======================================================================
Apple-II 16-Pin Game-Port to IBM-PC RS-232 (DE-9) Serial-Port Cable
by James Davis, Beagle Buddy 227; Copyright 2017, All rights reserved.
======================================================================

The purpose of this article is to show how to connect an Apple-II to
an IBM-PC RS-232 (DE-9) Serial-Port using the Apple-II 16-Pin Game-
Port connector.  Having such an interface allows the Apple-II to com-
municate directly with an IBM-PC.

This interface connects an Apple-II to an IBM-PC as if the Apple-II is
Data Communication/Circuit-Terminating Equipment (DCE) [like a MoDem].
It is NOT an Apple-II Serial-Port identical to an IBM-PC Serial-Port,
which is Data Terminal Equipment (DTE).  [But, the Apple-II is really
DTE, not DCE!  Therefore, this interface is more like a Null-MoDem
connection between two DTE devices.]  To build it requires only half
of a Serial (MoDem) cable (a pigtail) with a male plug, some electron-
ic buffering and/or line driver circuitry (currently 10 or 11 resist-
ors in a small box), and half of a 16-Pin DIP jumper-cable.

All output signals are controllable by software; except that, by use
of a jumper block (or hardwiring), the Data Carrier Detect (DCD) and
Data Set Ready (DSR) signals may be set (pulled high) via hardware
(conforming to Don Lancasters ASK THE GURU [April 1989] "A 57600 Baud
Interface", making his "57600 Baud [output] Print Driver for Apple-IIe
and IIgs" viable for this interface).  I/O-Drivers for this interface
still have to be written.


[I am hoping that some Apple-II Enthusiasts/Programmers can write
drivers for this hardware and write new Apple Disk Transfer (ADT)
{Apple-II and IBM/Windows machine-language} software to utilize it for
that purpose.  But, drivers/software to utilize it with standard
telecommunication programs would also be nice to have.  And, I would
like all this without requiring JAVA(!) or any extra programming
language or operating system beyond 6502 and IBM/Intel
machine/assembly-language, Apple ProDOS and Windows-(98se~7/64).]

Following is the schematic diagram for this interface.  It uses 470
ohm resistors as buffers for all I/O signals.  It uses 22,000 ohm
resistors and 0.1 microfarad capacitors to pull-up the Transmitted
Data (/TxD), Data Terminal Ready (DTR), and Request To Send (RTS)
inputs.  These pull-up circuits make the Apple-II, II+, IIe, & Enhanc-
ed IIe pushbutton/switch circuitry function like that of the Extended
Keyboard Apple-IIe.  Strictly speaking, they are not necessary for
this interface to work on an Extended Keyboard Apple-IIe; but having
them in parallel with those on an Extended Keyboard Apple-IIe will do
no harm.  The only disadvantage is that capacitors slow down the sig-
nal response time.  But, capacitors are also like little power cells,
giving circuits a boost when they need it most.  Using these
capacitors is optional in any case.

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Apple-II 16-Pin Game-Port to IBM-PC RS-232 (DE-9) Serial-Port Cable
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Apple-II 16-Pin Game-Port ~ IBM-PC RS-232 (DE-9) Serial-Port Schematic
======================================================================

   DE-9: (Male Plug)               Apple-II 16-Pin Game-Port (Header)
-----------------------           ------------------------------------
         [DTE]                                    [DCE]

                 +------------------------------------+
         +-------|--------------------------------+   |
         |       |        +-------------------+   |   |
         |       | JMPBLK | +-------------+   |   |   |
         |       +--O||O--+ |___          |   |   |   |
         |CTS    DSR || DCD |RxD         || || || ||
         |       +--O||O--+ |            |4| |4| |4| |4|
 CASSIN/ |       | ___ | |    *Shield |7| |7| |7| |7| <-Ohms
 CASSOUT |       +--O  O--|-|--+  Ground |0| |0| |0| |0|
   ( O )-|-------|---+----|-|--|------+  |_| |_| |_| |_|
     |RI |   +---|---|--+ | |  |    PG|   |   |   |   |   !** !** !***
     |9 |8+ |7+ |6+ | | | |  |   +--O---O---O---O---O---O---O---O--+
  ,--|---|---|---|--./  | | | ||  | 16 15- 14- 13+ 12+ 11- 10- 09+ |
 /   O   O   O   O   \  | | | |4|  | NC  AN0 AN1 AN2 AN3 GC3 GC1 SW3 |
/  O   O   O   O   O  \ | | | |7|   ]     GAME I/O   ___   (HEADER)  |
`--|---|---|---|---|-- | | | |0|  | +5V SW0 SW1 SW2 STB GC0 GC2 GND |
   |5- |4+ |3+ |2- |1  | | | |_|  |"01+ 02- 03- 04+ 05+ 06- 07- 08- |
 SG|   |   |   |   +----|-+ |  |   +--O---O---O---O---O---O---O---O--+
   |   |   |   +--------|---+  |      |   |** |** |***    !** !** |
   +---|---|------------|------|------|---|---|---|---------------+--+
       |   |___         |      |      |   |OA |SA |Shift keys        |
    DTR|   |TxD      RTS|   +--++---+-+   |   |   |           Signal |
       |   |            |   |   |   |  .1 |.1 |.1 |           Ground V
      || ||          || || || || f |f |f |
      |4| |4|          |4| |2| |2| |2|  +-+ +-+ +-+   * Pin-16 can be
      |7| |7| <-Ohms-> |7| |2| |2| |2|  | | | | | |   used as a tie-
      |0| |0|          |0| |K| |K| |K|  = | = | = |   point for a DE-9
      |_| |_|          |_| |_| |_| |_|  | | | | | |   pig-tail cable's
       |   |            |   |   |   |   V | V | V |   shield ground
       |   |            +---+---|---|-----|---+   |   wire that should
       |   +--------------------+---|-----+       |   surround all the
       +----------------------------+-------------+   twisted-pairs.

!   No Connection (NC)
**  These inputs are pulled low through capacitors on the motherboard.
*** These inputs are pulled high through resistors on the motherboard.
--- Then, all are also pulled high here!  The jumper block switches
    between hardware pullup or software control of DCD and DSR.
() Relative Polarities: [(-)=(0v)=(GND)] < [(+)=(+5v)=(VCC)]; these
    are the voltages (or "relative polarities") at the socket/plug
    when empty and power is applied (e.g., when the Apple-II "ON").

