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Message started by ggn on 12.08.11 at 08:43:00

Title: The Atari Enhanced Joystick Ports FAQ 0.90
Post by ggn on 12.08.11 at 08:43:00

Code (]            The Atari Enhanced Joystick Ports

              Frequently Asked Questions

           Version 0.90 - 24th September 1996



     1.1      About the author
     1.2      Other contributors
     1.3      New in this release/history
     1.4      Disclaimer
     1.5      The symbols used in this FAQ
     1.6      Construction tips
     2.1      What is an enhanced joystick port (EJP)?
     2.2      What machines have them?
     2.3      What about other machines?
     2.4      What is the pinout of an EJP?
     2.5      What can they be used for?
     3.1      Jaguar joypads
     3.2      So how does a joypad work?
     3.3      Example joypad code
     3.4      Joypad circuit diagram
     3.5      Using joypads as normal joysticks
     3.6      Joypad -> joystick adaptor circuit diagram
     3.7      Programs which use joypads
     4.1      Jaguar team tap
     4.2      Example team tap code
     4.3      Team tap circuit diagram
     4.4      Programs which can use a team tap
     5.1      Using joysticks with an EJP
     5.2      Example joystick code
     5.3      Joystick -> EJP adaptor circuit diagram
     6.1      Analogue joysticks
     6.2      Example analogue joystick code
     6.3      Analogue joystick circuit diagram
     6.4      Programs which will use an anlogue joystick
     7.1      Digital paddles
     7.2      Example digital paddle code
     7.3      Digital paddle circuit diagram
     7.4      Programs which will use a digital paddle
     8.1      Analogue paddles
     8.2      Example analogue paddle code
     8.3      Analogue paddle circuit diagram
     8.4      Programs which will use an analogue paddle
     9.1      Light pens
     9.2      Example light pen code
     9.3      Light pen circuit diagram
     9.4      Programs which will use a light pen
     10.1      Other output devices
     11.1      Other input devices
A '*' before an item indicates that it has been added or updated with
this release of the FAQ.

1.1About the author
My name is Xav, and I have been using Ataris for several years now.
I began writing this FAQ because I was becoming fed up with seeing
the potential of the enhanced joystick ports (EJP) going to waste
due to a lack of understanding or information on how to program for

As most people will know, any game (or other application) is only as
good as its interface, and not every game is best suited to a mouse
or joystick. Over the years a number of companies, not least of
which is Atari, have pioneered the use of a wide range of different
devices, ranging from steering wheels to guns, and everything in
between. I hope that this FAQ will enable people to easily build a
selection of different controllers, and more importantly that it
will help programmers use them.

If you have any useful information regarding the EJPs, or if you
feel there are any omissions or errors in this FAQ (I know I'm not
perfect), please feel free to contact me at the address shown below.
Similarly, if you have written, or know of any programs that use the
EJPs effectively, please let me know, so that I can include their
details here.

All of this work is copyright, and whilst you are free to use and
distribute this information, certain restrictions apply:-

     1)      No profit should be made from the distribution of this
           FAQ, apart from any minor amounts for PD libraries.

     2)      This FAQ may not be distributed on a magazine
           coverdisk, or disk based magazine without my prior
           consent. In most cases this will be given, though
           there may be a small surcharge to commercial

     3)      This FAQ may not be used as the basis for a magazine
           article in its own right. If you wish to publish an
           article based on this FAQ, please contact me, and I
           shall be happy to write it for you (for a small
           charge, of course) or discuss payment.

     4)      If you pass this FAQ on to anybody else, it must be
           unchanged, and untampered with. In particular, my
           contact details must remain intact, in case the
           recipient wishes to receive the latest version.

For the duration of this version of the FAQ, I can be contacted as

Email (preferable):      mbge4mdc@fs1.ee.man.ac.uk

Snail mail:            Xav,
                 2 Beech Green,
                 HP21 8JG

If you wish to obtain the latest version of this FAQ, please, if you
possibly can, get it from my web pages:-


If you are unable to do this, you can request a copy from me via
email, although it may take me some time to get round to it. If you
genuinely have no net access, and are unable to get this FAQ from a
friend or PD library, then snail mail me sending a BLANK FORMATTED
your request will be ignored. Sorry to be so harsh, but I do not
have the time or money to chase everyone up.

If you are sending information to add to this FAQ, either snail mail
or email are acceptable, at your discretion.

I am also always grateful for any money or other gifts. Whilst I am
not so tight as to make this FAQ "shareware", I would like you to bear
in mind the amount of time, effort and money that has gone into
obtaining the data in this FAQ. I can assure you, also, that any money
sent to me will be spent on components for further research and
information, which will then be added to this FAQ.

1.2      Other contributors

Anthony Jacques  has kindly filled in a lot of
spaces that I left for games supporting the EJPs. He has also been
kind enough to let me butcher his PC analogue joystick - although this
was mainly to see if I could get it to work with Moonspeeder for him

1.3      New in this release


This version has been rushed out because a large number of people were
asking for some of the information it contains. Whilst it is by no
means complete, I hope that it will be of use until the full version
(1.00) is released.

Please still mail me with any additions, since I'm sure I haven't
thought of _everything_, even with my plans for V1.00

1.4      Disclaimer

To the best of my knowledge the information in this document is
correct. Neither I, nor any other contributors, can be held
responsible for any loss or damage that may occur as a result of the
use, or misuse of any of the information in this FAQ. In particular,
this FAQ describes a number of hardware devices that can be
manufactured by individuals - as with all such projects it is
possible to damage your computer if these devices are incorrect. No
responsibility can be accepted for such damage, or its consequences,
whether or not the information supplied was at fault.

Any and all trademarks used herein are the property of their owners,
and no official connection is implied or claimed between them and

1.5      The symbols used in this FAQ

A large proportion of this FAQ is dedicated to sharing knowledge about
the various alternative controllers available for the EJPs. This takes
two main forms - firstly there is (wherever possible) source code to
give examples to programmers in the hope that they will be more
willing to use the EJPs. Secondly there are circuit diagrams to
enable anyone with the right skill and knowledge to build a range of
alternative controllers for themselves.

Owing to the fact that this FAQ is in purely ASCII format, to make it
as simple as possible to spread to other people, the circuit diagrams
are difficult to show. Consequently the following conventions will be

     --------- or  |         = Interconnecting lines

              |    |
     --*--  --*--  *--  = Connection of three or more conductors
          |      |    |

     ----+   |
         |   |          = Interconnecting lines
         |   +-------
         |        |
     ----|---  -------  = Conductors crossing but not joining
         |        |
         O     ----O
         |              = Pin or terminal (e.g. in a plug/socket)
         |                 may also have a pin number nect to it

     ---N/O---          = Normally open (make) switch
     ---N/C---          = Normally closed (break) switch

     ---####---   #     = Resistor (may have value next to it)

          |         |
          V         #
     ---####---  -->#   = Potentiometer (may have value next to it)
                    #      (not strictly the same as a variable
                    |      resistor, incidentally)
     ---|>+---          = Diode (the + represents the end with the
                                  line on the real thing)

     ---||---    ===    = Capacitor (may have value)

          +      |+
     ---||---   ===     = Electrolytic capacitor
                 |         (+ represents the anode)

        ---SS---           = Schmitt triggered gate
                         The actual schematic will either have
                         more details or will be followed by a
                         full pinout for the IC

A rectangular box will often represent an IC. Use your common sense on
these ones, or mail me if you're really stuck.

