________
      THE ATARI USERS NETWORK
            (SIG*ATARI)

WHAT'S NEW IN SIG*ATARI   (Feb. 16)

NEW FORUM SOFTWARE

A new version of the Forum Software
was installed in all three Atari
Forums. Most changes are internal,
however, there are some changes to the
USER OPTIONS area (OP) of the Forum. 
Please see FORUM.235 in DL 0 of the
ATARI 8-Bit or 16-Bit Forum for
details!

** The ATARI 16-Bit Forum **
(GO ATARI16)

The newest edition of ST-REPORT #21 is
now available in DL 8. If you haven't
been reading the monthly editions of
this EXCELLENT Atari-oriented
newsletter, we urge you to take a look
at the latest copies.  Nice job, Ron
Kovacs!

** ATARI Programmers & Developers **
(GO ATARIDEV)

ATTENTION ALL DEVELOPERS!

We will be assembling a list of
developer names and User IDs of those
parties who regularly frequent the
ATARI Forums for an upcoming
publication.  If you do NOT wish your
name and PPN to be included in this
published list (or to make sure that
you ARE included in this listing),
please contact SYSOP*Ron Luks
76703,254 and express your desires.
______________________________________
Atari News Update
______________________________________
ATARI TO UNVEIL UNIX-LIKE SYSTEM

Look for Atari Corp. to use the stage
of next month's Hanover Computer Fair
in West Germany for the coming-out
party of its new low-cost Unix-like,
68030-based workstations.

Computergram International newsletter
reports that the workstation is based
on Whitesmiths' Idris system which
Atari licensed last year. In addition,
the newsletter reports it hears that
Atari also will introduce a desktop
publishing system for under $5,000,
"getting close to the price of a good
laser printer alone."

The publication says the system will
be composed of the Mega computer, the
SLM804 laser printer and Atari Deskset
software. "The software is claimed to
put true WYSIWYG (what you see is what
you get) on the screen," CI says, "and
page formatting will be handled inside
the computer rather than on the
printer, 1 meg of memory being
dedicated to laser printer commands."

Computergram International is a
regular feature of NewsNet.
______________________________________
Xx LEARNING TO PROGRAM IN ATARI BASIC
 ...Part 8 of a continuing series...
______________________________________

------------------------------------
COUNTERS:
------------------------------------
Often, we wish to keep track of how
many times we have gone through a
loop. We may want to do something
every other trip through, or count
when to end, or keep track of how many
times we've done a thing.  This is
done with COUNTERS, which are +1 or
adding statements placed within the
body of the loop. These let the
computer do the counting, freeing us
from this chore, which is the whole
idea behind using and programming
computers.

These often look like:

10 X = X + 1

70 TOTAL = TOTAL - 5

25 COUNT = COUNT + 1

Note the way these are coded. Counters
say, "a variable equals itself plus
something". The variable name appears
on each side of the equal sign, with
the "plus something" on the right.
Remember a LET statement takes what's
on the right of the equal sign, and
assigns it to what's on the left of
the equal sign. It's a little hard to
think so elementary at first, X = X +
1, but becomes second nature soon. I'm
serious, they're hard to catch on to
coding.
------------------------------------
SUMMERS:
------------------------------------
SUMMER is not a proper programming
term, but that's what I call these.
Summer's are utilities much like
counters, but rather than counting,
they total or add together or
accumulate a running sum total number.
For example, a summer in a payroll
program  keeps track of how much we
have earned to date in the year.

These are coded much like counters,
but often have a variable for a "plus
something" on the right hand side.
Some examples:

15 TOTHOURS = TOTHOURS + HOURS

10 YTDSAL = YTDSAL + WEEKSAL

55 SUM = SUM + (14.7*TAX-INTEREST)

10 TOTAL = TOTAL + ADDON

If counters usually tell us "how many"
a thing is now, then summers keep
track of "how much" we have now. Trust
me! This will make sense someday.
Sometimes when a program you are
writing is acting up, and you can't
figure it out, you can install some
counters and/or summers in the code,
and RUN it. Break in with the BREAK
key, and ask it to print the value of
a counter or summer in immediate mode
at the READY prompt, like "? SUMM" or
"? TOTAL" or "? COUNT". It may be
helpful to see if it's looped more or
less times than you had thought, or
perhaps you find it got stuck after a
set number of loops. When the
program's debugged, take out the lines.
------------------------------------
Putting It All Together
------------------------------------
Let's write a program that puts this
all together, that you can continue to
work on and develop, and learn on.
Let's imagine you are a teacher, who
needs to average student grades for
the entire semester, and assign a
letter grade.  If doing this by hand,
we would add all of a student's
grades, divide by the number of
grades, and find a numerical average.
This would then be compared to a range
of numerical grades and letter grades.
We must count the number of grades
each student has, to find the correct
number to divide by. This if often
confusing when students have a
different number of grades in a class,
and could lead to an error.