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Apple-II 16-Pin Game-Port to IBM-PC RS-232 (DE-9) Serial-Port Cable
======================================================================
Apple-II Game-Port to IBM-PC RS-232 (DE-9) Serial-Port Connector/Cable
======================================================================

Pinouts are shown as if you're looking at the end of the serial cable.
The signals are named from the Data Terminal Equipment point of view
(e.g., an IBM-PC Serial-Port).

DE-9:                         (Male Plug)
                        ,---------------------.
                        \  1   2   3   4   5  /
                         \   6   7   8   9   /
                          `-----------------

In this RS-232 (DE-9) Serial-Port to Apple-II 16-Pin Game-Port
Connect-or cable, all signals should have twisted-pair wiring; each
with one wire connected to a pin, and one wire connected to Signal
Ground (which is not connected to the Shield/Frame Ground of the DE-9
Male Plug).  [The Shield/Frame Ground propagates through the cable
from the IBM-PC side and just floats on the Apple-II side, since there
is no connection to the Apple-II chasis through the Game-Port.  Game-
Port Pin-16 can be used as an anchor point for the Shield/Frame-Wire,
since it is not con-nected to anything on the Apple-II motherboard.]

----------------------------------------------------------------------
IBM-PC RS-232 (DE-9) Serial-Port           Apple-II 16-Pin Game-Port
----------------------------------------   ---------------------------
Pin-#    DE-9   RS-232 Function      I/O   Pin-#   Game-Port Function
------   ----   -------------------- ---   -----   -------------------
     1   DCD    Data Carrier Detect  <--   *  14   Annunciator-1   ***
     2  /RxD    Received Data        <--   *  15   Annunciator-0
     3  /TxD    Transmitted Data     -->   *  02   Pushbutton-0
     4   DTR    Data Terminal Ready  -->   *  03   Pushbutton-1    ***
     5   SG     Signal Ground (0vDC) <------> 08   Ground (0vDC)
     6   DSR    Data Set Ready       <--   *  12   Annunciator-3   ***
     7   RTS    Request To Send      -->   *  04   Pushbutton-2
     8   CTS    Clear To Send        <--   *  13   Annunciator-2
     9   RI     Ring Indicator  (NC) <--   ** 01   TTL-High (+5vDC) **
------   ----   -------------------- ---   -----   -------------------
Shield   PG     Shield/Frame Ground  N/A      16   Not Connected
----------------------------------------------------------------------
Unused Apple-II Game-Port Pins: (NC) <--      05   /$C040 Strobe
                                (NC) -->      06   Game-Control-0
                                (NC) -->      07   Game-Control-2
                                (NC) -->      09   NC/GS Pushbutton-3
                                (NC) -->      10   Game-Control-1
                                (NC) -->      11   Game-Control-3
----------------------------------------------------------------------


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Apple-II 16-Pin Game-Port to IBM-PC RS-232 (DE-9) Serial-Port Cable
======================================================================

* These signals should be buffered and may need to be double inverted;
as in the Apple-II Red Book, pages 114-121, "A Simple Serial Output".
[A non-inverting octal buffer & line driver integrated circuit chip
{e.g., A 7400 or 4000 series IC} should work for all 7 I/O signals.]
Current limiting resistors (as illustrated/used above) will also work!

** TTL-High (+5vDC) [Game-Port, Pin-1] should be used to power any
buffers and/or line driver circuitry.  It should not be connected to
the IBM-PC RS-232 Ring Indicator [DE-9, Pin-9] input signal line.

[Cassette-In/Out can be used for Ring Indicator I/O signals.]
[Cassette-In can also be used as a 4th pushbutton input.]

*** Data Carrier Detect (DCD), Data Set Ready (DSR), and Data Terminal
Ready (DTR) are interconnected within a Null-MoDem Cable (see below),
so don't use one of these cables to cut in half.  Also, on the Apple-
II Game-Port side of the interface, if all signals are properly buf-
fered by the interface, no two can be shorted together by the use of a
Null-MoDem Cable; but, if signals are not buffered, then these signals
will be shorted together by the use of a Null-MoDem Cable, and that
could potentially damage your computer!

----------------------------------------------------------------------

 Rather than connecting this circuitry to a DE-9 (Male Plug) connect-
or, connecting it to a Pololu 23201a Serial Adapter will give us a
real RS-232 (DE-9) Serial-Port with all the proper voltage levels and
polar-ities.  Then, a Null-MoDem cable with DE-9 (Male Plug)
connectors on each end will be necessary to achieve the same result.
See my alter-nate article: "Apple-II 16-Pin Game-Port to RS-232 (DE-9)
Serial-Port Connector" by James Davis, Beagle Buddy 227.

Information about the Pololu 23201a Serial Adapter can be found here:

Serial Adapter Fully Assembled <https://www.pololu.com/product/126> or
<https://www.superdroidrobots.com/shop/item.aspx/pololu-23201a-serial-
adapter-fully-assembled-3-5v-ttl/1282/>

Serial Adapter Partial Kit <https://www.pololu.com/product/0127>









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Apple-II 16-Pin Game-Port to IBM-PC RS-232 (DE-9) Serial-Port Cable
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Reference: Non-Apple DE-9 Serial-Ports (RS-232 Interface Standard)
======================================================================

Following are the most common RS-232 signals and DE-9 pin assignments:

Pinouts are shown as if you're looking at the back of an IBM-PC.  The
signals are named from the Data Terminal Equipment (DTE) point of view
(e.g., an IBM-PC Serial-Port).

DE-9:                       (Female Socket)
                        ,---------------------.
                        \  5   4   3   2   1  /
                         \   9   8   7   6   /
                          `-----------------

----------------------------------------------------------------------
Pin-#    DE-9   RS-232 Function    (IBM-PC: Input/Output) [DCE<->DTE]*
------   ----   ------------------------------------------------------
Shield   PG     Shield Ground (0vDC)                (I/O) [DCE<->DTE]*
     1   DCD    Data Carrier Detect               (Input) [DCE-->DTE]*
     2  /RxD    Received Data                     (Input) [DCE-->DTE]*
     3  /TxD    Transmitted Data                 (Output) [DCE<--DTE]*
     4   DTR    Data Terminal Ready              (Output) [DCE<--DTE]*
     5   SG     Signal Ground (0vDC)                (I/O) [DCE<->DTE]*
     6   DSR    Data Set Ready                    (Input) [DCE-->DTE]*
     7   RTS    Request To Send                  (Output) [DCE<--DTE]*
     8   CTS    Clear To Send                     (Input) [DCE-->DTE]*
     9   RI     Ring Indicator                    (Input) [DCE-->DTE]*
----------------------------------------------------------------------
*  DCE - Data Communication Equipment (e.g., a MoDem)
   DTE - Data Terminal Equipment (e.g., a Computer, or a Monitor/CRT)
----------------------------------------------------------------------

