May June 1980 - Commodore Computers

MAY/JUNE.1980 MAV/JUNE. 198O ISSUE.a 4
COMPUTE. 89
FOT For)'OIiT your cOl/lienie1lU: convenience i,l in making flU usr f!.f of the following fol/owillg (lTlide. article, I I'm '/'r lrprilltrd reprinted (I a
/JlJrtioll portion oj of C~/lck Chuck.I0/I/ Johnson HOIl 's rxu:lIrnl excellent article ankle ill in Jjesl lies! of the PET
Ga:etlr, Gazette, p. pA2. -I2, RCL
PET ting WITH
PET ting WITH
AJOYSTICK
HONey B. Herm on
Harvey B. Herman
Chemistry Deportment
Department
University of North Carolina
at Greensboro
Greensboro, N.C, 27412
Greensboro, N.C 27412
My y older style PET keyboard gets banged around
quite a bit when my kids play games which use the
number pad. , A recent PET-Pourri column in Kilobaud
((1) I) prompted me to install a joystick on my
PET in order to save my keylOps keytops from further wear.
This article is intended to share my experiences
with this project and lO to encourage other fumblethumbs
like myself to try it. .
fumble-
I purchased the Atari-joysticks from Sears as
suggested in the above column (catalog #6C99835)
for r $9.95 each. Since I could not find a mating
connector, eClOr, I cut off ff' each end and attached ached them to a
User Pon Port connector as per the e instructions (see also
refs 2 and 3). The latter connector can be purchased
from any number of companies (e.g.,, AB All Computers).
Four signal d iodes ( I N662), whose speci fi ca­
puters). Four signal diodes (1N662), whose specifica
tions I believe are not t critical, ical, are also used in this
s
super simple interface circuit it which can be constructed
in about 112 1/2 hour. Check to make sure thatt the
diode cathodes are connected as shown in the e circuit
diagram (1) I) and the color coded wires of the joystick
are connected to the proper pins s ofo f the e User Port
conneclOr. connector. OtherwiseO no special precautions are arc
necessary. I did it right the first time e (yes brag!) brag')
This neat hardware would, , of course, be useless
withoutw software to work it. CursorC magazine e (4)
has supplied several programs which have a joystick
option. I tried these first (Demon, Canyon, Pickup
and Nab) with happy success. . These programs area rc
written to work withw various model joysticks wired \"ired and
oriented in differentd llt ways. SinceS my configuration
io n
was fixed I modified the joystick subroutine uti in each
Cursor program to lO skip the test step. That procedure
can be tedious if a program is run repeatedly. TheT following g changes in the CursorC joystick subroutine
should work for alla Atari-type type joysticks wired according
to the circuit diagram in reference 1: I:
610306 PRINT: FOR R I = ~ 0 to 5: READ T, T , P:
GOSUB 61120: 6 T(I) T = ~ T: T : J(T) J ) = ~ P: NEXT I
611206 T = ~ INT (T/16) I16) ANDA NDT: RETURNR U R N
612506 DATA 255, 5, 223,4,239,6 239, 6 127,8, 191,2,
1,2,
63, 0.7, 0 1, I , 9, 3
I ran the original program once to find the
values in the T array and used data statements tement s in the
modified program in order to skip the test step. This
considerably speeds up thee beginning of a game. I
have deliberately ignored thee rationall behind the bitt
manipulations ns in statement 61120. 20, It is not necessary
to understand that in order to use joysticks. I emphasize
this point because I hope it will encourage
PET users who may strain aatl bitss to attempt projects
such as described here. I Inn a future an article e I
may try my hand at a tutorialo forr those who wish
to delve imo into thiss mystery further. er,
If a program was nott writlen written with a joystick
in mind another modification n procedure must be used
to convert it a\",ay away from number pad usc. use. As an
example I modified the programm Obsracl Obstacle e (5) which
utilizes utlitzes the full keyboard as two pseudo-joysticks.
Each player manipulates hiss piece (screen character)
with the now standard keyboard patterns, ""W, , X X, , A
and D" and "8, 2, 4, 6". The object is to keep from
running into the screen traill left by the other
player - the first to do so loses. As withh many games it
is easier to use than to describe. The following
statements in the original program are used lO to sense a
keypress by a player and change direction if necessary:
260 GET R$
265 IF RS R$ = ~ ""W" W " THEN AD = ~ 1I
•
300 IF RS ~ "8" THEN E 11D llD = 1
•
It If W is pressed the direction of the player on the
leit's left's piece is changed to up. If 8 is pressed
the direction of the player on the right's piece picce is
also changed to up. . Player and direction are detc deterr­
mined by the above keyboard pattern which can be
learned quickly by new pl ayers.
learned quickly by new players.
Converting a program like this s to joystick use is
very easy. The following owing statements s will do this:
260 M = ~ PEEK (59471)
1)
265 IF (M ORO R 240) = ~ 247 THEN AD = ~ 1I
•
300 IF (M OR 15)
127 THEN E BD =
•
The elipsis is can be fleshed out with the help of
the table below. . A peek ata t the User Port Pon gives a
unique value e for each position on of o f the e joystick as long
as only y one is being used. . It is necessary to "mask"" with 15 IS or 240 if the possibility ilit y exists of both
being g used at the e same time. If only one joystick
is used and it doesn't matter which, a further opera-