I will be using the following abbreviations:-

     bk      black
     bn      brown
     rd      red
     or      orange
     ye      yellow
     gn      green
     bu      blue
     vi      violet
     wh      white
     gy      grey
     pi      pink
Anything preceded by a "l" or "d" is light or dark respectively (e.g.
lbu = light blue). Also:-

     m      milli e.g. mA = milliamps
     u      micro e.g. uF = microfarads
     p      pica
     n      nano
     k      kilo
     M      mega
A value of 4k7, for example, means 4.7 kilo Ohms. Although the Ohms are
not mentioned explicitly, units can be guessed from the component type
(Ohms for resistors, Farads for capacitors).

1.6      Construction tips

Not many of these at present, but:-

1)      When soldering to 15 pin, high density D connectors, try to do
     the middle row and middle pins first. If you do it with the
     outside pins first, you'll soon work out why ;)
2)      Owing to the case design of Atari equipment, the "wings" of
     standard 9 & 15 pin connectors often hit the plastic. Either
     move the connectors on the circuit board, or bend the wings
     back on the free plug or socket.

3)      If you do bend the wings back, you'll find it hard to get
     standard hoods to fit. Try (-AFTER- you've tested everything)
     sealing the connectors in epoxy resin, such as Araldite.

2.1      What is an enhanced joystick port (EJP)?

An EJP is a port found on the left hand side of some Atari
computers, on the front of the Atari Jaguar games console, and on
some Atari clone computers. It is a greatly enhanced joystick port
which is capable of supporting all manner of input, and even output
devices, both analogue and digital, and as such is perfect for games
usage with an appropriate controller.

2.2      What machines have them?

The following machines are known to posess EJPs:-

     o The Atari STe (NOT the Mega STe)
     o The Atari Falcon030

     o The Atari Jaguar games console

     o The C-Lab Falcon mk II, and other C-LAB Falcon clones

[can anyone else expand on this list, with other third party

2.3      What about other machines?

There have been several other machines in the Atari range that do
not posess EJPs by default, such as the STFM, TT, STacy, etc.

Most software that supports the EJPs determines their presence by
checking the machine type, and ensuring that it is an STe or Falcon.
The memory locations used for accessing the EJPs are, however, unused
on other machines (at least, according to "The Atari Compendium"), so
it is conceivable that they could be "retro-fitted" to another
machine, such as a Mega STe or TT.

It is also conceivable that EJPs could be added, but mapped to
different memory locations - which would allow additional EJPs to be
added to STes or Falcons. In order to anticipate this possibility, I
am proposing that all new software that is designed to use the EJPs
should not only check the machine type, but ALSO check for a cookie
called "EJPx" where x is a number from 0 to 9. There are some cases
(detailed later) in which it would be useful to obtain more
information about the existing ports, so it is recommended that any
drivers designed to use the existing ports should install a cookie of
"EJP0". A driver for an additional EJP should install the next
sequential cookie, so if "EJP1" does not exist, then there are no
extra EJPs.

I have yet to finalise the information that will be contained in the
cookie, although it is likely that the cookie value will be a
pointer to a structure giving further details about the extra ports.
For example, the structure will contain information about the number
of ports added, their addresses, and their capabilities (some may
only support the digital I/O, for example).

If you have any suggestions or ideas for the information that should
be stored, and how it should be arranged, then please contact me.

2.4      What is the pinout of an EJP?

An EJP is a female 15 pin high density D connector. The connector on
the joypad or other device to plug into it is consequently a male
high density 15 pin D connector. It should be noted that high
density 15 pin connectors have three rows of five pins in the same
size shell as the 9 pin connectors used for the normal mouse and
joystick conncetions on an Atari computer. They should not be
confused with the normal density 15 pin connectors, which have two
rows of pins, and are physically larger.

Owing to the shape and size of the cutouts for the connectors on the
computer, most 15 pin connectors will hit the plastic with their
"wings". The best solution I have found for this is to bend the
"wings" backwards, and encase the soldered joints, wings and part of
the body in an epoxy resin, such as "Araldite". This produces a
solid and sturdy plug unit - but ensure the device is working before
you do this, as it is practically irreversible once set.

Looking into the port on the computer, the connector looks something
like this:-

     \          *       *       *      *      *       /
      \         5       4       3      2      1      /
       \                                            /
        \          *       *       *      *     *  /
         \        10       9       8      7     6 /
          \                                      /
           \   *       *       *      *      *  /
            \ 15      14      13     12     11 /

The pins are nominally allocated as follows. Please note, however,
that this is according to the Falcon030 manual, and does not
necessarily relate to the pin usage in some of the projects and
adaptors desribed in the rest of this FAQ.

           PORT A                        PORT B
           ======                        ======

      1 - UP 0                   1 - UP 1
      2 - DOWN 0                   2 - DOWN 1
      3 - LEFT 0                   3 - LEFT 1
      4 - RIGHT 0                   4 - RIGHT 1
      5 - PADDLE 0 : Y AXIS             5 - PADDLE 1 : Y AXIS
      6 - FIRE 0/LIGHT GUN             6 - FIRE 1
      7 - Vcc (+5V DC)             7 - Vcc (+5V DC)
      8 - Not connected             8 - Not connected
      9 - GROUND                   9 - GROUND
     10 - FIRE 2                  10 - FIRE 3
     11 - UP 2                  11 - UP 3
     12 - DOWN 2                  12 - DOWN 3
     13 - LEFT 2                  13 - LEFT 3
     14 - RIGHT 2                  14 - RIGHT 3
     15 - PADDLE 0 : X AXIS            15 - PADDLE 1 : X AXIS

2.5      What can they be used for?

Quite a lot really. The pin description above only tells half the
story - each port actually consists of a pair of analogue to digital
convertors, as well as a number of digital input lines and digital
output lines. In principal, therefore, the EJPs can be wired up to
form a quite sophisticated I/O port. A number of resolution
enhancers for the Falcon rely on this fact.

In practice, it would be more usual to connect them to tried and
tested I/O devices, the most common being joypads, joysticks,
paddles and light pens. These are all described below.

3.1      Jaguar joypads

These are the controllers that Atari designed to be used with their
Jaguar games console. Somewhat sensibly, they made them compatible
with the "old" STe and Falcon EJPs, with the result that a number of
games on these machines now support them. The joypad is a fairly
bulky device, designed to be held firmly in both hands.

On the top left is the direction pad, which allows the usual
joystick style 8-way movement (UP, DOWN, LEFT, RIGHT). The top right
sports three fire buttons (A, B and C), with B being used as the
main fire button in most games. This may seem a little strange, but
the idea is that it is easy to move to either of the other buttons
from B.

Between these two areas there are PAUSE and OPTION buttons. There is
also a 12 button numeric keypad on the lower part of the unit, with
the numbers 0-9 (telephone style) and * and # in the lower left and
right corners respectively.

There is also a "procontroller" which has three additional fire
buttons, X, Y and Z, as well as a pair of "sidestep" buttons, L and R,
which are on the top of the unit.