Shield Ground (0vDC) [AKA, Frame/Protective Ground (FG/PG)/Shielding
(SHLD)]: Frame grounding provides an electrical connection to give
connected devices a common current path to earth (GROUND).  Shielding
protects equipment from Electrical and Magnetic Interference (EMI) and
from Radio Frequency Interference (RFI) by shunting unwanted signals
to ground before they can interfere with any communication signals.
Shielding/Frame/Protective Ground may or may not be connected to
Signal Ground (SG) inside of all equipment or devices.  [In fact, it
should not be connected so anywhere other than at the power supply.
More than one connection between Protective and Signal Grounds can
cause ground-loops which may then amplify interference instead of
eliminating it, hence defeating the main purposes of protective
grounding.  Adding shielding to all communication signals helps to
prevent this.  (Twisted-pair wiring also helps to prevent this.)]


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Apple-II 16-Pin Game-Port to IBM-PC RS-232 (DE-9) Serial-Port Cable
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Data Carrier Detect (DCD) [Input]: This signal is generated by a MoDem
(DCE) when it senses (Detects) a carrier tone on the telephone line
(or on a wireless radio/telephone carrier channel).  It tells a
computer (DTE) that a telecommunication connection to another computer
(DTE) has been made via MoDems [the local DCE is receiving a carrier
from a remote DCE] and to prepare for transmission or receipt of
demodulated serialized digital (binary) data from its MoDem (DCE).  No
other kind of Data Communication Equipment (DCE) devices need this
signal; only DCE devices that Modulate and Demodulate a carrier signal
need to detect a carrier and indicate it.  This signal is commonly
crossed over [from Data Terminal Ready (DTR)] when the connected
device is another DTE device.  [Null-MoDem cables have this crossover
wired internally; Serial/MoDem cables do not.]  [To provide an
automatic (brainless) uninterruptable DTR acknowledgment to an
incoming DSR signal, DTR may be connected directly to DSR (and perhaps
also to DCD), without going through any other circuitry.]
              ___
Receive Data (RxD) [Input]: This (negative logic) signal conveys
serial data sent from Data Communication Equipment (DCE) [via a
straight-through (Serial/MoDem) cable] or from another Data Terminal
Equipment (DTE) device [via a crossover (Null-MoDem) cable].  This
signal needs to be crossed over [from Transmit Data (/TxD)] when the
connected device is another DTE device.  [Null-MoDem cables have this
crossover wired internally; MoDem cables do not.]
               ___
Transmit Data (TxD) [Output]: This (negative logic) signal conveys
serial data sent from Data Terminal Equipment (DTE) to Data
Communication Equipment (DCE) [via a straight-through (Serial/MoDem)
cable] or to another DTE device [via a crossover (Null-MoDem) cable].
This signal needs to be crossed over [to Receive Data (/RxD)] when the
connected device is another DTE device.  [Null-MoDem cables have this
crossover wired internally; Serial/MoDem cables do not.]

Data Terminal Ready (DTR) [Output]: This signal indicates that a Data
Terminal Equipment (DTE) device is ready to go on line [Ready To
Receive (RTR), initiate, or continue a call]; and, it may also be used
for Flow Control Protocol (FCP) handshaking.  This signal needs to be
crossed over [to Data Set Ready (DSR) and to Data Carrier Detect
(DCD)] when the connected device is another DTE device.  [Null-MoDem
cables have this crossover wired internally; Serial/MoDem cables do
not.]  [To provide an automatic (brainless) uninteruptable DTR
acknowledgment to an incomming DSR signal, DTR may be connected
directly to DSR (and perhaps also to DCD), without going through any
other circuitry.]




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Apple-II 16-Pin Game-Port to IBM-PC RS-232 (DE-9) Serial-Port Cable
======================================================================

Signal Ground (SG): Provides an electrical connection to give
connected devices a common Input and Output (I/O) electric current
return path and a common electric voltage level (0vDC) that devices
can reference RS232 signals to.

Data Set Ready (DSR) [Input]: This signal indicates that a Data
Communication Equipment (DCE) device is turned on and ready to
communicate [Ready To Receive (RTR) commands or data].  This signal
needs to be crossed over [from Data Terminal Ready (DTR)] when the
connected device is another DTE device.  [Null-MoDem cables have this
crossover wired internally; Serial/MoDem cables do not.]  [To provide
an automatic (brainless) uninteruptable DTR acknowledgment to an
incomming DSR signal, DTR may be connected directly to DSR (and
perhaps also to DCD), without going through any other circuitry.]

Request To Send (RTS) or Ready To Receive (RTR) [Output]: This signal
Requests the Data Communication Equipment (DCE) prepare To Send data
to the Data Terminal Equipment (DTE) and/or tells the DCE that the DTE
is Ready To Receive (RTR) data.  This signal's primary purpose is to
control half duplex MoDems.  Printers commonly ignore this signal
(e.g., they have no wires connected to it).  This signal needs to be
crossed over [with Clear To Send (CTS)] when the connected device is
another DTE device.  [Null-MoDem cables have this crossover wired
internally; Serial/MoDem cables do not.]

Clear To Send (CTS) [Input]: This signal returns a Ready To Receive
(RTR) response to a Request To Send (RTS) signal [the DCE is ready to
accept data from the DTE].  This signal is used mostly by half duplex
MoDems.  This signal needs to be crossed over [with Request To Send
(RTS)] when the connected device is another DTE device.  [Null-MoDem
cables have this crossover wired internally; Serial/MoDem cables do
not.]

Ring Indicator (RI) [Input]: This signal is generated by a MoDem (DCE)
when it senses (Detects) a incoming ring tone/signal on the telephone
line (or on a wireless radio/telephone carrier channel).  It tells a
computer (DTE) that the telephone is ringing and needs to be answered.
This "request to connect" signal is used only by MoDems.--[Or, by
people calling other people!]

[See also: "RS-232" <https://en.wikipedia.org/w/index.php?title=RS-232
&oldid=740222779> and/or "Serial Port" <https://en.wikipedia.org/w/-
index.php?title=Serial_port&oldid=745011055> from Wikipedia, the free
encyclopedia <https://en.wikipedia.org/>.]




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Apple-II 16-Pin Game-Port to IBM-PC RS-232 (DE-9) Serial-Port Cable
======================================================================
Reference: Apple Game Port (9-pin Connector)
======================================================================

This "Game Port" is strictly an "Input Port" -- It has no Outputs!