Let's write a program that calculates
these grades on our Atari computer in
BASIC. When calculating the average,
it must keep track of how many grades
we enter for each student,
automatically choosing the correct
divisor. The program should prompt you
for correct input, and error check it
for correctness. It should stop taking
grades and display the average when we
type in a grade of 999 to signal the
end of input.

We may add to this program at some
point, so we'll start numbering it at
1000. Leaves lots of room "below."

1000 REM **   EZ-GRADE   **
1010 REM JACKSON B    6/87
1020 REM
1030 REM CLEAR,INITIALIZE,PROMPT,IN
1040 ? CHR$(125):TOTAL = 0:COUNT = 0
1050 ? :? :? "Enter grade  ";
1060 INPUT GRADE
1070 REM
1080 REM TEST,INCREMENT,SUM,LOOP 
1090 IF GRADE = 999 THEN 1160
1100 IF GRADE <0 OR GRADE > 100 THEN
GOTO 1050
1110 TOTAL = TOTAL + GRADE
1120 COUNT = COUNT + 1
1130 GOTO 1050
1140 REM 
1150 REM AVERAGE AND OUTPUT
1160 AVG = TOTAL / COUNT
1170 ? :? "The AVERAGE for these ";
COUNT;" grades is ";AVG
1180 ? :? "(Press 9 to enter more
grades)  ";
1190 INPUT M
1200 IF M = 9 THEN 1040
1210 END

This program uses a counter (COUNT) to
keep track of the number of grades
entered, and a summer (TOTAL) to keep
a running total.  Entering a 9 after
an average, will continue the program.
Any other key will end the program.

Note that the counter and summer are
initialized (set to zero) OUTSIDE the
main loop.
------------------------------------
Sample Problems:
------------------------------------
PROBLEM 4

Add lines to EZ-GRADE to determine a
letter grade A, B, C, etc, in
additional to a numerical average.
(HINT - add a pile of IF-THEN's after
line 1170 that test whether input is
between 70 and 79, 80 and 89 etc, and
assign a letter to a variable. Use a
one character string variable to hold
the letter grade, that is dimensioned
outside the loop (line 1135.)
------------------------------------
PROBLEM 4A

Modify  EZ-GRADE so that instead of
typing in 999 to signal the end of
data, you simply press RETURN without
having entered a grade (a NULL entry.)
Have it prompt whether you really want
to stop entering data before it
calculates the average and letter
grade. (HINT - you need a string
variable to bring in a plain carriage
return. The VAL function will
translate your string input into a
number.)

The way you test for an empty carriage
return (RETURN) is to test the input
for equality with two sets of
quotation marks back-to-back with
nothing between them as:

195 IF NAME$ = "" THEN 255

This tests True for a null input, and
goes to line 255.  You MUST hit the
RETURN key to pass an INPUT statement
in BASIC.
------------------------------------
PROBLEM 4B

Write a GUESS THE SECRET NUMBER
program. Use the following line early
in the program, which will generate a
random number between 1 and 100, and
assign it to the variable SNUM. Write
your program to prompt the player for
a number from 1 to 100, and give
feedback if the guess is higher,
lower, or equal to the secret number
(a winner.) Write it to loop 10 times,
then signal that the 10 guesses are
up, and you lose!

35 SNUM = INT(RND(0)*100+1)
------------------------------------
PROBLEM 4C

Write a program that asks you to guess
the capitol of 5 states, and gives you
a grade from 0 to 100 on your answers.
------------------------------------
This concludes Part 7 Lesson 4 of
Learning to Program in Atari BASIC.

Let's back up for one moment, and
recall a rap we had in Lesson 1, in
which I identified 3 tasks beginners
face in learning to program.

1. Learning to operate the hardware.
2. Learning to program.
3. Learning the BASIC language.

Once you learn most of the basic
programming concepts and structures,
you will never need to learn them over
again, if you pursue other languages.
For instance, you will not relearn the
concepts of testing, branching and
counters. You will simply ask "What's
the syntax to...test, loop, branch,
etc." It is natural to be very
confused right now. Do not quit
because you are confused. That simply
means your brain is making the correct
thinking adjustments. It is natural to
dream about programs and problems when
working on new projects. Relax, it's
not permanent, and some of your best
ideas just pop into your head after
days of muddled thoughts.
------------------------------------
Contact me at:
Jackson Beebe
Prairie Data Fields
807 W. Hill Street
Urbana, IL 61801
______________________________________
Modem Noise Killer
______________________________________
With this circuit diagram, some basic
tools including a soldering iron, and
four or five components from Radio
Shack, you should be able to cut the
noise/garbage that appears on your
computer's screen.