     Concerning the usage of the buttons. Where possible, it would
     be best to use the same systems used on the Jaguar, to make
     things easier for people using both platforms. As has already
     been stated, B should be programmed as the main fire button
     (or an option should allow the user to choose the function of
     each fire button)
     The PAUSE button, strangely enough should pause the gameplay,
     if this is an option. If a message appears on screen during
     pause mode, pressing 1+3 (i.e. 1 and 3 together) should remove
     it, but still leave the game paused.
     0 should be used to toggle music on and off.
     *+# (* and # together) should reset the game, and should take
     priority over "0" since at least one of the projects outlined
     below has the option to make the computer think that all
     three buttons have been pressed, in order to reset the game.
     To account for users with a procontroller, X is mapped to 9, Y
     to 8 and Z to 7. L and R are mapped to 4 and 6 respectively.
     Please also note that the joypad need not only be used for
     games. Any software requiring a "remote control" would benefit
     from it - e.g. sequencers.

3.2      So how does a joypad work?

A joypad essentially consists of a matrix of 4 groups of 5 buttons,
plus one group of 6 buttons. These groups are arranged as follows:-

     Group 3:FIRE B, *, 7, 4, 1
     Group 2:FIRE C, 0, 8, 5, 2
     Group 1:OPTION, #, 9, 6, 3

Only one group can be read at any one time, so to read the entire
joypad, four reads have to be made. The reason for this is to do with
the fact that Atari decided to make the joypad with 21 buttons, but a
15 pin plug. At first it may seem impossible to fit the signals from
21 buttons, plus the 0V and 5V lines into a 15 pin plug, but it can be
done, using a system called multiplexing.

A multiplexer is simply a form of digital switch. It has a number of
"control inputs", a number of "data inputs", and a number of "data
outputs". The control lines are used to provide a code which will
determine which of the inputs is routed to which of the outputs. For
example, consider the following simple multiplexer:-

           I1 ------|             |
                    | MULTIPLEXER |---------- Q1
           I2 ------|             |
           C1 -------------+

Now, assume C1 is HIGH (this is a binary system, so it can only have
two states, LOW (0) or HIGH (1) ). If this is the case, whatever
signal is applied to I1 will be routed to the output, Q1. If C1 is
switched to LOW then the signal on I2 is routed to Q1.

Now imagine that the two inputs are connected to switches, and that
the output is connected to the host computer. By simply changing C1,
via an OUTPUT from the computer, it is possible to read both
switches using only one INPUT.

The multiplexer in the joypad works in a similar manner, except that
it has four control lines, six output lines, and twenty-one input
lines (the switches). To read any particular group of switches, you
first write a value to the control lines. Writing a value which
takes only the first control line low will enable you to read the
six switches in group 1. Taking only the second control line low
will enable you to read the switches in group 2, and so on.

Matters are inevitably complicated, however, by the actual hardware
configuration used in the STe and Falcon. There are, as you know,
two EJPs on these machines, and Atari chose, quite sensibly, to
combine their addresses in in the memory map. In order to read
joypads on these machines, therefore, you must do the following:-

     1)      Write a value to address 0xFF9202. This sets the
           control lines on the multiplexers.
     2)      Read the values at 0xFF9200 and/or 0xFF9202. These
           will have certain bits cleared (set to LOW) to
           indicate which switches in a group are being pressed.

The value that you write in step one is made up as follows: it is a
long, whose lower four bits represent the control inputs of joypad A,
and whose next four bits (5-7) represent the control inputs of joypad
B. For example:-

     0xFFFE      Selects group 4, joypad A for reading
     0xFFFD      Selects group 3, joypad A
     0xFFFB      Selects group 2, joypad A
     0xFFF7      Selects group 1, joypad A
     0xFFEF      Selects group 4, joypad B for reading
     0xFFDF      Selects group 3, joypad B
     0xFFBF      Selects group 2, joypad B
     0XFF7F      Selects group 1, joypad B

Xav's Hint #1

Although not officially documented, it should be possible to combine
these values as below. Please note that I have not tried this myself,
so can offer no guarantees, but I see no reason for it not to work.

     0xFFEE      Selects group 4, joypads A and B
     0XFFB7      Selects group 2, joypad B and group 1, joypad A

Xav's Hint #2

Another thing that is possible is the reading of multiple groups
simultaneously. For example, setting bit 0 low selects port A group 4.
Similarly, bit 1 selects port A group 3, and bit 2 selects port A
group 2. Therefore, setting all three of these bits low, by writing a
value of 0xFFF8, should give an output when a button in group 4 OR
group 3 OR group 2 is pressed. I.e.

     o      Write 0xFFF8
     o      Read from 0xFF9200
     o      If bit 1 is clear, then the user pressed fire button
           A, or fire button B, or fire button C.
This method can therefore be used in a situation where your program
only needs to respond to one button, either because the game design is
such that one button is all that is needed, or at screens where you
might present a message saying "Press Any Fire Button To Continue".

If you think about these two points a little, you'll see that they add
a great deal of flexibility to the joypads, allowing you to read
buttons more easily in most circumstances than is at first apparent.

     The second hint will not work if the player has a "Team Tap"
     connected (see below). It does, however, provide a means of
     testing whether or not there is a "Team Tap" connected because
     of the change in behaviour. You should not, therefore, write
     code which relies on hint 2, since the "Team Tap" is
     transparent to "normal" code. That is, if you test for each
     group individually, rather than checking for a button in group
     1 OR group 2 (for example) in one go, your code will work
     whether there is a "Team Tap" present or not.
     You can, however, still check both controllers in one pass
     (hint 1).
     See the section below on the "Team Tap" for more details.

Once you have written the requisite mask to 0xFF9202, you can read
back the state of the joypad(s) from 0xFF9200 and 0xFF9202. Since the
joypad works on NEGATIVE LOGIC, a bit is CLEARED whenever a button is
pressed. In the table below, the first letter indicates the port that
is being read, so A FIRE B represents fire button B on the joypad
attached to port A. The exact bit that is cleared determines which
button has been pressed as follows:-

     Group 4            Group 3            Group 2      Group 1
     =======            =======            =======            =======


Bit 0      A PAUSE              N/A              N/A              N/A

Bit 1      A FIRE A      A FIRE B      A FIRE C      A OPTION

Bit 2      B PAUSE              N/A              N/A              N/A

Bit 3      B FIRE A      B FIRE B      B FIRE C      B OPTION


Bit 8      A UP              A *              A 0              A #

Bit 9      A DOWN              A 7              A 8              A 9

Bit 10      A LEFT              A 4              A 5              A 6

Bit 11      A RIGHT              A 1              A 2              A 3

Bit 12      B UP              B *              B 0              B #

Bit 13      B DOWN              B 7              B 8              B 9

Bit 14      B LEFT              B 4              B 5              B 6

Bit 15      B RIGHT              B 1              B 2              B 3

Okay, so having probably confused everyone now, here's the summary. To
read a joypad, simply write a value to 0xFF9202 with bit 0, 1, 2 or 3
low (and/or 4, 5, 6 or 7 for port B) depending on which group you want
to read. Next read from 0xFF9200 and/or 0xFF9202 to obtain a bitmask
giving the buttons in that group that were pressed, as in the table
above. Clear as Guinness or what!!?!??

3.3      Example joypad code

This is a _very_ basic bit of C to read the joypad ports. MASK should
be replaced with the correct bitmask for the group(s) you wish to
read, which would normally be #define'd elsewhere to make the code
easier to read. Note: You must be in supervisor mode to access the
ports, so either use Super() as below, or Supexec on a whole function.
Normally you would use a function like this to repeatedly read each
port and/or each group, and fill an array or structure which can then
be used by the rest of the program.

In this instance the values of firebuttons (0xFF9200) and keypad
(0xFF9202) are simply printed to the screen. Usually you would do
something a little more useful with them!

