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So many connectors -- ever wonder how to hook something up?  First, there was the DB-25.  Then the DB-9, Digital created the MMJ, someone else created the RJ-45, and so on.  Meanwhile, the world moved its networks from coaxial cable to 10Base-T, which uses Cat 5 wire and RJ-45's (hey, Ethernet is serial, right?).  There's ISDN and FDDI, too -- don't assume that all RJ-45's are 10Base-T.  Heck, ISDN even carries 90 volts, so be careful! In the following, "plug" and "male" are equivalent, as are "socket" and "female".

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Page Map
DB-15 (AUI)
DB-9 Token Ring
V.35 (X.25)

DB-9 Female
DB-25 Female
DB-25 Male


Intermec 9154

Network Straight-Through

Network Crossover

FDDI Crossover

DECserver to Cisco Router

Flowpoint Router

Alcatel-Lucent router 7750 with Cisco 3500 switch


Need to buy a DEC adapter?  Click here for the MMJ Adapters sales page!


Cat 5 Cable

The following colors are standard.  If your cable doesn't have these, you're on your own.

    White / Blue
    White / Green
    White / Brown
    White / Orange

MMJ Cable
The standard MMJ cable has six wires, and is flat, not round.

Connector Numbering.

DB-9 and DB-25 Connectors
DB-9's and DB-25's (at least the ones you buy at Radio Shack) have little numbers beside each hole.  If yours don't have numbers, here's the key.  These views are from the back of the connector.

      Female              Male
------------- -------------
\ 1 2 3 4 5 / \ 5 4 3 2 1 /
\ 6 7 8 9 / \ 9 8 7 6 /
--------- ---------

Other DB connectors use the same scheme.

DB-15 Connector
DB-15 connectors are used as network connectors known as as AUI or MAU ports. Older systems referred to them as ThickWire Ethernet ports, since the old vampire taps used them.  They are still widely seen on equipment, and transceiver modules are available to convert them to 10Base-T (RJ-45) networks.  One such module is the CentreCOM 210TS.

RJ-45, RJ-11, and MMJ Connectors
How are those phone-style plugs (RJ-45, MMJ) numbered?

Look into the socket.  Twist around so that the little plastic clip is pointing down (towards your chin).  The leftmost position is 1.

When you insert wire into a plug, make sure the clip is down.  Holding the connector so that it's pointing away from you, the leftmost position is 1.


DB-25 and DB-9
The worldwide standard (sort of) is the DB-25.  Everyone calls this RS-232, but that name's been replaced by an EIA number that nobody uses.  Warning:  There are lots of pins in a DB-25 that are used for all sorts of obscure functions.  Don't assume that "no connection" means "no function".

Male connectors are usually used on PC's.  Female connectors are usually used on modems.  Usually.

Here's what the commonly used pins mean in a DB-25:

    1    GND    (Protective ground, almost never used)
    2    TXD    (Transmit data)
    3    RXD    (Receive data)
    4    RTS    (Request to send)
    5    CTS    (Cleared to send)
    6    DSR    (Data Set ready)
    7    GND    (signal ground)
    8    DCD    (Data carrier detect)
   20    DTR    (Data terminal ready)
   22    RI     (Ring indicator)

DB-9's are simpler.  They are not used for weird stuff (usually).  The DB-9 "standard" was developed by IBM because they wanted to save money -- DB-25's are bigger, and so more expensive.  Here are the pinouts:

    1    DCD    (Data carrier detect)
    2    RXD    (Receive data)
    3    TXD    (Transmit data)
    4    DTR    (Data terminal ready)
    5    GND    (Signal ground)
    6    DSR    (Data set ready)
    7    RTS    (Request to send)
    8    CTS    (Cleared to send)
    9    RI     (Ring indicator)

Note:  The pinouts for early MicroVAX systems do not follow this scheme.  See the VMS FAQ for details.

Warning:  Token Ring networks also use DB-9's, but are definitely not serial!

RJ-45 -- Serial
Lots of equipment uses RJ-45's for serial connections.  They're cheaper than DB-25's and DB-9's, and are a lot easier to mount on a panel.  Here are the pinouts for the DECserver series of terminal servers.  DEC called this the "MJ8" connector.  Your mileage may vary with other devices.

