# CD32 Keyboard to Serial Interface 2

    Date: Thu, 20 Oct 1994 11:07:00 +0100
    From: Klaus_Hegemann@punk.fido.de (Klaus Hegemann)
    Subject: Re: Using Auxiliary Port as Serial Port
    Message-ID: <b1990b05%fidonet@p29.f113.n2452.z2.fidonet.org>
    References: <8df67bba@coyote.dres.dnd.ca>
    Newsgroups: comp.sys.amiga.cd32
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    Hi Stan !
     s> I understand that you can use the auxiliary port (keyboard) as an
     s> RS-232 port and that this is what sernet does.  But when I look at
     s> the pinout, there is only clock and data signals, not ser-in and
     s> ser_out.  What am I missing here?
    Well, I think you refer to the A4000's kb.jack pinout. It's 'almost'
    the same as you can find at the cd32. But the difference is, tataa..:
    on the cd32 there are additional serial-interface-signals connected
    to the AUX-jack. You can find them at the former unused pins.
    The mess is, that the (serial-) signals carry [negated] TTL-level.
    As a result, you have to make sure that there is a level-conversion
    before you connect them to other computers. Without you surely kill
    your cd32.
    The cd32-FAQ shows a rather complex (but quite correct) way to do this.
    (Aehm, the level-conv., of course ;-)
    If you plan to connect the CD32 with other Amigas then I found out a
    rather easyer/cheaper way to solve that:
    Amiga                    |\ |                         Amiga CD32
                 TxD o-------| >|---.
    level: RS232             |/ |   |                     level: /TTL
    -12V..+12V            D1        |                     0V..+5V
                                   .-.
                                   | |
                                   | |        IC1
                                 R1| |   ''''''''
                                   `-'   '  _   '
                                    |    ' | \  '
                                    *------|  O-------->o /RxD Pin6
                                    |    ' |_/  '
                                   .-.   '      '
                                   | |   '      '
                                   | |   '      '
                                 R2| |   '      '
                                   `-'   '      '
                                    |    '      '
                                    |    '      '
                                    |    '      '
                                   ===   '      '
                                   ///   '   _  '
                                         '  / | '
                  RxD o<-------------------O  |---------o /TxD Pin2
                                         '  \_| '
                                         '      '
                                         ''''''''

                  GND o-----------------------*---------o GND
                                              |
                                         '''''|''
                                         ' o  o '
                                         ' |7 14'
                                         ''|''''' IC1
                                           |
                  +5V o--------------------'
    the pros. and cons.  ([1]this solution ./. [2]max232-sol. (->FAQ) )

    pros.[1]:  easy to solder
               cheap
               fits within a SUB-D 25 plug
               does not consume CD32 +5V power ;-)

    cons: 'dirty' solution; i.e. circuitry makes use of the 1488/89 tolerances
          you may only connect Amiga-computers to your cd32 when using THIS
          [1] circuitry - since they all use the 1488/89 chip set.
          PCs 'may' work, too. But interface board must contain 1488/89 chip
          set.
          I do believe that this will work on all Amigas -I tested it at least
          on 3 different Amiga-models, however, there is still no guarantee
          that this will work on yours.

    However, I use both interface-types since about 6 months.  There has
    been no problem yet.

     s> Also, has anyone made their own connector to the expansion port to
     s> pull off the RGB signals?  I'd appreciate hearing of your experience.

    Yea, does work fine.  In use for about 6 months; and still no probs, too.
    For details refer to the cd32-faq.

    I am not quite sure about the cd32-pin numbers, just take a look in the
    faq.

    bis den bald
    Klaus

    [---------------------------------------------------------------------------]
    Date: Fri, 21 Oct 1994 14:55:00 +0100
    From: Klaus_Hegemann@punk.fido.de (Klaus Hegemann)
    Subject: Re: [2]Using Auxiliary Port as Serial Port
    Message-ID: <b1a112f9%fidonet@p29.f113.n2452.z2.fidonet.org>
    References: <b1990b05%fidonet@p29.f113.n2452.z2.fidonet.org>
    Newsgroups: comp.sys.amiga.cd32
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    X-FTN-Domain: Z242@fidode
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    Hi!

    'updated info:'
           Amiga 500,2000,1200,...

           level: RS232
           -12V..+12V

                              |\ |                         Amiga CD32
                  TxD o-------| >|---.
                  Pin2        |/ |   |                     level: /TTL
                           D1        |                     0V..+5V
                           1N4001   .-.
                                    | |
                                    | |        IC1 7400
                                 R1 | |   ........
                                (*) `-'  1:  _   :
                                     |   ___| \  :3
                                     *--*___|  O-------->o /RxD Pin6
                                     |    : |_/  :
                                    .-.  2:      :
                                    | |   :      :
                                    | |   :      :
                                 R2 | |   :      :
                                (*) `-'   :      :
                                     |    :      :
                                     |    :      :
                                     |    :      :
                                    ===   :      :
                                GND ///   :   _  :4
                                         6:  / |____
                   RxD o<-------------------O  |____*----o /TxD Pin2
                   Pin3                   :  \_|
                                          :      :5
                                          :.......

                   GND o---------------*-----------------o GND Pin3
                   Pin7                |
                                       |  ........
                                       | 7:      :IC1
                                       *--:GND   :
                                       | 9:      :
                                       *--: \    :
                                       |10: |not :
                                       *--: |used:
                                       |12: |    :
                                       *--: |    :
                                       |13: |    :14
                                       `--: / +5V:-.
                                          :......: |
                                                   |
                                                   |
                   +5V o---------------------------'
                   Pin4

                shield o=======================! [n.c.] o shield
                   Pin1

    The RS232-TxD-signal carries +12V or -12V level. As the first step
    in conversion the diode D1 blocks if the signal drops to -12V.
    In this case the voltage divider (R1,R2) is only connected with
    GND potential. So the gate input carries GND level, too.
    When the RS232-TxD-signal changes to +12V the diode will pass it
    through and the voltage divider now provides a +5V-level signal to
    the gate input.
    The backward conversion consists of simple negation of the cd32's
    /TxD signal. In fact there is no level conversion.
    While the conversion for the received signal does
    work proper with any RS232 opponent, the sended
    signal furthermore carries TTL-level.
    The opponent hardware tries to regain the TTL-level signal from
    its 'RS232' input. The conversion unit handles the provided
    pseudo RS232-type signals correct (as we want ist to be:-).
    (*) voltage divider R1-R2:

       U                      U      = 12V    U   = 5V
        R1+R2     R1+R2        R1+R2           R2
       ------  =  -----
       U            R2
        R2

                                   U
                                    R1+R2
       I      = 5 mA  ==> R1+R2 = ------   = 2400 Ohm
        R1+R2                      I
                                    R1+R2

                         (R1+R2) * U
                                    R2
       U   = 5V ==> R2 = -------------  = 1000 Ohm; R1= 1400 Ohm
        R2                  U
                             R1+R2

    R1=1500 Ohm
    R2=1000 Ohm ==> I=4.8 mA ==> U(R2)=4.8 V   ..  will be OK

    IC1 = 74LS00  (4 NAND gates)
    D1 = e.g. 1N4001
    have fun !
    be careful; I am in no way responsible for any damage that may result.
    CU
    bis den bald
    Klaus                    klausi@punk.fido.de

Contributor: | Joakim Ögren

Source: | CD32 keyboard port info usenet posting by Klaus Hegemann

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Document last modified: 2002-01-10