**      Start of example code

void main (void)
     void *stack_address;
     short *mask_address = (short *)0xFF9202;
     short *firebuttons = (short *)0xFF9200;
     short *keypad = (short *)0xFF9202;
     unsigned short firebuttons_pressed;
     usnogned short keypad_pressed;
     while(1)      /* Just to make the test code repeat      */
           /* Go into supervisor mode      */
           stack_address = Super(NULL);
                 /* Write the mask value      */
                 *mask_address = MASK;
                 /* And read the results      */
                 firebuttons_pressed = *firebuttons;
                 keypad_pressed = *keypad;                  
           /* Return from supervisor mode      */
           /* Print the result            */
           printf("\nFirebuttons = %d, Keypad = %d",
                       firebuttons_pressed, keypad_pressed);
**      End of example code

3.4      Joypad circuit diagram

NOTE: This circuit diagram has been obtained by dissecting a joypad,
and is provided for information purposes only. If you use this design
in order to produce your own joypad or other device, I cannot be held
responsible for any infringement of patents or other legal
implications that may arise.

15 Pin High Density
D Socket

7 O---------*---------*--*--*--*--*--+
             |         |  |  |  |  |  |
1 O---------|---------|--|--|--|--|--|---------------------+
2 O---------|---------|--|--|--|--|--|---------------------|--+
3 O---------|---------|--|--|--|--|--|---------------------|--|--+
4 O---------|---------|--|--|--|--|--|---------------------|--|--|--+
             |         |  |  |  |  |  |                     |  |  |  |
             |         |  |  |  |  |  |       *--|>+--N/O---*  |  |  |
             |         |  |  |  |  |  |       |     (OPTION)|  |  |  |
             |         |  |  |  |  |  |       |             |  |  |  |
             | 20      |  |  |  |  |  |       *--|>+--N/O---|--*  |  |
        +----+----+    |  |  |  |  |  |       |       (C)   |  |  |  |
        |         |    #  #  #  #  #  # All   |             |  |  |  |
        | 74HC244 |    #  #  #  #  #  # 4k7   *--|>+--N/O---|--|--*  |
        |         |    #  #  #  #  #  #       |       (B)   |  |  |  |
      16|         |4   |  |  |  |  |  |       |             |  |  |  |
10 O----+---SS----+----*--|--|--|--|--|-------*--|>+--N/O---|--|--|--*
        |         |       |  |  |  |  |               (A)   |  |  |  |
        |         |       |  |  |  |  |                     |  |  |  |
        |         |       |  |  |  |  |       *--|>+--N/O---*  |  |  |
        |         |       |  |  |  |  |       |       (3)   |  |  |  |
        |         |       |  |  |  |  |       |             |  |  |  |
        |         |       |  |  |  |  |       *--|>+--N/O---|--*  |  |
        |         |       |  |  |  |  |       |       (2)   |  |  |  |
        |         |       |  |  |  |  |       |             |  |  |  |
        |         |       |  |  |  |  |       *--|>+--N/O---|--|--*  |
        |         |       |  |  |  |  |       |       (1)   |  |  |  |
       6|         |14     |  |  |  |  |       |             |  |  |  |
11 O----+---SS----+-------*--|--|--|--|-------*--|>+--N/O---|--|--|--*
        |         |          |  |  |  |             (RIGHT) |  |  |  |
        |         |          |  |  |  |                     |  |  |  |
        |         |          |  |  |  |       *--|>+--N/O---*  |  |  |
        |         |          |  |  |  |       |       (6)   |  |  |  |
        |         |          |  |  |  |       |             |  |  |  |
        |         |          |  |  |  |       *--|>+--N/O---|--*  |  |
        |         |          |  |  |  |       |       (5)   |  |  |  |
        |         |          |  |  |  |       |             |  |  |  |
        |         |          |  |  |  |       *--|>+--N/O---|--|--*  |
        |         |          |  |  |  |       |       (4)   |  |  |  |
      12|         |8         |  |  |  |       |             |  |  |  |
12 O----+---SS----+----------*--|--|--|-------*--|>+--N/O---|--|--|--*
        |         |             |  |  |              (LEFT) |  |  |  |
        |         |             |  |  |                     |  |  |  |
        |         |             |  |  |       *--|>+--N/O---*  |  |  |
        |         |             |  |  |       |       (9)   |  |  |  |
        |         |             |  |  |       |             |  |  |  |
        |         |             |  |  |       *--|>+--N/O---|--*  |  |
        |         |             |  |  |       |       (8)   |  |  |  |
        |         |             |  |  |       |             |  |  |  |
        |         |             |  |  |       *--|>+--N/O---|--|--*  |
        |         |             |  |  |       |       (7)   |  |  |  |
       9|         |11           |  |  |       |             |  |  |  |
13 O----+---SS----+-------------*--|--|-------*--|>+--N/O---|--|--|--*
        |         |                |  |              (DOWN) |  |  |  |
        |         |                |  |                     |  |  |  |
        |         |                |  |       *--|>+--N/O---+  |  |  |
        |         |                |  |       |       (#)      |  |  |
        |         |                |  |       |                |  |  |
        |         |                |  |       *--|>+--N/O------+  |  |
        |         |                |  |       |       (0)         |  |
        |         |                |  |       |                   |  |
        |         |                |  |       *--|>+--N/O---------+  |
        |         |                |  |       |       (*)            |
       7|         |13              |  |       |                      |
14 O----+---SS----+----------------*--|-------*--|>+--N/O------------*
        |         |                   |               (UP)           |
        |         |                   |                              |
      18|         |2                  |                              |
6  O----+---SS----+-------------------*----------|>+--N/O------------+
        |         |                                 (PAUSE)          
        |         |
        |         |10
        |         +-----+
        |         |     |
        +-+---+---+     |
         1|   |19       |
       |   |         |
       |   |         |
9 O------*---*---------+

3.5      Using joypads as normal joysticks

One of the reasons that not many people have bought joypads for their
STes or Falcons is the lack of software that supports them. Whilst a
great many programs support the "old" joystick ports, only the very
latest software supports the EJPs. It would therefore be very useful
if a joypad could be used in an "old" joystick port, since the
purchase of one joypad would get you a device that can be used in
either type of port.

This was exactly the sort of thing that I wanted to do with my own
joypad when I bought it, so I designed the (wait for it...)
"Padaptor". Sad name, maybe, but it's cheap and easy to make.

3.6      Joypad -> joystick adaptor circuit diagram

     15 pin high density                  9 pin D
          D socket                        socket

           14 O------------------------------O 1
           13 O------------------------------O 2
           12 O------------------------------O 3
           11 O------------------------------O 4
           10 O------------------------------O 6
            7 O------------------------------O 7
            9 O----------------*-------------O 8
            4 O----------------*
            3 O----------------*
            2 O----------------+

This works because the joypad and the joystick both work on "negative
logic" - i.e. a LOW value is considered to be TRUE. By connecting the
control lines of the joypad to 0V, all the buttons are effectively
ORed together. For use as a joystick, this allows you to use UP, DOWN,
LEFT, RIGHT and any of the fire buttons. Several of the other buttons
will also mirror these effects, although that should not cause any

3.7      Programs which use joypads

This section will be used to provide a list of programs for the STe
and Falcon which will use a joypad if available. The first column will
contain either an "o", indicating that a joypad is optional, and that
another means of control is also available. A "c" indicates that a
joypad is compulsory, and the game cannot be played without one. An
"m1", "m2" etc. indicates that a joypad is required for multiplayer
mode - i.e. a joypad is needed for more than one player (in the first
case) or more than two players (in the second). A "?", unsurprisingly,
means that I don't any information available, so if anyone can help...