    1    RX-    (Receive ground)
    2    RX+    (Receive data)
    3    RX-    (Transmit ground)
    4    CTS    (Cleared to send)
    5    RTS    (Request to send)
    6    TX     (Transmit data)
    7    DTR    (Data terminal ready)
    8    DSR    (Data set ready)

Note that the transmit and receive data are actually differential line drive, instead of voltages.  This is known as EIA-423.

Cisco routers have a different scheme (thanks to Jim Azbell):

    1    RTS    (Request to send)
    2    DTR    (Data terminal ready)
    3    TXD    (Transmit data)
    4    GND    (Signal ground)
    5    GND    (Signal ground)
    6    RXD    (Receive data)
    7    DSR    (Data set ready)
    8    CTS    (Cleared to send)

Note that these lines are driven against ground, not differential like the DECservers.   The Cisco documentation says that pins 1 and 8 are connected in their standard cable.

FlowPoint router console ports have yet another scheme (flowpoint.pdf):

    1    RX    (Receive data)
    2    RTS   (Request to send)
    3    N/C   (no connection)
    4    TX    (Transmit data)
    5    GND   (Ground)
    6    CTS   (Cleared to send)
    7    N/C   (no connection)
    8    N/C   (no connection)

Here's an Alcatel-Lucent router 7750 with Cisco 3500 switch, provided by Sergio Antonio.  I haven't tested this combination.

    RJ-45          DB-9
    1   RTS        8   CTS
    2   N/C        6   DSR
    3   TxD        2   RxD
    4   GND        5   GND
    5   GND        5   GND
    6   RxD        3   TxD
    7   N/C        4   DTR
    8   CTS        7   RTS

RJ-45 -- 10Base-T
RJ-45's are also used for network connections.  The most common 10Base-T scheme is known as TIA/EIA T568B, which is:

    Pin    Function
      1    Receive
      2    Receive
      3    Transmit
      4    unused
      5    unused
      6    Transmit
      7    unused
      8    unused

There are applications specified for ISDN, analog voice, IEEE 802.5/Token Ring, and other stuff.  I found a useful information in OPEN DECconnect System Overview, figure 2-2 and table 2-3.

DB-15 -- Ethernet
The AUI (MAU, ThickWire) DB-15 connectors have the following pinouts.  (This is from a document that used to be on the Ericsson web site)

    Pin    Name    Function
      1            Shield
      2    ACOL+   Collision presence
      3    ATX+    Transmission
      4    GND     Ground
      5    ARX-    Reception
      6    GND     Power return
      7    CTL+    Control output
      8    GND     Ground
      9    ACOL-   Collision presence
     10    ATX-    Transmission
     11    GND     Ground
     12    ARX-    Reception
     13    +12VDC  Power
     14    GND     Ground
     15    CTL-    Control output

The DEC Ethernet loopback connector 12-22196-02 has the following connections (from the DECstation 5000 hardware guide)

    Pins 3 and 5     Connected through a capacitor
    Pins 10 and 12   Connected through a capacitor
    Pins 13 and 6    Connected through a resistor and LED

DEC made a series of cables, known as BNE4C, followed by the length in meters.  For example, the BNE4C-2 is 2 meters long.  It has a DB-15 male connector on one end, and a DB-15 female connector on the other.  Think about it being an "extension cord" for AUI.  The information I got off Amazon says:

AUI (Attaachment Unit Interface) Transceiver cable for connnecting MAU (Medium Attachement Units) to a MAC (Medi Access Control) commonly found on 10BASE-5 (thicknet) and 10BASE-2 (thinnet) networking systems. Pinouts 3 - DO-A, Data Out Circuit A 10 - DO-B, Data Out Circuit B 11 - DO-S, Data Out Circuit Shield (not used) 5 - DI-A, Data In Circuit A 12 - DI-B, Data In Circuit B 4 - DI-S, Data In Circuit Shield 7 - CO-A, Control Out Circuit A (not used) 15 - CO-B, Control Out Circuit B (not used) 8 - CO-S, Control Out Circuit Shield (not used) 2 - CI-A, Control In Circuit A 9 - CI-B, Control In Circuit B 1 - CI-S, Control In Circuit Shield 6 - VC, Voltage Common 13 - VP, Voltage Plus (+12V) 14 - VS, Voltage Shield (not used) Shell - PG, Protective Groun.

