Modem directly connected to the console port.

Discussion in 'Cisco' started by AM, Dec 30, 2004.

  1. AM

    AM Guest

    I apologize for high number of questions I'm posting these days.

    I read 837's manual and it says I should use a particular cable (not the console's one) to connect an analog modem
    directly to the console port. It suggest me to contact the vendor.

    Which cable it refers to? Does anyone know the part number? Or pinouts connections?

    Thank you all,

    Alex.
     
    AM, Dec 30, 2004
    #1
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  2. "AM" <> wrote in message
    news:pLWAd.8769$...
    > I read 837's manual and it says I should use a particular cable (not the

    console's one) to connect an analog modem
    > directly to the console port. It suggest me to contact the vendor.
    >
    > Which cable it refers to? Does anyone know the part number? Or pinouts

    connections?

    It just means you need a null modem adapter (null terminal adapter?) to hook
    up a modem. The modem and terminal reverse the TX/RX, RTS/CTS and
    DTR/DSR(CD) signals. You can't just use a gender changer or 9-to-25 pin
    adapter.
     
    Phillip Remaker, Dec 30, 2004
    #2
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  3. In article <PLWAd.8769$>, AM <> wrote:
    :I read 837's manual and it says I should use a particular cable (not the console's one) to connect an analog modem
    :directly to the console port. It suggest me to contact the vendor.

    :Which cable it refers to? Does anyone know the part number? Or pinouts connections?

    The cable that you would use to connect the console to a PC would
    treat the PC as DTE (Data Transmission Equipment) and the
    console as DCE (Data Communications Equipment.)

    When you are dealing with RS-232, you must always connect a DTE to a DCE,
    never a DTE to a DTE or a DCE to a DCE.

    A modem is also DCE, as is the console, so you cannot use a regular
    cable to connect the two. Instead you must use a "cross-over"
    cable, also commonly known as a "null-modem cable". A cross-over
    cable just has to exchange some wire pairs in order for the circuit
    to work properly.

    When you find the analog modem, you will likely discover that it
    has a DB25 (25 pin) connector on it -- but the cable for to connect to your
    PC likely has a DB9 (9 pin) connector. You might also find that the
    cable to connect to the PC is the wrong "gender" to plug in to the
    modem.

    Thus, what you might need in order to make the connection is a cable
    that crosses over the correct wires, converts from 25 pin to 9 pin, and
    also switches the gender of the connector. You may be able to find
    exactly the right device at Radio Shack (Tandy) or Circuit City or
    similar store that mostly sells consumer electronics these days but
    still has a smantering of ICs held over from the days when people built
    their own circuits.

    If it turns out that all you need is the null modem part, on
    a 25 pin cable, without DB9<->DB25, then that might be the easiest
    to find, and it's fairly easy to change a straight length of cable
    to cross-over... if you have the right little tool (otherwise it's
    hard!).

    It is getting hard to find RS-232 cables, or even salesdroids who know
    what an RS-232 cable *is*. These days, especially if you need
    the DB9<->DB25 step, you might find it easiest to ask about
    "serial adapters for Palm" -- the serial adapters they sell for
    Palm handhelds do a fine job of converting DB9<->DB25, but are NOT
    cross-over, but if you can point to it and say "I want something
    that looks like that except it is male on both ends" then you would
    probably have better luck with a young sales rep than if you were
    to describe what the device has to -do-.

    I would suggest that before you go into a store, that you look
    closely at what kind of connector is on the modem, and what kind
    of connector is on the console cable, and that you *write that down*
    and take the paper with you. If you are like me, then when faced
    with a choice of cross-over devices, you will likely get confused
    about what the connections you carefully memorized were.

    The last time, a couple of months ago, that I went into a Radio Shack,
    I was able to find exactly -one- of the cross-over gender-changing
    DB9<->DB25 connectors, and that only by looking carefully four times
    in the right section; the sales people didn't have a clue what I
    was talking about, and it was easy to overlook the one package I
    needed on the wallful of random connectors and RF convertors and
    telephone jacks and so on.
    --
    "Infinity is like a stuffed walrus I can hold in the palm of my hand.
    Don't do anything with infinity you wouldn't do with a stuffed walrus."
    -- Dr. Fletcher, Va. Polytechnic Inst. and St. Univ.
     
    Walter Roberson, Dec 30, 2004
    #3
  4. AM

    AM Guest

    Walter Roberson wrote:

    > In article <PLWAd.8769$>, AM <> wrote:
    > :I read 837's manual and it says I should use a particular cable (not the console's one) to connect an analog modem
    > :directly to the console port. It suggest me to contact the vendor.
    >
    > :Which cable it refers to? Does anyone know the part number? Or pinouts connections?
    >
    > The cable that you would use to connect the console to a PC would
    > treat the PC as DTE (Data Transmission Equipment) and the
    > console as DCE (Data Communications Equipment.)
    >


    Thank you Walter and Philip, The cable you've talked about is perhaps the same used to connect 2 PCs
    via serial connection (DTE <->DTE),isn't it? I have a couple of them but both have male gender
    connector as that of the console cable furnished with 837( the other connector has an RJ45 connector).
    Hereby I must find out an DB9 adapter female/female and link the console cable and the null modem
    cable with the adapter.

    Thank you!
    Alex.
     
    AM, Dec 30, 2004
    #4
  5. In article <pv%Ad.348518$>, AM <> wrote:

    :Thank you Walter and Philip, The cable you've talked about is perhaps the same used to connect 2 PCs
    :via serial connection (DTE <->DTE),isn't it?

    Yes, that's exactly the same effect that you need. A DTE<->DTE cable
    is exactly the same as a DCE<->DCE cable.

    :I have a couple of them but both have male gender
    :connector as that of the console cable furnished with 837( the other connector has an RJ45 connector).
    :Hereby I must find out an DB9 adapter female/female and link the console cable and the null modem
    :cable with the adapter.

    Please re-check your analog modem. I have seen very few analog modems
    with DB9 connectors on them: DB25 is the usual for analog modems
    that use RS-232. Macintosh modems used mini-DIN8 connectors for a time
    (which happens to be perfect for connecting to my old SGI IRIX
    workstations), but modems for PCs never got around to adopting DB9.
    Instead, modems for PCs tended to go internal with PCI connectors instead
    of serial connectors -- so since it was largely *non*-PCs that needed
    external modems, the DB25 connector stuck. These days, external modems
    are tending towards USB connections, having skipped DB9.
    --
    I've been working on a kernel
    All the livelong night.
    I've been working on a kernel
    And it still won't work quite right. -- J. Benson & J. Doll
     
    Walter Roberson, Dec 30, 2004
    #5
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