Games for the Jaguar are not listed, because it can be reasonably
assumed that all Jaguar games support the joypad.

This list is _very_ sparse at the moment (due to time), and I would be
grateful if people could email me the details of any programs I have
not listed. In the case of PD, freeware or shareware, an address or
FTP site where it can be obtained would be useful.

     PD/Shareware, Etc.
     ?      Double Bobble
           By Resevoir Gods

     ?      Super Bomber Man
           By Marc Bolion

     ?      BioHazard 2
           By Les Greenhalgh/Village Software
             STF coverdisk 83
     ?      Tron 2000
           (preview - not finished yet)

     ?      STOS Falcon Extension
           (not a game, of course!)
     Bad Mood will support the Joypad... (2.06c has joypad support...)
     ?      Evolution Dino Dudes
           Published by 16/32
     c      Llamazap
           Published by 16/32
     ?      Gravon

             demo at:

     ?      Multi-Briques
           By Parx

             demo at:

     ?      Ping 2000
           By Holland Game Design

             demo at:

     ?      Steel Talons
           Published by 16/32

             demo at:

     ?      Willies Adventures
           (preview - not finished yet)
           By New Beat Development

     ?      X-Moon
           (preview - not finished yet)

     o      Moonspeeder
           From Merlin

             demo at:

     c      Rock'N'Roll Clams
           Published by Caspian Software
     c      Zero-5
           Published by Caspian Software
There is also a program available that allows the joypad to be used in
place of the mouse. Whilst this is not practical for day to day use,
it can be very handy for mouse based multiplayer games (such as Triple
Yahoo, for example) since the mouse still works too, so more than one
player can have their own controls, rather than all huddling round the
mouse. In fact, with enough serial ports, a graphics tablet and a
serial mouse, it is possible to have 4 devices all controlling the
mouse pointer! Can anyone supply the name and an FTP location for this
program, please? It is available from Floppyshop in the UK, but I
don't know the disk number, unfortunately.

Once the format of the "EJP0" cookie has been finalised (see above,
and in the light pen section) it would be useful to have a program
that uses the joypad as a mouse, but which also installs the cookie,
so could either the programmer of the above application, or someone
who is prepared to write a new one, contact me.

4.1      Jaguar team tap

Atari have released a multiplayer adaptor for use with the Jaguar,
which they have called the "Team Tap" (TT). The TT allows up to four
joypads to be plugged into each socket on the Jaguar, giving a
theoretical maximum of eight players.

The TT is bundled "free" with the basketball game "White Men Can't
Jump", and is also supposedly available separately. For Falcon and STe
owners who cannot find one on sale without the game, or for anyone who
is interested or who needs to repair a TT, the circuit diagram

On an STe or Falcon, I am adopting the following standard for
referring to the TT outputs. I will be using a two letter code, where
the first represents the joypad port on the computer and the second
represents the joypad port on the TT. Possible values are therefore

The way the TT works is to fully decode the four control lines that
the joypad uses. By "fully decode", I mean that all 16 binary
addresses are available with the TT, giving access to four
controllers, each with four groups of buttons. Consequently, trick 2
in the joypad section will no longer work, since writing to the
control lines with a value of (say) 0xFFF8 will no longer set all
three lower control lines LOW on one joypad. Instead it will access
group 1 of joypad AC.

The decoding has been designed so that "normal" reads from the joypad
will work fine on AA or BA, even if the TT is in place. In other
words, using mask values of 0xFFFE, 0xFFFD, 0xFFFB or 0xFFF7 for
example, will all work fine with the first joypad in port A, whether
or not it is connected through a TT (in which case it is joypad AA).

The full list of codes is as follows, as #defines for C programmers ;)

#define      portAA_group4      0xFFFE      /*      ...11111110      */
#define      portAA_group3      0xFFFD      /*      ...11111101      */
#define      portAA_group2      0xFFFB      /*      ...11111011      */
#define      portAA_group1      0xFFF7      /*      ...11110111      */

#define      portAB_group4      0xFFF0      /*      ...11110000      */
#define      portAB_group3      0xFFF1      /*      ...11110001      */
#define      portAB_group2      0xFFF2      /*      ...11110010      */
#define      portAB_group1      0xFFF3      /*      ...11110011      */

#define      portAC_group4      0xFFF4      /*      ...11110100      */
#define      portAC_group3      0xFFF5      /*      ...11110101      */
#define      portAC_group2      0xFFF6      /*      ...11110110      */
#define      portAC_group1      0xFFF8      /*      ...11111000      */

#define      portAD_group4      0xFFF9      /*      ...11111001      */
#define      portAD_group3      0xFFFA      /*      ...11111010      */
#define      portAD_group2      0xFFFC      /*      ...11111100      */
#define      portAD_group1      0xFFFF      /*      ...11111111      */

#define      portBA_group4      0xFFEF      /*      ...11101111      */
#define      portBA_group3      0xFFDF      /*      ...11011111      */
#define      portBA_group2      0xFFBF      /*      ...10111111      */
#define      portBA_group1      0xFF7F      /*      ...01111111      */

#define      portBB_group4      0xFF0F      /*      ...00001111      */
#define      portBB_group3      0xFF1F      /*      ...00011111      */
#define      portBB_group2      0xFF2F      /*      ...00101111      */
#define      portBB_group1      0xFF3F      /*      ...00111111      */

#define      portBC_group4      0xFF4F      /*      ...01001111      */
#define      portBC_group3      0xFF5F      /*      ...01011111      */
#define      portBC_group2      0xFF6F      /*      ...01101111      */
#define      portBC_group1      0xFF8F      /*      ...10001111      */

#define      portBD_group4      0xFF9F      /*      ...10011111      */
#define      portBD_group3      0xFFAF      /*      ...10101111      */
#define      portBD_group2      0xFFCF      /*      ...11001111      */
#define      portBD_group1      0xFFFF      /*      ...11111111      */

Simply write the required code to 0xFF9202, then read from 0xFF9200
and 0xFF9202 as usual.

In order to determine whether or not a TT is present, you need to be a
little bit sneaky. Since there is no flag (that I have found, at
least) that is set or cleared by the addition of the TT, you need to
check for its existance based on the change of behaviour of the
computer when it is added. Below is one method for doing this:-

o      Display some sort of title screen, and request that a player
     presses a key on the first joypad in that port (for example
     "Press B on the first joypad to continue").
o      This will involve sending a mask with bit 1 cleared (B is in
     group 3), for port A.
o      As soon as you register the keypress for button B, test for
     another combination that has bit 1 cleared. For example, you
     could write a mask of 0xFFF8, which has bits 0, 1 and 2
     cleared. If there is just a normal joypad attached, this will
     be decoded as an OR, as in hint 2 in the joypad section. The
     result is that you should still be registering button B as
     being pressed, since it will register if button A OR B OR C is
     pressed in this instance.
o      If you do not register button B as still being pressed, then
     either they let go of it very quickly, or they have a TT, in
     which case the value 0xFFF8 will be decoded to check another
     joypad. It is possible that the other joypad will also have B
     depressed, but if your code works fast enough, you should be
     able to check several combinations of masks with bit 1
     cleared, before the B button is released. This reduces the
     likelihood of inadvertantly thinking there is a TT present,
     when there isn't.
o      In addition, repeating this procedure, by going through any
     necessary option screens or title screens _before_ the player
     chooses the number of competitors, will increase your chances
     of correctly identifying the existance of a TT.