DB-9 -- Token-Ring
The AUI (MAU, ThickWire) DB-15 connectors have the following pinouts.  (This is from a document that used to be on the Ericsson web site)

    Pin    Name        Function
      1    Receive-    Data in
      2                Frame ground
      5    Transmit-   Data out
      6    Receive+    Data in
      7                Frame ground
      8                Frame ground
      9    Transmit+   Data out

A loopback connector can be created with the following connections:

    Pins 1 and 5   Connected
    Pins 6 and 9   Connected

V.35  Pinouts
Another connector you might encounter is a 34-pin rectangular connector.  This is a CCITT V.35 (ISO 2593) connector.  Frequently used for X.25 networking.

The male connector has the following pinouts:

    Pin         Name      Function
    H            DTR        Data terminal ready
    P            TXA        Transmit data A
    S            TXB        Transmit data B
    U           SCTEA    Serial clock transmit external A
    W          SCTEB    Serial clock transmit external B
    C           RTS         Request to send
    E           DSR         Data set ready
    R           RXA        Receive data A
    T           RXB         Receive data B
    V          SCRA       Serial clock receive A
    X          SCRB       Serial clock receive B
    Y          SCTA       Serial clock transmit A
    AA       SCTB       Serial clock transmit B
    A          Shield        Frame ground or shield
    B          SG            Signal ground
    D          CTS          Clear to send
    F           DCD        Data carrier detect
    J            RI            Ring indicator

DEC Adapters
There are all sorts of useful adapter modules that were made by Digital Equipment Corporation.  The wiring diagrams are here.  A table of them are in the VMS FAQ.

Need to buy a DEC adapter?  Click here for the MMJ Adapters sales page!

Digital created the MMJ connector.  You can recognize it because the plastic clip is not in the center.  It was a great idea -- the connections are simple, but no one else adopted the idea.  The pinouts:

    1    DTR    (Data terminal ready)
    2    TX+    (Transmit data)
    3    TX-    (Transmit ground)
    4    RX-    (Receive ground)
    5    RX+    (Receive data)
    6    DSR    (Data set ready)

MMJ's use differential drive, just like RJ-45's.  Funny enough, the RJ-45 to MMJ cable is the hardest to build...

MMJ ends and crimpers are hard to find.  After hours of searching, I found that Ideal Industries sells them.  The crimper is product 30-497, and a bag of 100 MMJ ends for round cable (Cat 5 is round) is product 86-393.  I got mine at Michaels Electrical Supply (http://www.michaelselectric.com).  Costs about $100 total.

Now, how do you make it play?  I have actually tested most of these configurations.  All you need is a large spool of Cat 5 wire, appropriate crimpers and ends, and endless time.  Enjoy!

10Base-T straight through cable
The "straight through" cable is used to connect a network device (LAN card, etc.) to a hub or switch.  This cable has TIA/EIA T568B connectors on each end (hey, they look like RJ-45's to me!).  Each connector is wired like this:

    Pin    Wire
      1    White / orange
      2    Orange
      3    White / green
      4    Blue
      5    White / blue
      6    Green
      7    White / brown
      8    Brown

10Base-T crossover cable
This cable is used to connect two identical devices.  You can connect two LAN cards together to create a miniature network.  Or you can connect two hubs together to expand your network.  Technically, one connector is TIA/EIA T568B, and the other is TIA/EIA T568A.  Take a look:

    Connector 1          Connector 2
    Pin    Wire                    Pin    Wire
      1    White / orange            1    White / green
      2    Orange                    2    Green
      3    White / green             3    White / orange
      4    Blue                      4    Blue
      5    White / blue              5    White / blue
      6    Green                     6    Orange
      7    White / brown             7    White / brown
      8    Brown                     8    Brown

When I make one of these, I use a red Sharpie marker and put a band near each end so I won't confuse it with a straight through cable.  Your mileage may vary.