     ,---------------------.                    Coresponding Apple-II
     \  5   4   3   2   1  /                        16-Pin DIP Socket
      \   9   8   7   6   /                                (Internal)
       `-----------------                                   Pin-#'s
                                                            ========
     Pin-1  Pushbutton-1 ................................... Pin-03
     Pin-2  Power [+5vDC (TTL high)] ....................... Pin-01
     Pin-3  Ground [0vDC (TTL low)] ........................ Pin-08
  ** Pin-4  Game-Control-2 or PDL2 (Joystick-2 X-axis) ..... Pin-07
     Pin-5  Game-Control-0 or PDL0 (Joystick-1 X-axis) ..... Pin-06
  ** Pin-6  Pushbutton-2 ................................... Pin-04
     Pin-7  Pushbutton-0 (usually the "Fire" button) ....... Pin-02
     Pin-8  Game-Control-1 or PDL1 (Joystick-1 Y-axis) ..... Pin-10
  ** Pin-9  Game-Control-3 or PDL3 (Joystick-2 Y-axis) ..... Pin-11

  ** Note: These functions are not available on the IIc or IIc+.

======================================================================
Apple Game Port (Internal 16-Pin DIP Socket)
[only on the Apple-II, II+, IIe, & IIGS motherboads]
======================================================================

All Apple-II Computers with slots have this connector internally.

This "Game Port" is an "Input Port" and an "Output Port" (also known
as an "I/O Port").  It has four analog inputs, three or four digital
inputs (three on the II, II+, or IIe; & four on the IIGS), five
digital outputs [one of which is a "Strobe" output (**)], +5vDC (TTL
high) and Ground [0vDC (TTL low)], and one or two unused pins (not
connected to anything on the motherboard; two on the II, II+, or IIe;
& one on the IIGS) that can be used as junction point terminals.

Besides its usefulness as a "Game Port" [for up to four game paddles
or two joysticks (using its analog & digital inputs)], it can also be
used as an "Octal" (3-bit) or "Nibble" (4-bit) (three on the II, II+,
or IIe; & three or four on the IIGS) "Parallel Port" (using its analog
inputs for handshaking, and its digital inputs & outputs for data and
hanshaking) (***), or (theoretically:) as up to three or four (three
on the II, II+, or IIe; & four on the IIGS) "[Universal?] Serial (1-
bit) Ports" (using its digital inputs and outputs).

*** [See: Apple Disk Transfer (AP2222PC) {zip package from Asimov.net}
     <ftp://public.asimov.net/pub/apple_II/utility/ap2222pc.zip>]

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                               Page  8
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Apple-II 16-Pin Game-Port to IBM-PC RS-232 (DE-9) Serial-Port Cable
======================================================================

                        Pin# [A/D - I/O] Pin#
                       .----.-----------.----.
Pushbutton-3 (GS only) | 09 | DI+/* -0V | 08 | Ground (0VDC)
GameCtrl-1 (Stick-1 Y) | 10 | AI-   -AI | 07 | GameCtrl-2 (Stick-2 X)
GameCtrl-3 (Stick-2 Y) | 11 | AI-   -AI | 06 | GameCtrl-0 (Stick-1 X)
         Annunciator-3 | 12 | DO+   +SO | 05 | /$C040 Strobe **
         Annunciator-2 | 13 | DO+   +DI | 04 | Pushbutton-2
         Annunciator-1 | 14 | DO-   -DI | 03 | Pushbutton-1
         Annunciator-0 | 15 | DO-   -DI | 02 | Pushbutton-0
         No Connection | 16 |*NC _ +5V | 01 | +5VDC (TTL high)
                       '----'----' '----'----'
                                  ^
                           Notch on socket
          (faces toward front of computer except on the IIgs)
                   ______
** Pin-5 = /$C040 Strobe [inverse logic] output on II, II+, IIe only;
   Pin-5 = +5V pullup on GS.     [() Relative Polarities: -0v < +5v.]

----------------------------------------------------------------------
Game Port Information (with BASIC Peek/Poke locations) obtained from
the Apple-II User's Guide, Second Edition by Lon Poole, pages 430-433;
the Apple-II Reference Manual, written by Christopher Espinosa, pages
23-25 & 100; the Apple-IIe Technical Reference Manual,  1986 Apple
Computer, Inc., pages 40-43 & 189-191; the Applesoft BASIC Programming
Reference Manual,  1978 Apple Computer, Inc., pages 90 & 134-135:
----------------------------------------------------------------------

Annunciator-0   Pin-15   Off   Poke Addrs,1   49240   -16296   $C058

Turns off game control output (annunciator) number 0.  The voltage on
Pin-15 of the game control is set to approximately 0 volts (TTL low).

----------------------------------------------------------------------

Annunciator-0   Pin-15   On    Poke Addrs,1   49241   -16295   $C059

Turns on game control output (annunciator) number 0.  The voltage on
Pin-15 of the game control is set to approximately +5 volts (TTL
high).

----------------------------------------------------------------------

The following game control annunciator output (1-bit) soft switches
follow the same rules as Annunciator-0 (repeated below) for their
respective pin assignments:



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                               Page  9
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Apple-II 16-Pin Game-Port to IBM-PC RS-232 (DE-9) Serial-Port Cable
======================================================================

Annunciator-0   Pin-15   Off   Poke Addrs,1   49240   -16296   $C058
Annunciator-0   Pin-15   On    Poke Addrs,1   49241   -16295   $C059

Annunciator-1   Pin-14   Off   Poke Addrs,1   49242   -16294   $C05A
Annunciator-1   Pin-14   On    Poke Addrs,1   49243   -16293   $C05B

Annunciator-2   Pin-13   Off   Poke Addrs,1   49244   -16292   $C05C
Annunciator-2   Pin-13   On    Poke Addrs,1   49245   -16291   $C05D

Annunciator-3   Pin-12   Off   Poke Addrs,1   49246   -16290   $C05E
Annunciator-3   Pin-12   On    Poke Addrs,1   49247   -16289   $C05F

----------------------------------------------------------------------

    Read Pushbutton-0   Pin-02   Peek Addrs   49249   -16287   $C061

When the pushbutton on game control number 0 or the open-apple key is
being pressed, the value in this location exceeds 127.  When it is not
being pressed, the value is 127 or less.  [Pushbutton-0 = Open-Apple
key; Pushbutton-1 = Solid-Apple/Option key; Pushbutton-2 = Shift keys]