If anyone knows a better way to check for the existance of a TT, I'd
be happy to hear it!

[edit]ggn's note: here you go matey :)[/edit]

Code (]

4.2      Example team tap code

Simply use the normal joypad code, but for MASK, insert one of the
labels that are #define'd above. The values returned are of the same
format as for a normal joypad, so the table in that section applies.

4.3      Team tap circuit diagram


4.4      Programs which can use a team tap

Only a couple of Jaguar games at the moment. If you are writing
anything that will use a TT, please let me know.

     o      White Men Can't jump
           Jaguar basketball game
           Published by Atari
           Comes supplied with a "free" team tap
     o      NBA Jam
           Jaguar basketball game
           Said to play better (but look and sound a little
           worse) than the Playstation version ;)

5.1      Using joysticks with an EJP

There are a couple of ways to use joysticks with EJPs. The first is
to simply wire them as joypads, in which case either use the circuit
diagram above, or wire each switch in parallel with its counterpart in
a _real_ joypad.

The other way is by means of an adaptor. This device will allow you to
use two normal joysticks in a single EJP. New games should really use
the code for a team tap if they need extra players, but the details
for this adaptor are included here for completeness. As far as I know
there is only one game that supports this system, although the game is
so good that it makes it worthwhile. The game is "Dynablasters" and
involves you trying to blow your friends up for no apparent reason.
Using two of these adaptors, up to six people can play the game -
which is damned good fun!

5.2      Example joystick code

I haven't looked into how to read this adaptor, but from the circuit
diagram I would guess that you read from 0xFF9200 and 0xFF9202, but
that you _do not_ have to write a mask first. Reading 0xFF9200 would
give the following:-

     Bit 0 clear      FIRE, joystick 1, port A
     Bit 1 clear      FIRE, joystick 2, port A
     Bit 2 clear      FIRE, joystick 1, port B
     Bit 3 clear      FIRE, joystick 2, port B

The other values are returned from 0xFF9202 as follows:-

     Bit 0 clear      UP, joystick 1, port A
     Bit 1 clear      DOWN, joystick 1, port A
     Bit 2 clear      LEFT, joystick 1, port A
     Bit 3 clear      RIGHT, joystick 1, port A
     Bit 4 clear      UP, joystick 1, port B
     Bit 5 clear      DOWN, joystick 1, port B
     Bit 6 clear      LEFT, joystick 1, port B
     Bit 7 clear      RIGHT, joystick 1, port B
     Bit 8 clear      RIGHT, joystick 2, port A
     Bit 9 clear      LEFT, joystick 2, port A
     Bit 10 clear      DOWN, joystick 2, port A
     Bit 11 clear      UP, joystick 2, port A
     Bit 12 clear      RIGHT, joystick 2, port B
     Bit 13 clear      LEFT, joystick 2, port B
     Bit 14 clear      DOWN, joystick 2, port B
     Bit 15 clear      UP, joystick 2, port B

This information is purely speculation based on the circuit diagram
for the adaptor. I have not tried to read from one of these devices
myself. This information is provided as a starting point for anyone
who may wish to investigate further, however if you have any more
information, or if you find any errors in my guesswork, please let me

5.3      Joystick -> EJP adaptor circuit diagram

Get five friends, six joysticks, two adaptors, a copy of Dynablasters
and HAVE FUN!!! If you don't have that many joysticks, but do have a
joypad, bear in mind that you can use the "Padaptor" described above -
or even incorporate it into this design.

     15 pin high density                  9 pin D plug
          D plug                        (joystick 1)

            1 O------------------------------O 1      UP
            2 O------------------------------O 2      DOWN
            3 O------------------------------O 3      LEFT
            4 O------------------------------O 4      RIGHT
            6 O------------------------------O 6      FIRE
            9 O----------------*-------------O 8      GROUND
                               |           9 pin D plug
                               |           (joystick 2)
                               +-------------O 8      GROUND
           10 O------------------------------O 6      FIRE
           11 O------------------------------O 1      UP
           12 O------------------------------O 2      DOWN
           13 O------------------------------O 3      LEFT
           14 O------------------------------O 4      RIGHT

6.1      Analogue joysticks

Each of the EJPs has a pair of analogue to digital convertors (ADCs).
These are capable of taking a continuously varying input, and
converting it to a digital value from 0 to 255. The easiest way to
provide this continuously varying input is via a potentiomer. This is
a variable resistance connected across the supply rails, with an
output tapped off from a "wiper" that can move along the track of
resisting material. The result is that the output from this wiper can
be swung (theoretically) from 0V to 5V. In practice these extremes are
not available due to other resistances in the system, and the physical
restrictions of potentiometers themselves.

By arranging two such potentiometers, one connected to each ADC, at 90
degrees to each other, a linkage can be made in the form of a
joystick, whereby any point in a square area can be categorised by a
pair of x and y voltages. These voltages are supplied to the ADCs, and
the application can then obtain an absolute value for the position of
the joystick at any given time.

The difference betweenthis and "normal" joysticks is that a normal, or
"digital" joystick works by using switches. Depending on the direction
the stick is pushed in, none, one or two switches will close, and the
computer interprets this as a relative command - "I want to move in
this direction". The speed at which you move is dictated by the
mechanics of the game, not by how fast you move the stick. With an
analogue stick, however, you are giving an absolute position - "I want
to be at coordinates (x, y)" - so the speed of your movement is
(usually) dependent on the speed at which you move the stick.

Digital joysticks work fine for most games, but some, such as flight
simulators, work best with analogue sticks. Analogue sticks went out
of fashion for a while, but many PC games now use them, so you can
probably adapt a PC stick to suit the EJP.

6.2      Example analogue joystick code

Below is the code for reading this, however the fire buttons are read
in the same way as for the joypad, so are not covered. "The Atari
Compendium" contains an error on the addresses of the analogue stick
information, though the memory map at the back is correct. Essentially
you need to read from the following addresses:-

     0xFF9210      Joystick A, X direction
     0xFF9212      Joystick A, Y direction
     0xFF9214      Joystick B, X direction
     0xFF9216      Joystick B, Y direction
These will return values from 0 to 255, where 0,0 represents the
bottom left and 255,255 is the top right [can someone confirm this?):

With regard to the fire buttons on an analogue joystick, no standards
have been set by Atari. The inputs to the ADCs use "spare" pins that
are otherwise unused on the joypad, so it would actually be possible
to have a full set of 21 buttons (or even 24 if the PAUSE line was
fully decoded!). In practice I would suggest that if you are writing
any games for an analogue joystick, that you can assume that the three
fire buttons will be present, and that any other buttons (pause,
option and numeric keypad) should have their functions duplicated on
the STe or Falcon keyboard, in case they are not present on the

**      Code to read an analogue joystick on an STe or Falcon
**      By Xav

void main (void)
     void *stack_address;
     short *x_axisA = (short *)0xFF9210;
     short *y_axisA = (short *)0xFF9212;
     unsigned char x_axis_returned;
     unsigned char y_axis_returned;
           /* Supervisor mode      */
           stack_address = Super(NULL);
                 /* Read the ports      */
                 x_axis_returned = *x_axisA;
                 y_axis_returned = *y_axisA;                  
           /* Return to user mode      */
           /* Display the results      */
           printf("\nX Axis = %d, Y Axis = %d",
                 x_axis_returned, y_axis_returned);

**      End of example code

6.3      Analogue joystick circuit diagram

In the meantime, if anyone with a PC analogue joystick could hack it
open and let me know what potentiometers are in there, I'd appreciate
it! I.e. their value (1Meg, 470k, etc) type (Lin or Log) and how many
connections are made to it (probably 2 or 3).