I started this project out of
frustration at using a US Robotics
2400 baud modem and getting a fare
amount of junk when connecting at that
speed. Knowing that capacitors make
good noise filters, I threw this
together.

This is very easy to build, however
conditions may be different due to
modem type, amount of line noise, old
or new switching equipment (Bell's
equipment), and on and on. So it may
not work as well for you in every
case. If it does work, or if you've
managed to tweek it to your computer/
modem setup I'd like to hear from you.

I'd also appreciate any of you
electronic wizzards out there wanting
to offer any improvements. Let's make
this work for everyone!

Please read this entire message and
see if you understand it before you
begin.

OK, what you'll need from Radio Shack:

1 #279-374 Modular line cord if you
   don't already have one. You won't
   need one if your phone has a
   modular plug in its base $4.95

1 #279-420 Modular surface mount jack
  (4 or 6 conductor) $4.49

1 #271-1720 Potentiometer. This is a
  5k audio taper variable resistor.
  $1.09

1 #272-1055 Capacitor. Any non-
  polarized 1.0 to 1.5 uf cap should
  do. Paper, Mylar, or metal film caps
  should be used, although #272-996
  may work as well. (272-996 is a
  non-polarized electrolytic cap)
  $.79

1 100 ohm resistor - quarter or half
  watt. $.19

1 #279-357 Y-type or duplex modular
  connector. Don't buy this until
  you've read the section on
  connecting the Noise Killer below.
  (A, B,or C) $4.95

First off, open the modular block. You
normally just pry them open with a
screwdriver. Inside you'll find up to
6 wires. Very carefully cut out all
but the green and red wires. The ones
you'll be removing should be black,
yellow, white, and blue. These wires
won't be needed and may be in the way.
So cut them as close to where they
enter the plug as possible. The other
end of these wires have a spade lug
connector that is screwed into the
plastic. Unscrew and remove that end
of the wires as well. Now, you should
have two wires left. Green and red.

Solder one end of the capacitor to the
green wire. Solder the other end of
the capacitor to the center lug of the
potentiometer (there are three lugs on
this critter). Solder one end of the
resistor to the red wire. You may want
to shorten the leads of the resistor
first. Solder the other end of the
resistor to either one of the
remaining outside lugs of the
potentiometer. Doesn't matter which.

Now to wrap it up, make a hole in the
lid of the mod block to stick the
shaft of the potentiometer through.
Don't make this hole dead center as
the other parts may not fit into the
body of the mod block if you do. See
how things will fit in order to find
where the hole will go.

Well, now that you've got it built
you'll need to test it. First twist
the shaft on the potentiometer until
it stops. You won't know which way to
turn it until later. It doesn't matter
which way now. You also need to
determine where to plug the Noise
Killer onto the telephone line. It can
be done by one of several ways:

A. If your modem has two modular plugs
   in back, connect the Noise Killer
   into one of them using a line cord.
   (a line cord is a straight cord
   that connects a phone to the wall
   outlet. Usually silver in color)

B. If your phone is modular, you can
   unplug the cord from the back of it
   after you're on-line and plug the
   cord into the Noise Killer.

C. You may have to buy a Y-type
   modular adaptor. Plug the adaptor
   into a wall outlet, plug the modem
   into one side and the Noise Killer
   into the other. Call a BBS that has
   known noise problems. After you've
   connected and garbage begins to
   appear, plug the Noise Killer into
   the phone line as described above.
   If you have turned the shaft on the
   potentiometer the wrong way you'll
   find out now.

You may get a lot of garbage or even
disconnected. If this happens, turn
the shaft the other way until it stops
and try again. If you don't notice
much difference when you plug the
Noise Killer in, that may be a good
sign. Type in a few commands and look
for garbage characters on the screen.
If there still is, turn the shaft
slowly until most of it is gone. If
nothing seems to happen at all, turn
the shaft slowly from one side to the
other. You should get plenty of
garbage or disconnected at some point.
If you don't, reread this message to
make sure you've connected it right.
______________________________________
Final Word
______________________________________
This issue was intended to be a bit
longer than it is, But due to the rush
of current events, I removed a few
scheduled items till next week.

We are also in a development stage 
with a few projects. If you want to
get involved with them and are a
ZMag BBS carrier, give us a call on 
the BBS and join the discussion!

Happy Leap Year!
______________________________________
Syndicate ZMagazine  February 29, 1988
Issue #95. (c)1988 SPC/Ron Kovacs
______________________________________




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