----------------------------------------------------------------------

The following pushbutton soft switches follow the same rules as
Pushbutton-0 (repeated below) for their respective pin assignments:

    Read Pushbutton-0   Pin-02   Peek Addrs   49249   -16287   $C061

    Read Pushbutton-1   Pin-03   Peek Addrs   49250   -16286   $C062

    Read Pushbutton-2   Pin-04   Peek Addrs   49251   -16285   $C063

GS: Read Pushbutton-3   Pin-09   Peek Addrs   49248   -16286   $C060

----------------------------------------------------------------------

The Fourth Pushbutton Switch

The Apple-II, Apple-II Plus, and Apple-IIe, each have three Pushbutton
Switch inputs through their 16-pin Game I/O sockets.  These inputs are
located at addresses 49249 through 49251 ($C061 through $C063).
Examining the schematic diagrams in the Apple-II/II+/IIe technical
reference manuals, shows there is a fourth input available.  It is
used to test the status of the audio (cassette tape) input phone jack
(labeled "CASSETTE IN") on the rear of an Apple-II/II+/IIe.  It can
also be used as a digital input.  The address of this input is even
contiguous with the addresses above: 49248 ($C060).  [The logic on

======================================================================
                               Page 10
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Apple-II 16-Pin Game-Port to IBM-PC RS-232 (DE-9) Serial-Port Cable
======================================================================

this input is inverted compared to the other three, but this can be
handled in software.  (E.g., BASIC programmers can use "<128" for this
input when they use ">127" for the others, and Assembly language
programmers can use "BPL" instead of "BMI", or vice versa.)]  A
standard (mounted) phone jack with a single wire soldered to its
center conductor, with a phone cord plugged into this jack and into
the "CASSETTE IN" jack, can be used to connect to this input.  Game
port pin-9 can be used as a tie point for this connection.

The Apple-IIgs already has four Pushbutton Switch inputs through its
16-pin Game I/O socket.  It does not have audio (cassette tape) I/O
phone jacks, but its fouth switch input uses the same hardware address
and location (Game Port pin-9) as in the description above.  [And, it
uses normal/non-inverted logic (the contact is pulled up to +5vDC
intenally, on the Apple-IIgs motherboard/schematic).]

----------------------------------------------------------------------

    Stobe Output (**)   Pin-05   Peek Addrs   49216   -16320   $C040

Normally Pin-5 of the game control connector is +5 volts.  If you PEEK
memory location -16320, it drops to 0 volts for one-half microsecond.
POKE will trigger the strobe twice.

----------------------------------------------------------------------

The following is from pages 167-168 of the Apple-IIe Reference Manual:

"The hand-control inputs are connected to the timing inputs of an
NE558 quadruple 555-type analog timer.  Addressing $C07x sends a
signal from the 74LS154 that resets all four timers and causes their
outputs to go one (high).  A variable resistance of up to 150K ohms
connected between one of these inputs and the +5V supply controls the
charging time of one of four 0.022-microfarad capacitors.  When the
voltage on the capacitor passes a certain threshhold, the output of
the NE558 changes back to zero (low)."

"Programs can determine the setting of a variable resistor by
resetting the timers and then counting time until the selected timer
input changes from high to low.  The resulting count is proportional
to the resistance."

Basically, that is a long description of the BASIC PDL() function.

These can also be used as serial/parallel port handshaking inputs
[See: Apple Disk Transfer (AP2222PC) {zip package from Asimov.net}
<ftp://public.asimov.net/pub/apple_II/utility/ap2222pc.zip>].

======================================================================
                               Page 11
======================================================================
Apple-II 16-Pin Game-Port to IBM-PC RS-232 (DE-9) Serial-Port Cable
======================================================================

----------------------------------------------------------------------
GameCtrl Analog Inputs Reset    Poke Addrs,1   49264   -16272   $C070
----------------------------------------------------------------------
GameCtrl-0 (Stick-1 X) Pin-06   Peek Addrs     49252   -16284   $C064
GameCtrl-1 (Stick-1 Y) Pin-10   Peek Addrs     49253   -16283   $C065
GameCtrl-2 (Stick-2 X) Pin-07   Peek Addrs     49254   -16282   $C066
GameCtrl-3 (Stick-2 Y) Pin-11   Peek Addrs     49255   -16281   $C067
----------------------------------------------------------------------








































======================================================================
                               Page 12
======================================================================
Apple-II 16-Pin Game-Port to IBM-PC RS-232 (DE-9) Serial-Port Cable
======================================================================
Reference: Apple-II, II+, IIc, and IIgs Game Paddle Circuitry
======================================================================

+------------------------------------------+       +---------------+
|                556 Timer                 |       |  Game Paddle  |
|                                          |       | +5v           |
|       Textual Drawing:                   |       O--+--+   PB#   |
| +5v   James P. Davis, April 9, 2017      |       |  |  |  __|__  |
O--+                                       |       | || +--O   O--O-+
|  |    EXTERNAL CIRCUITRY:                |       | |1|        |  | |
| ||   COPYRIGHT 1977 APPLE COMPUTER INC. |       | |5|<--+   || | |
| |5|                                      |       | |0|   |   |5| | |
| |K|  +-----------------------------------O---+   | |K|   |   |7| | |
| |_|  |                                   |   |   |      |   |0| | |
|  |   |   |\    +-----------+             |   |   |  +----+   |_| | |
|  +---|---|+\   |           |             |   |   |  |         |  | |
|  |   |   |  >--O RESET     |         +---O---+   +--O---------O--+ |
|  |   +---|-/   |           |         |   |   |      |         |    |
| ||      |/    |           |       | /c  |   |     ||        |    |
| |5|            |           |       |/    |   |     |1|        |    |
| |K| Comparator | FLIP FLOP |  +--b-( NPN |   |     |0|        |    |
| |_|            |           |  |    |\    |   |     |0|        |    |
|  |       |\    |           |  |    | \e  |   |     |_|        |    |
|  +-------|+\   |         _ |  |      V   |   |      |         |    |
|  |       |  >--O SET     Q O--+      |   |   +------+         |    |
| ||  +---|-/   |           |  |      |   |         _|_        |    |
| |5|  |   |/    +-----------+  |      |   | .022 F            |    |
| |K|  |                        |      |   |         |        |    |
| |_|  |                     +--+--+   +---O----------+---------+    |
|  |   |                      \INV/    |   |          |              |
| V  |                       \ /    V  |         V             |
| GND  |                        V     GND  |         GND             |
|      |                        |          |                         |
+------O------------------------O----------+                         |
       |                        |                                    |
       +--< Trigger ($C070)     +--> Output ($C06x) <----------------+