FDDI crossover cable
Wait, I thought FDDI used fiber!  Well, yes, but there's a version of FDDI that uses UTP -- which is good old Cat 5 cable with RJ-45's.  It's also known as CDDI, or "FDDI over copper".  The only reason you'd need a crossover cable is because you're connecting two FDDI cards together.  I had to do this, so just in case you need to know:

    Connector 1                   Connector 2
    Pin    Wire             Function        Pin  Wire
      1    White / orange   Tx+               1    White / brown
      2    Orange           Tx-               2    Brown
      3    White / green                      3    White / green
      4    Blue                               4    Blue
      5    White / blue                       5    White / blue
      6    Green                              6    Green
      7    White / brown    Rx+               7    White / orange
      8    Brown            Rx-               8    Orange

The colors used here are not standardized as they are for 10Base-T.  I just used the 10Base-T standard for the first connector.  FDDI requires that the outside two pairs are swapped, but the other pairs are straight through.  The good thing about standards is there are so many to choose from!

It seems every piece of Digital equipment has at least one MMJ connector.  Here's how to make a "straight through" MMJ cable.  The colors are my own choice.

    1 Orange               1 White / orange
    2 Blue                 2 Green
    3 White / blue         3 White / green
    4 White / green        4 White / blue
    5 Green                5 Blue
    6 White / orange       6 Orange

There's no "crossover" MMJ cable -- all MMJ cables are "straight through".  I said that it was a simpler idea.

RJ-45 to DB-9 Female
This hooks a PC's serial port to a DEC terminal server.  I left out the "handshaking" lines (RTS, CTS, DSR, DTR, DCD, RI).

    RJ-45                      DB-9 Female
    1  White / blue            1  No connection
    2  Blue                    2  Green
    3  White / green           3  Blue
    4  Brown                   4  No connection
    5  White / brown           5  White / green and White / blue
    6  Green                   6  No connection
    7  White / orange          7  No connection
    8  Orange                  8  No connection
                               9  No connection

Digital made an adapter, H8585-AA, with the following pinouts.  Could this be the full-handshaking version of the above?  I haven't tested it, but it would seem likely.

    RJ-45                      DB-9 Female
    1  White / blue            1  Connect to pin 6 and White / orange
    2  Blue                    2  Green
    3  White / green           3  Blue
    4  Brown                   4  Orange
    5  White / brown           5  White / green and White / blue
    6  Green                   6  Connect to pin 1 and White / orange
    7  White / orange          7  Brown
    8  Orange                  8  White / brown
                               9  No connection

RJ-45 to DB-25 Male
This hooks a DEC terminal server to a modem.  The handshaking lines are used in this one.  Unfortunately, there's no place on a RJ-45 for DCD or RI.  Digital made an adapter for this called the H8585-AC.

    RJ-45                  DB-25 Male
    1  White / blue         2  Green
    2  Blue                 3  Blue
    3  White / green        4  White / brown
    4  Brown                5  Brown
    5  White / brown        6  Orange
    6  Green                7  White / green and White / blue
    7  White / orange      20  White / orange
    8  Orange

Digital's DECserver 900TM could be configured to bring those signals out on the RJ-45 instead of DSR and CTS.  They made an adapter, the H8585-AB, which had these pinouts:

    RJ-45                     DB-25 Male
    1  White / blue            2  Green
    2  Blue                    3  Blue
    3  White / green           7  White / green and White / blue
    4  Brown                  8  Orange
    5  White / brown          20  White / orange
    6  Green                  22  Brown
    7  White / orange         23  White / brown
    8  Orange

RJ-45 to MMJ
This is probably the hardest cable to make.  That's because both of these are crimp-on connectors.  First, the pinouts:

    RJ-45                   MMJ
    1  White / blue         1  Orange and brown
    2  Blue                 2  Blue
    3  White / green        3  White / blue
    4  Brown                4  White / green
    5  White / brown        5  Green
    6  Green                6  White / orange
    7  White / orange
    8  Orange

See how the first wire in the MMJ needs to connect to two wires on the RJ-45?  What I do is cut off about 2 inches of the outer cover on the cable near the MMJ end (before I put on the MMJ!).  I cut off the White/brown wire (it doesn't go to the MMJ), and strip all the insulation off the Brown wire.  I then carefully (very carefully) strip about 1/2 inch of insulation off the Orange wire.  If you do this right, the Orange wire's insulation just slips up.  I then wrap the two wires together.  I put the outer insulation back on, less about 1/2 inch.  A piece of electrical tape makes it secure.  I then put on the MMJ as indicated.

