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Keyboard --> RJ-11

Discussion in 'Electronic Basics' started by Luke Albers, Nov 28, 2003.

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  1. Luke Albers

    Luke Albers Guest

    Hey everyone

    I got a dummy terminal the other weekend, and the keyboard connector is
    RJ-11 on it. I am trying to figure out how to replace the PS-2 or AT
    connector on a keyboard with an RJ11 end.

    The keyboard uses a four wire electrical interface that appears as below
    when viewed from the end of the keyboard cable.


    | 1 2 3 4 |

    +--+ +--+


    1) Rxd (Data to keyboard)

    2) Gnd

    3) +12v

    4) Txd (Data from keyboard)

    Here is a link to the pinouts of the kbd connectors:

    A friend of mine has a connector to plug in his ps/2 keyboard to a RJ11
    adaptor,and it is a real simple thing. no electronics, just wires. I would
    rather use an AT keyboard, and I see that pin 3 is not used, but I don't
    really know where each of the other four wires goes in an RJ11 connector

    I appreciate any help I can get
  2. | 1) Rxd (Data to keyboard)

    | 2) Gnd

    | 3) +12v

    | 4) Txd (Data from keyboard)

    | Here is a link to the pinouts of the kbd connectors:

    It should be fairly intuitive but your keyboard will not work with this
    terminal. PS/2 keyboards run on 5 volts and your terminal is supplying 12
    meaning you'll burn out the keyboard the moment you plug it in.

    Keeping this in mind, the signal level requirements may be different
    between the devices. The PS/2 keyboard uses TTL level signals (0 and 5
    volts). It looks like the terminal may use stanard serial level comms
    which is something completely different.

    You could build an interface provided both units are speaking the same
    protocols. In that case, you'd have to make an opto-isolator circuit plus
    a voltage regulator to reduce the 12 volts to 5 for the keyboard. Your
    pin 4 is receiving data so it would go to pin 2 on the AT connector and
    the transmitting pin is pin 1 which the closest analogue on the AT
    connector is the clock.

    This is where things get different. The PS/2 and AT keyboards use a
    synchronous serial connection. The computer clocks the keyboard and the
    keyboard shifts data out the data pin. But, at the same time, the
    keyboard can _read_ data from the data pin which the computer sent to it.
    So, the data pin is actually bi-directional. The clock is just a clock.
    However, it looks like the terminal's keyboard is a real serial device
    which follows along with the rest of the terminal since it's an all
    serial device. It's more than likely receiving commands or a pulse stream
    on the receive pin and transmits data on the transmit pin. So there's no
    bidirectional communication over a single wire like the PS/2 keyboard.
  3. Gary Tait

    Gary Tait Guest

    Don't bother. It is higly unlikely the protocol is PS/2.
  4. <snip>

    Just because the terminal has a modular connector does NOT mean
    that a standard PC keyboard will work with it. In fact, it is not at all
    common for dumb terminals to have the same keyboard protocol and
    interface as a PC.

    You need to check with the terminal manufacturer, otherwise you
    run a very high risk of blowing a circuit or three.

    Dr. Anton Squeegee, Director, Dutch Surrealist Plumbing Institute
    (Known to some as Bruce Lane, KC7GR)
    kyrrin a/t bluefeathertech d-o=t c&o&m
    Motorola Radio Programming & Service Available -
    "Quando Omni Flunkus Moritati" (Red Green)

  5. Well Luke,

    A PC/AT/ps2 keyboard eats 5V. You will sure blow it when you feed it 12.

    You did not tell what type of terminal you got. Most of the ones I know used
    a kind of ASCII on a serial connection. If you still have the keyboard, you
    best use it. If that's not an option (p.e. due to mechanical ruins) you may
    nevertheless check the signals with a scope and build a converter. Which
    requires a voltage regulator and a microcontroller..... You'd prefer a type
    with a UART inside.

  6. Luke Albers

    Luke Albers Guest

    Ok I think that my friend gave me the wrong pin diagram. The terminal
    is an IBM 3153. I found another diagram that showed 5 pins, and it
    ran off 5 V, and there was only one wire for data. I will have to
    find the link again, but I think that my RJ-11 connectors only have 4
    conductors (i hear some have 6 and are still called RJ11). I will
    post the pinout that I found ASAP
  7. Luke Albers

    Luke Albers Guest

    RJ11 Plug Pin Assignments

    1 = KBD Clock
    2 = KBD Data
    +-----------+ 3 = No Connection
    |1 2 3 4 5 6| 4 = Signal Ground
    |. . . . . .| 5 = +5 Volts
    +---+---+---+ 6 = No Connection
    View = looking at plug.

    OK I think that this is something that I can work with. Anyone know
    how I could connect an AT keyboard?
  8. Gary Tait

    Gary Tait Guest

    In that case, you COULD connect the PS/2 data and clock signals to the
    clock and data signals of the tremina, not saying it will work though.
  9. Luke,

    You find the pinouts of an AT keyboard below. FAIK the XT keyboard had the
    same 5 pin DIN connector and the same pinout but a different protocol. The
    XT also used the reset pin, the AT did not. I still have an XT keyboard
    equiped the modulair connector you mentioned but I did not check the pinout.

    BTW The RJxx notation comes from the telco environment. It has to do with
    pin identities and functions, not with pin positions or contact count.
    Outside this specific environment, the RJxx notation is meaningless and
    gives a lot of confusion.


    Male End PIN SIGNAL
    Female End
    1 ---------------------------------- KBDCLK (clock)
    1 3 2 ---------------------------------- KBDAT (data)
    3 1
    4 5 3 ---------------------------------- KBRST (reset,not
    used) 5 4
    2 4 ---------------------------------- GND
    5 ---------------------------------- VCC (+5V)

    Male End PIN SIGNAL

    5 H 6 1 -------------------------------- KBDAT (data)
    3 4 2 -------------------------------- not used
    1 2 3 -------------------------------- GND
    4 -------------------------------- VCC (+5v)
    5 -------------------------------- KBCLK (clock)
    6 -------------------------------- not used

  10. If it's something well-known like a DEC or IBM terminal, it might be
    worthwhile to look on ebay for a matching keyboard.
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