6.4      Programs which will use an analogue joystick

     o      Moonspeeder
           From Merlin

             demo at:

7.1      Digital paddles

Paddles are another term for rotary controllers, and like joysticks
they come in both analogue and digital forms. Essentially a paddle has
a wheel that you turn, which is represented on screen by either
something turning, or something moving (usually linearly). It also has
one or more buttons, for firing, etc.

A digital paddle can be revolved contiually in either direction, i.e.
there are no end "stops". They give a relative direction of the form
"I am moving up/left/clockwise" or "I am moving
down/right/anticlockwise". They are best used for applications in
which things must be able to move continually, usually cyclically. The
best examples are overhead driving games, such as Indy500 on the Atari
2600 games console (which had a pair of digital "driving" paddles
supplied with it), or games such as Tempest.

And yes, in case you're wondering, Tempest 2000 on the Jag does allow
you to use digital paddles.

7.2      Example digital paddle code

A digital paddle is read in exactly the same way as a joypad, it is
simply the interpretation that is different. In order to read a
digital paddle, you will also need some kind of "memory element" - for
example a static variable called last_position.

Essentially the paddle will give out the following sequences:-

     LEFT, NONE, RIGHT, LEFT... for anticlockwise
     RIGHT, NONE, LEFT, RIGHT... for clockwise
As a programmer you simply need to know the last position the paddle
was in. If it is the same as the current one, the paddle has not been
turned, otherwise you can determine which direction it was turned in
from the information above.

For example if the last position was with "LEFT" apparently pressed,
then if the current position is also LEFT, the paddle has not moved.
If the current position is RIGHT, the paddle has been moved clockwise.
If there are NONE depressed (i.e. neither left nor right), then the
paddle has been moved anticlockwise. Get it?

7.3      Digital paddle circuit diagram

The hardest part about building a digital paddle is tracking down a
suitable rotary switch. It must be capable of complete rotation, and
must be either a "clickless" or "light click" type. It must also have
a single pole, and the number of ways must be divisible by 3 (most
are). For example, in the UK you can buy a "clickless" 1 pole 12 way
switch from Maplin (order code XX45Y, catalogue from W H Smith) for
about a pound.

Incidentally, the more ways the better, as will become clear (i.e. a
24 way is better than a 12 way if you can find one!).

For the Maplin switch, the design is such that it cannot be turned
completely. What you need to do is prise open the two halves of the
body and you'll find a lump on the inside of the body that acts as a
stop against a lump on the shaft. Trim one of these off with a Stanley
knife, and reassemble. The switch should now turn totally (if not,
make sure you've removed the stop ring from below the nut on the main
body - it's a metal ring with a pin which pokes into the body itself).
When disassembling one of these, watch what goes where! It's a simple
device, but it's still possible to reassemble the contacts wrongly.

Once you've obtained and, if necessary, doctored your switch, connect
it up as follows (assuming the pin numbering starts at 1): pin 1
connects to pin 4 and to pin 7 and pin 10 (every third one). Pin 2
connects to 5, 8 and 11. Pins 3, 6, 9 and 12 are left unconnected.
Flyleads are needed from pins 1 and 2 and from the pole.

The remainder of the circuit is as follows:-

15 Pin High Density
D Socket

7 O---------*---------*--*--*--*--*--+
             |         |  |  |  |  |  |
1 O---------|---------|--|--|--|--|--|--------------------+
2 O---------|---------|--|--|--|--|--|--------------------|--+
3 O---------|---------|--|--|--|--|--|--------------------|--|--+
4 O---------|---------|--|--|--|--|--|--------------------|--|--|--+
             |         |  |  |  |  |  |                    |  |  |  |
             |         |  |  |  |  |  |       *--|>+--N/O--+  |  |  |
             |         |  |  |  |  |  |       |     (OPTION)  |  |  |
             |         |  |  |  |  |  |       |               |  |  |
             | 20      |  |  |  |  |  |       *--|>+--N/O-----+  |  |
        +----+----+    |  |  |  |  |  |       |       (C)        |  |
        |         |    #  #  #  #  #  # All   |                  |  |
        | 74HC244 |    #  #  #  #  #  # 4k7   *--|>+--N/O--------+  |
        |         |    #  #  #  #  #  #       |       (B)           |
      16|         |4   |  |  |  |  |  |       |                     |
10 O----+---SS----+----*--|--|--|--|--|-------*--|>+--N/O-----------*
        |         |       |  |  |  |  |               (A)           |
      14|         |6      |  |  |  |  |                             |
11 O----+---SS----+-------*--|--|--|--|----------|>+--N/O----+      |
        |         |          |  |  |  |               (2)    |      |
       7|         |13        |  |  |  |                      |      |
12 O----|---SS----|----------*--|--|--|----------|>+--N/O----*------*
        |         |             |  |  |               (1) (POLE)    |
      18|         |2            |  |  |                             |
6 O----|---SS----|-------------*--|--|----------|>+--N/O-----------+
        |         |                |  |             (PAUSE)
       9|         |11              |  |                              
13 O----|---SS----|----------------*  |
     |         |                   |
      12|         |8                  |
14 O----|---SS----|-------------------+
        |         |
        |         |10
        |         +-----+
        |         |     |
        +-+---+---+     |
         1|   |19       |
       |   |         |
       |   |         |
9 O------*---*---------+

(1), (2) and (POLE) refer to those flyleads you attached to the switch
earlier, remember!

As you may have noticed, this diagram does not include the numeric
keypad of the Jaguar joypad. I didn't bother with it because it is not
really needed for Tempest 2000, which was the real reason I built this
prototype. If you want to add it, you can simply add the switches and
diodes in the same way as for the joypad, which is why pins 13 and 14
are connected through the chip to the pull up resistors. If you never
intend to add a keypad, these pins can be tied permanently HIGH (to
pin 7).

If you don't want to add the keypad, but DO want the reset function of
"* and #" in jaguar games, simply add a N/O switch to pull pin 8 on
the IC LOW (to pin 9 of the 15 pin connector). This has the effect of
making the Jag think that you are pressing *, 0 and # simultaneously.


Unfortunately the resolution of a rotary switch is is not really high
enough to use effectively with Tempest 2000. The result is that you
have to spin the controller a bit too much for any noticeable movement
in the game, since each section of the web requires several "moves" to
make the ship go to the next section. There are a nmber of solutions
to this:-

1)      Work on your muscles and speed to enable you to spin the thing
     like a crazed wildman with hayfever in the middle of a field
     of flowers in the height of summer.
2)      Add an electronic solution. The most obvious one I could come
     up with would consist of a state machine to determine which
     direction the dial is being spun in which in turn gates a
     local oscillator, so that the Jag sees (say) three button
     presses for every notch that the controller is turned through.

3)      Attach the switch to the dial via a set of gears.

4)      Use a higher resolution switch. This might be possible using
     an optical shaft encoder - I'll look into it when I get some
     more money!