======================================================================
                               Page 13
======================================================================
Apple-II 16-Pin Game-Port to IBM-PC RS-232 (DE-9) Serial-Port Cable
======================================================================
Reference: Apple-IIe Game Paddle Circuitry
======================================================================

+------------------------------------------+       +---------------+
|                558 Timer                 |       |  Game Paddle  |
|                                          |       | +5v           |
|       Textual Drawing:                   |       O--+--+   PB#   |
| +5v   James P. Davis, April 9, 2017      |       |  |  |  __|__  |
O--+                                       |       | || +--O   O--O-+
|  |    EXTERNAL CIRCUITRY:                |       | |1|        |  | |
| ||   COPYRIGHT 1977 APPLE COMPUTER INC. |       | |5|<--+   || | |
| |5|                                      |       | |0|   |   |5| | |
| |K|  +-----------------------------------O---+   | |K|   |   |7| | |
| |_|  |                                   |   |   |      |   |0| | |
|  |   |   |\    +-----------+             |   |   |  +----+   |_| | |
|  +---|---|+\   |           |             |   |   |  |         |  | |
|  |   |   |  >--O RESET     |         +---O---+   +--O---------O--+ |
|  |   +---|-/   |           |         |   |   |      |         |    |
| ||      |/    |           |       | /c  |  ||     |         |    |
| |5|            |           |       |/    |  |1|     |         |    |
| |K| Comparator | FLIP FLOP |  +--b-( NPN |  |0|     |         |    |
| |_|            |           |  |    |\    |  |0|     |         |    |
|  |       |\    |           |  |    | \e  |  |_|     |         |    |
|  +-------|+\   |         _ |  |      V   |   |      |         |    |
|  |       |  >--O SET     Q O--+      |   |   +------+         |    |
| ||  +---|-/   |           |  |      |   |         _|_        |    |
| |5|  |   |/    +-----------+  |      |   | .022 F            |    |
| |K|  |                        |      |   |         |        |    |
| |_|  |                     +--+--+   +---O----------+---------+    |
|  |   |                      \INV/    |   |          |              |
| V  |                       \ /    V  |         V             |
| GND  |                        V     GND  |         GND             |
|      |                        |          |                         |
+------O------------------------O----------+                         |
       |                        |                                    |
       +--< Trigger ($C070)     +--> Output ($C06x) <----------------+













======================================================================
                               Page 14
======================================================================
Apple-II 16-Pin Game-Port to IBM-PC RS-232 (DE-9) Serial-Port Cable
======================================================================
                                    Reference:
                                    ==================================
                                    Apple-II, II+, IIe, & Enhanced IIe
                                    Pushbutton/Switch Circuitry
    + -- -- -- +                    ==================================
    | J8 (DB9) |
    |          |  SW0/OAPL
    | 7 [O]---------------------------------------+
    |          |  SW1/CAPL/OPTION                 |
    | 1 [O]-----------------------------------+   |   + --- --- +
    |          |  SW2                         |   |   |         |
    | 6 [O]-------------------------------+   |   +---O         |
    |          |                          |   |   |   |         |
    + -- -- -- +                          |   +---|---O 74LS251 |
    + -- -- -- +                          |   |   |   |         |
    |   J15    |                          +---|---|---O         |
    | Game I/O |                          |   |   |   |         |
    |          |  SW0/OAPL                |   |   |   + --- --- +
    | 2 [O]-------------------------------|---|---+
    |          |  SW1/CAPL/OPTION         |   |   |
    | 3 [O]-------------------------------|---+   |   +5v
    |          |  SW2                     |   |   |   O
    | 4 [O]-------------------------------+   |   |   |
    |          |                          |   |   |  ||
    + -- -- -- +                         _|_  |   |  |1|
    + -- -- -- -- -- -- -- +  + --- +  X6     |   |  |K|
    |        SHIFT         |  | J17 |    |  |   |  |_|
    |        __|__         |  |     |     |   |   |   |
    |  +-----O   O--------------[O]-------+---|---|---+--------->
    |  |                   |  |     |         |   |   to keyboard
    | V  CAPL/OPTION     |  |     |         |   |      decoder
    | GND    __|__         |  |     |         |   |
    |     +--O   O------+-------[O]-----------+   |
    | +5v |             |  |  |     |             |
    | O---+  OAPL       |  |  |     |             |
    |     |  __|__      |  |  |     |             |
    |     +--O   O--+---|-------[O]---------------+
    |               |   |  |  |     |
    |              || || |  + --- +
    |              |4| |4| |
    |              |7| |7| |
    |              |0| |0| |   Textual Drawing:
    |              |_| |_| |   James P. Davis, April 9, 2017
    |               |   |  |
    |               +---+  |   CIRCUITRY:
    | Apple-IIe     | GND  |   COPYRIGHT 1987 APPLE COMPUTER INC.
    | Keyboard     V     |
    + -- -- -- -- -- -- -- +

======================================================================
                               Page 15
======================================================================
Apple-II 16-Pin Game-Port to IBM-PC RS-232 (DE-9) Serial-Port Cable
======================================================================
Reference:
===========================           +5v O---+---+
Apple Extended Keyboard IIe                   |   |
Pushbutton/Switch Circuitry                  || ||
===========================                  |1| |1|
                                         R48 |2| |2| R47
    + -- -- -- +                             |K| |K|
    | J8 (DB9) |                             |_| |_|
    |          |      SW0/OAPL                |   |
    | 7 [O]--------+--------------------------|---+
    |          |   |  SW1/CAPL/OPTION         |   |
    | 1 [O]--------|-------+------------------+   |   + --- --- +
    |          |   |  SW2  |                  |   |   |         |
    | 6 [O]--------|-------|-------+------+   |   +---O         |
    |          |   |       |       |      |   |   |   |         |
    + -- -- -- +   = C96   = C95   = C94  |   +---|---O 74LS251 |
    + -- -- -- +   |.1fd  |.1fd  |.1fd |   |   |   |         |
    | J15      |   +-------+-------+      +---|---|---O         |
    | Game I/O |                   | GND  |   |   |   |         |
    |          |  SW0/OAPL        V     |   |   |   + --- --- +
    | 2 [O]-------------------------------|---|---+
    |          |  SW1/CAPL/OPTION         |   |   |
    | 3 [O]-------------------------------|---+   |   +5v
    |          |  SW2                     |   |   |   O
    | 4 [O]-------------------------------+   |   |   |
    |          |                          |   |   |  ||
    + -- -- -- +                         \|/  |   |  |1|
    + -- -- -- -- -- -- -- +  + --- +  X6 +   |   |  |K|
    |        SHIFT         |  | J17 |    /|\  |   |  |_|
    |        __|__         |  |     |     |   |   |   |
    |  +-----O   O--------------[O]-------+---|---|---+--------->
    |  |                   |  |     |         |   |   to keyboard
    | V  CAPL/OPTION     |  |     |         |   |      decoder
    | GND    __|__         |  |     |         |   |
    |     +--O   O------+-------[O]-----------+   |
    | +5v |             |  |  |     |             |
    | O---+  OAPL       |  |  |     |             |
    |     |  __|__      |  |  |     |             |
    |     +--O   O--+---|-------[O]---------------+
    |               |   |  |  |     |
    |              || || |  + --- +
    | 470 Ohms --> |R| |R| |
    |              |_| |_| |   Textual Drawing:
    |               |   |  |   James P. Davis, April 9, 2017
    |               +---+  |
    | Apple-IIe     | GND  |   CIRCUITRY:
    | Keyboard     V     |   COPYRIGHT 1987 APPLE COMPUTER INC.
    + -- -- -- -- -- -- -- +