Digital's BN24H cable was similar to the above, but without the brown wire being hooked to pin 1 of the MMJ.

Digital did make an adapter, the H8584-AC, with the following pinouts.  This is a RJ-45 plug and MMJ socket.

    RJ-45                     MMJ Socket
    1  White / blue           1  White / orange
    2  Blue                   2  Green
    3  White / green          3  White / green
    4  Brown                  4  White / blue
    5  White / brown          5  Blue
    6  Green                  6  Orange and brown
    7  White / orange
    8  Orange

RJ-45 (DECserver) to RJ-45 (Cisco router)
To connect a Cisco router's console port to a DECserver terminal server (thanks to Jim Azbell):

    RJ-45 (DECserver)         RJ-45 (Cisco)
    1  White / blue           1  Brown
    2  Blue                   2  Orange
    3  White / green          3  Blue
    4  Brown                  4  White / blue
    5  White / brown          5  White / green
    6  Green                  6  Green
    7  White / orange         7  White / orange
    8  Orange                 8  White / brown

RJ-45 (FlowPoint) to DB-9 Female
To connect a FlowPoint router's console port to a PC's serial port (from http://support.efficient.com/docs/pdf/Techrefguide.pdf):

    RJ-45                     DB-9
    1  White / blue           1  no connection
    2  Blue                   2  White / blue
    3  White / green          3  Brown
    4  Brown                  4  no connection
    5  White / brown          5  White / brown
    6  Green                  6  no connection
    7  White / orange         7  Blue
    8  Orange                 8  Green
                              9  no connection

MMJ to DB-25 Female
This hooks an older PC's serial port to a Digital MMJ device (such as a VT220 terminal).  Digital made an adapter called a H8575-A with these pinouts:

    MMJ                       DB-25 Female
    1  Orange                  2  Blue
    2  Blue                    3  Green
    3  White / blue            4  Connect to pin 5
    4  White / green           5  Connect to pin 4
    5  Green                   6  Connect to pin 8 and White / orange
    6  White / orange          7  White / blue and White / green
                               8  White / orange and pin 6
                              20  Orange

MMJ to DB-9 Female
This hooks a PC's serial port to a Digital MMJ device (such as a VT220 terminal).  Digital made an adapter called a H8571-J with these pinouts:

    MMJ                      DB-9 Female
    1  Orange                1  Connect to pins 6 and 8 and White / orange
    2  Blue                  2  Green
    3  White / blue          3  Blue
    4  White / green         4  Orange
    5  Green                 5  White / blue and White / green
    6  White / orange        6  Connect to pins 1 and 8 and White / orange
                             7  No connection
                             8  Connect to pins 1 and 6 and White / orange
                             9  No connection
Note:  The pinouts for early MicroVAX systems do not follow this scheme.  See the VMS FAQ for details.

DB-9 Male (Intermec) to DB-9 Female
This hooks a PC's serial port to an Intermec 9154 scanner's management port.  This is Intermec cable number 060728-00028.

    DB-9 Male                  DB-9 Female
    1  No connection           1  White / blue
    2  Blue                    2  Green
    3  Green                   3  Blue
    4  No connection           4  No connection
    5  Orange                  5  White / green
    6  No connection           6  No connection
    7  White / green           7  No connection
    8  No connection           8  Orange
    9  White / blue            9  No connection

Please feel free to email Quayle Consulting!

Please note:  If you want a cable for a device not specified here, you must supply the pinouts of the device!

The AirBorn page in Australia has some good stuff:  http://www.airborn.com.au/rs232.html

The VMS FAQ has lots of good info.

This DEC cable manual is handy:  Cable-guide.html

NullModem.com has lots of pinouts

More DECconnect adapters are here:  http://www.lammertbies.nl/comm/cable/dec-mmj.html

B&B Electronics makes some good devices, and has lots of reference materials.

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