5)      Attach the switch to a well sized handle, and a big flywheel
     so that when you spin it, it keeps on spinning. Now _that's_
     the way to play Tempest!
From this, I would suggest that anyone writing a game to support these
controllers should give the user the option of a "scaling factor".
This would take account of anyone using a plain controller, as well as
those using a geared up or altered controller. Note that one full
revolution of a standard controller will pass through 12 "points", in
case that helps you work out how to scale or structure the game.

Strangely, however, Jeff Minter (we're not worthy!) wrote the code for
the rotary controller into T2K based on an adapted Indy500 racing
paddle that Atari supplied. Since the Indy500 paddle also has a 12 way
switch, the resolution should have been too low on that as well, so
either Jeff wanted us all to fit flywheels for the real arcade
experience, or I'm missing something, somewhere.
Note also that digital paddles are basically an adaption of the
joypad, so they will also work with a Team Tap, for multiplayer games
(now, does anyone want to write an 8 player Falcon version of

7.4      Programs which will use a digital paddle

Tempest 2000 on the Jag and, erm, that's about it at the moment!
(But what a game it is!!!!)

8.1      Analogue paddles

An analogue paddle is a rotary controller which only moves through a
restricted range of movement (usually about 270 degrees). It returns
an absolute position of the form "I am currently at an angle of x
degrees". The position is defined as a value between 0 and 255.

Each EJP supports two analogue paddles - they are simply the x and y
potentiometers of an analogue joystick separated into two different
boxes. The problem then comes from the fire buttons, so I would like
to propose the following standard:-

     Paddle 1      Fire A = Joypad Fire A
                 Fire B = Joypad Fire B
                 Fire C = Joypad Fire C
                 Pause  = Joypad Pause
                 Option = Joypad Option
     Paddle 2      Fire A = Joypad 9
                 Fire B = Joypad 8
                 Fire C = Joypad 7
                 Pause  = Joypad 4
                 Option = Joypad 6
The mappings for paddle 2 were chosen to correspond to the mappings
used for the extra buttons on the procontroller, so another way of
looking at it is A=X, B=Y, C=Z, Pause=L and Option=R. Note L & R are
the fingertip buttons, NOT LEFT and RIGHT on the direction pad.

If you choose to build, or support these paddles in your progams,
please use these mappings, since everyone will be working to the same
standard then.

As a guideline, paddles are best used when an object has to move over
a fixed path, from one end to another and back again. The best example
is a game like "Breakout" where the paddle is used to move the bat
left and right. Similarly "Space Invaders" would benefit from a
paddle, and "Circus Atari", for those that remember it, was a superb
paddle based game (a bit like breakout in some respects). A "Pong"
style game would also work well with paddles.

8.2      Example analogue paddle code

Exactly the same as the analogue joystick code, except that x and y
now correspond to paddle 1 and paddle 2. The fire buttons are read as
for the joypad, but please bear in mind the mappings shown above.

Note that both the analogue joystick and analogue paddles (as well as
the light pen, covered below) are incompatible with the team tap.

8.3      Analogue paddle circuit diagram


8.4      Programs which will use an analogue paddle

As far as I know, the really poor version of breakout that came free
with the Falcon supports analogue paddles, but I don't know of
anything else.

Title: Re: The Atari Enhanced Joystick Ports FAQ 0.90
Post by ggn on 12.08.11 at 08:45:18
[code]9.1      Light pens

A light pen is a device that responds to the bright light of the
electron beam in a CRT (i.e. a monitor or television). It relays this
as a pulse back to the computer, which is then able to calculate where
the electron beam, and hence the light pen, were positioned. With a
suitable criver, a light pen could be used in place of a mouse to
"draw" on th screen.

A variation on the same theme is a light gun, which works on a similar
principle, but is designed to be used at a distance, for "shooting"
games, etc.

The inner workings of a light pen are quite straightforward, since it
only has to detect the electron beam, then shape the resultant pulse
to suit the input to the computer. In the early days of home computing
there were many commercial and DIY implementations of light pens, and
it may be possible to adapt one of these to suit the EJP.

The biggest issue regarding a light pen and the EJP is that of
buttons. The light pen can be used on port A, and the signal is fed
into pin six. On a joypad this line is only used for the PAUSE button,
so it would be conceivable to build a light pen supporting 20 buttons!
In practice the most likely use for a light pen would be as a mouse
replacement/complement, so any more than four buttons would be
overkill. In fact, my prototype light pen only has two buttons,
representing the left and right mouse buttons on a normal Atari mouse.

It is my proposal that anyone building a light pen should map the
buttons as follows:-

     "Left" button      =      Joypad LEFT
     "Right" button      =      Joypad RIGHT
     Button 3      =      Joypad UP
     Button 4      =      Joypad DOWN
These buttons have been selected since they make most sense, and are
all connected to one line within the joypad, reducing the time
required to read them all (i.e. all four buttons are returned as a
bitmask with one read, rather than with four reads).

If anyone writes a driver to support a light pen as a mouse (i.e.
outside of one specific program) then the notes about installing an
"EJP0" cookie should be noted, and you are advised to contact me about
the contents of the structure this should point to. In addition, such
a driver should ideally work in co-operation with the existing mouse,
and the driver should be able to "unhook" itself at the request of the
user - i.e. if they want to run a program that needs the EJPs for
something else.

9.2      Example light pen code

I do not have any example code available for this at present, though
it should be a "simple" case of reading address 0xFF9220 and 0xFF9222
for the x and y co-ordinates of the light pen respectively.

The buttons will be read in the same way as for the joypad.

There is a potential problem: according to "The Atari Compendium" only
the lower ten bits are significant, giving a range of 0-1023. Since I
have not tried any code for this, I do not know if that is in terms of
pixels, or in terms of relative distance. If it is a pixel value the
code will behave unpredictably for large (>1024 pixels) screens.

In addition the light pen relies on the timing of the video system, so
will probably be incompatible with video cards and maybe with
resolution enhancers such as Blow Up or Screenblaster. All this,
however, is pure speculation, and is simply included as a warning, or
as a possibility for courageous readers to explore (let me have the
results, though!).

9.3      Light pen circuit diagram

I have a circuit diagram for a light pen designed to work with the old
Atari 8-bit micros. I am in the middle of constructing this, although
it is temporarily on hold due to other commitments.

The design I am using was originally published in an old copy of
"Electronics - The Maplin Magazine", and was subsequently republished
in one of their compilation books. The book, unfortunately, is out of
print, although if you really want to try to build your own light pen,
you could try contacting Maplin (I got my copy from my local Maplin
shop, who had a reference copy of the book, and photocopied the
article for me).

If/when I finish my light pen, and assuming it works, I shall try to
get permission from Maplin to reproduce the circuit diagram here.

9.4      Programs which will use a light pen

None, as far as I know.

10.1      Other output devices

As has been stated before, the joypad is configured by writing to four
output lines. It is conceivable that these lines could be tapped off
for other purposes, and I believe that some of the resolution
enhancers for the Falcon rely on this trick to communicate with their

It would be possible to build a full 8-bit output port from both EJPs,
or a 4-bit output from one. If anyone builds such a device for any
useful reason, please mail me with details.

11.1      Other input devices

Similarly the EJP has a number of input lines, as well as 2 ADCs. It
could consequently be used for a number of different input devices.
For example, with both EJPs it would be possible to make a four
channel "mixer" controller for sending out MIDI continuous controller
data, or the digital inputs could be attached to footswitches for a
similar purpose. If you design any device or code to support such
devices, please mail me with full details so that I can include them

                 END OF FAQ[/code]

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