======================================================================
                               Page 16
======================================================================
Apple-II 16-Pin Game-Port to IBM-PC RS-232 (DE-9) Serial-Port Cable
======================================================================
Reference: Apple-IIc, IIc+, and IIgs Pushbutton/Switch Circuitry
======================================================================

Circuitry for the Apple-IIc, IIc+, and IIgs is radically different
from earlier models, but their Pushbutton/Switch functionality is the
same as that represented in the schematic above.

======================================================================
Reference: Serial (MoDem) Cable
======================================================================

The purpose of a Serial Cable is to permit Data Terminal Equipment
(DTE) [e.g., a Computer] to communicate with Data Communication Equip-
ment (DCE) [e.g., a MoDem] over a short distance.  This is a straight-
through cable (with a one-to-one pin-number correspondence).

Serial (MoDem) Cable/Wire-Connection Diagram:

                           (DE-9 Male Plugs)

           +--------------------------------+
           |   +----------------------------|---+
           |   |   +------------------------|---|---+
           |   |   |   +--------------------|---|---|---+
           |   |   |   |   +--+-------------|---|---|---|---+
           |   |   |   |   | Signal Ground  |   |   |   |   |
        ,--|---|---|---|---|--.          ,--|---|---|---|---|--.
        \  1   2   3   4   5  /<---+---->\  1   2   3   4   5  /
         \   6   7   8   9   /   Shield   \   6   7   8   9   /
          `--|---|---|---|--    /Frame    `--|---|---|---|--
             |   |   |   |       Ground       |   |   |   |
             +---|---|---|--------------------+   |   |   |
                 +---|---|------------------------+   |   |
                     +---|----------------------------+   |
                         +--------------------------------+

Pinouts are shown as if you're looking at the ends of the cable.

In RS-232 (DE-9) Serial-Port (Modem) Connector Cables, all signals
should have twisted-pair wiring; each with one wire connected to a
pin, and one wire connected to Signal Ground (which is not connected
to the Shield/Frame Ground on the DE-9 Male Plugs).  [The Shield/Frame
Ground propagates from one plug to the other through the MoDem Connec-
tor Cable's Shield/Wire.]





======================================================================
                               Page 17
======================================================================
Apple-II 16-Pin Game-Port to IBM-PC RS-232 (DE-9) Serial-Port Cable
======================================================================
Reference: Null-MoDem Cable
======================================================================

The purpose of a Null-MoDem Cable is to permit two Computers to commu-
nicate with each other over a short distance without a pair of MoDems
between them.

[DE-9, Pins 2 & 3; Crossover]:

To communicate between two Computers without MoDems, using RS-232 (DE-
9) Serial-Ports, the Transmitted Data (/TxD) output signal [DE-9: Pin-
3] of one Computer is connected to the Received Data (/RxD) input
signal [DE-9, Pin-2] of the other Computer (and vice versa) through a
Null-MoDem Cable.  Computers use these lines to transmit and to
receive data bits.

[DE-9, Pins 7 & 8; Crossover]:

To communicate between two Computers without MoDems, using RS-232 (DE-
9) Serial-Ports, the Request To Send (RTS) output signal [DE-9, Pin-7]
of one Computer is connected to the Clear To Send (CTS) input signal
[DE-9, Pin-8] of the other Computer (and vice versa) through a Null-
MoDem Cable.  Computers use these lines to control (clock) the flow of
data bits.  [Computers assert their Request To Send (RTS) output
signal if they are 'Ready To Receive (RTR)' data; MoDems assert their
Clear To Send (CTS) output signal when they are 'able to accept' data;
so, for our two Computers, each Computer is 'ready and able' to
'receive and accept' data from the other when they, individually,
assert RTS.]

[DE-9, Pins 1, 4, & 6; Crossover]:

To communicate between two Computers without MoDems, using RS-232 (DE-
9) Serial-Ports, the Data Terminal Ready (DTR) output signal [DE-9:
Pin-4] of one Computer is connected to the Data Set Ready (DSR) input
signal [DE-9, Pin-6] and to the Data Carrier Detect (DCD) input signal
[DE-9, Pin-1] of the other Computer (and vice versa) through a Null-
MoDem Cable.  Computers use these lines to indicate they are powered
on and connected.  [Computers assert their Data Terminal Ready (DTR)
output signal when they are powered on; MoDems assert their Data Set
Ready (DSR) output signal when they are powered on, and their Data
Carrier Detect (DCD) output signal when they are connected; so, for
our two Computers, each Computer has indication that they are powered
up and connected to the other.]

[DE-9, Pin-9; Not Connected]

As a general rule, the Ring Indicator (RI) input signal [DE-9, Pin-9]

======================================================================
                               Page 18
======================================================================
Apple-II 16-Pin Game-Port to IBM-PC RS-232 (DE-9) Serial-Port Cable
======================================================================

is not passed through a Null-MoDem connection.  [If so, the Ring Indi-
cator line, on either side of a Null-MoDem cable, can be used for any
other purpose {e.g., TTL-High (+5vDC), to power any buffer and/or line
driver circuitry that might be neeeded, or to power some other kind of
converter or adapter, like IOGEAR's RS-232 Serial-Port to USB adapter,
that might be connected to the port instead of a Null-MoDem Cable}.]

Null-Modem Cable/Wire-Connection Chart:

----------------------------------------------------------------------
Signal Name           DE-9  Pin  I/O  Pin   DE-9  Signal Name
-------------------   ---   ---  ---  ---   ---   --------------------
Transmit Data        /TxD    3   -->   2   /RxD   Receive Data
Receive Data         /RxD    2   <--   3   /TxD   Transmit Data
Request To Send       RTS    7   -->   8    CTS   Clear To Send
Clear To Send         CTS    8   <--   7    RTS   Request To Send
Signal Ground         SG     5   <->   5    SG    Signal Ground
Data Set Ready        DSR    6   <-+   4    DTR   Data Terminal Ready
Data Carrier Detect   DCD    1   <-+   4    DTR   Data Terminal Ready
Data Terminal Ready   DTR    4   +->   1    DCD   Data Carrier Detect
Data Terminal Ready   DTR    4   +->   6    DSR   Data Set Ready
-------------------   ---   ---  ---  ---   ---   --------------------
Shield/Frame Ground   FG    N/A  <->  N/A   FG    Shield/Frame Ground
----------------------------------------------------------------------

Null-Modem Cable/Wire-Connection Diagram:

                           (DE-9 Male Plugs)

     +-----+--------------------------------------------+
     |     |   +------------------------------------+   |
     |     |   |   +----------------------------+   |   |
     |     |   |   |   +--------------+-----+   |   |   |
     |     |   |   |   |   +--+-------|-----|---|---|---|---+
     |     |   |   |   |   | Signal Ground  |   |   |   |   |
     |  ,--|---|---|---|---|--.       |  ,--|---|---|---|---|--.
     |  \  1   2   3   4   5  /<-+----|->\  1   2   3   4   5  /
     |   \   6   7   8   9   / Shield |   \   6   7   8   9   /
     |    `--|---|---|---|--  /Frame |    `--|---|---|---|--
     |       |   |   |   NC    Ground |       |   |   |   NC
     +-------+   |   |                +-------+   |   |
                 |   +----------------------------+   |
                 +------------------------------------+

Pinouts are shown as if you're looking at the ends of the cable.



======================================================================
                               Page 19
======================================================================
Apple-II 16-Pin Game-Port to IBM-PC RS-232 (DE-9) Serial-Port Cable
======================================================================

In RS-232 (DE-9) Serial-Port Null-Modem Connector Cables, all signals
should have twisted-pair wiring; each with one wire connected to a
pin, and one wire connected to Signal Ground (which is not connected
to the Shield/Frame Ground on either of the DE-9 Male Plugs).  [The
Shield/Frame Ground propagates from one plug to the other through the
Null-MoDem Connector Cable's Shield/Wire.]

======================================================================
Simplest Apple-II 16-Pin Game-Port to IBM-PC RS-232 Serial Connections
======================================================================

Connect an Apple II to an IBM-PC Serial-Port, like this:

----------------------------------------------------------------------
           Apple II Connection                 IBM-PC Connection
-----------------------------------------    ----------------------
Game-Port   Signal (I/O)      Circuitry      DB-25   Signal   DE-9
---------   ------ -------- -------------    ------  ------   -----

01+   +5V   VCC    (TTL-H) <--+ +5vDC        <--(No Connection)--<<
            ___               |  ______                ___
02-   Sw0   RxD    (Input) <--+-|470ohm|---< Pin 2 --- TxD --- Pin 3
                              |  
                              = .1 f
                              |
08-   GND   SG     (Ground) <-+------------> Pin 7 --- SG  --- Pin 5
                   (TTL-L)      -0vDC
            ___                  ______                ___
15-   AN0   TxD    (Output) >---|470ohm|---> Pin 3 --- RxD --- Pin 2
                                 

                                       +---- Pin 4 --- RTS --- Pin 7
                                       |
                                       +---- Pin 5 --- CTS --- Pin 8

                                       +---- Pin 6 --- DSR --- Pin 6
                                       |
                                       +---- Pin 8 --- DCD --- Pin 1
                                       |
                                       +---- Pin 20 -- DTR --- Pin 4

----------------------------------------------------------------------

On the PC side, you should short together (separately, in two groups):
pins 4 & 5, and pins 6 & 8 & 20 if you are using a DB-25 connector;
or: pins 7 & 8, and pins 1 & 4 & 6 if you are using a DE-9 connector.


======================================================================
                               Page 20
======================================================================
Apple-II 16-Pin Game-Port to IBM-PC RS-232 (DE-9) Serial-Port Cable
======================================================================
Reference: Non-Apple DB-25 Serial Ports (RS-232 Interface Standard)
======================================================================

Pinouts are shown as if you're looking at the back of an IBM-PC.
The signals are named from the Data Terminal Equipment point of view
(e.g., an IBM-PC Serial-Port).

       ,------------------------------------------------------.
DB-25  \  13  12  11  10  09  08  07  06  05  04  03  02  01  /
        \   25  24  23  22  21  20  19  18  17  16  15  14   /
         `--------------------------------------------------

----------------------------------------------------------------------
Pin-#    DB-25        Function
------   -----------  ------------------------------------------------
Shield   Gnd          Protective Ground (0DCV)
     1   Gnd          Ground (0DCV)
     2   TxD          Transmitted Data (Out)
     3   RxD          Received Data (In)
     4   RTS          Request To Send
     5   CTS          Clear To Send
     6   DSR          Data Set Ready
     7   SG           Signal Ground (0DCV)
     8   DCD          Data Carrier Detect
     9   +DCV         Positive DC Test Voltage
    10   -DCV         Negative DC Test Voltage [DCE->DTE]*
    11   QM           Equalizer Mode
    12   (S)DCD       Secondary Data Carrier Detect
    13   (S)CTS       Secondary Clear To Send
    14   (S)TD, NS    Secondary Transmitted Data, or New Sync, or
                      Fault on IW1
    15   TC           Transmitter Clock [DCE->DTE]
    16   (S)RD, DCT   Secondary Received Data, or
                      Divided Clock Transmitter
    17   RC           Receiver Clock
    18   DCR          Divided Clock Receiver
    19   (S)RTS       Secondary Request To Send
    20   DTR          Data Terminal Ready
    21   SQ           Signal Quality Detect
    22   RI           Ring Indicator
    23                Data Rate Selector [Bidirectional]
    24   (TC)         Ext. Transmitter Clock [DTE->DCE]
    25                Busy
----------------------------------------------------------------------
  * DCE - Data Communications Equipment (e.g. a MoDem)
  * DTE - Data Terminal Equipment (e.g. a Monitor/CRT)
----------------------------------------------------------------------


======================================================================
                               Page 21
