Data communication Cables

Crimp to sub D
Null modem cable LapLink cable
UTP Cross cable
V36 / RS449 to V35 cable

Crimp to sub D

In PCs, a sub-D connector (LPT or COM) is often connected to a crimp or IDC (Insulation displacement connector) by means of a ribbon cable. IDCs have two rows of pins. One is even, the other odd numbered;

 1  o o  2
 3  o o  4
 5  o o  6
 7  o o  8
 9  o o 10

Pin 1 is marked with a triangle. The corresponding wire is red.

There are two ways of connecting these to a DB9 or DB25 connector;

  1. Match the pin numbers.
  2. Connect a row on the IDC to a row on the sub-D.

Match the pin numbers


DB9	IDC-10

1	1
2	2
3	3
4	4
5	5

6	6
7	7
8	8
9	9

Pin 10 on the IDC is not used

EG, a COM connector;

DB9 Male

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

1     DCD       6     DSR
2     RXD       7     RTS
3     TXD       8     CTS
4     DTR       9     RI
5     GND

IDC

DCD     1  o o  2       RXD
TXD     3  o o  4       DTR
GND     5  o o  6       DSR
RTS     7  o o  8       CTS
RI      9  o o 10       Not Connected

This system is well suited for soldering the sub-D connector.

Match the rows


DB25    IDC26

 1      1
 2      3
 3      5
 4      7
 5      9
 6     11
 7     13
 8     15
 9     17
10     19
11     21
12     23
13     25

14      2
15      4
16      6
17      8
18     10
19     12
20     14
21     16
22     18
23     20
24     22
25     24

Pin 26 on the IDC is not used.

EG, a LPT connector;

DB25 Female

            1
      3 2 1 0 9 8 7 6 5 4 3 2 1
  ---------------------------------
   \  o o o o o o o o o o o o o  /
     \ o o o o o o o o o o o o /
       -----------------------
                 2
       5 4 3 2 1 0 9 8 7 6 5 4

 1    -STROBE   14    -AUTOFEED
 2    D0        15    -ERROR
 3    D1        16    -INIT PRINTER
 4    D2        17    -SELECT INPUT
 5    D3        18    GND
 6    D4        19    GND
 7    D5        20    GND
 8    D6        21    GND
 9    D7        22    GND
10    -ACK      23    GND
11    BUSY      24    GND
12    P. END    25    GND
13    SELECT

IDC

-STB    1  o o  2    -AFD
D0      3  o o  4    -ERROR
D1      5  o o  6    -PINIT
D2      7  o o  8    -SLIN
D3      9  o o 10    GND
D4     11  o o 12    GND
D5     13  o o 14    GND
D6     15  o o 16    GND
D7     17  o o 18    GND
-ACK   19  o o 20    GND
BUSY   21  o o 22    GND
PE     23  o o 24    GND
SLCT   25  o o 26    Not Connected

This system is well suited for crimp sub-D connectors.

Null Modem cable


RXD--------\   /--------RXD
             X 
TXD--------/   \--------TXD

RTS--------\   /--------RTS
             X
CTS--------/   \--------CTS

DTR--------\   /--------DTR
             X
DSR--*-----/   \-----*--DSR
     |               |
DCD--+               +--DCD

GND---------------------GND

The screen of the cable should be connected (soldered) to the connector shell at both ends of the cable.

Null Modem cable with 9 pins connector


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

        DB9 Female

 2 --------\   /--------  2
             X 
 3 --------/   \--------  3

 7 --------\   /--------  7
             X
 8 --------/   \--------  8

 4 --------\   /--------  4
             X
 6 --*-----/   \-----*--  6
     |               |
 1 --+               +--  1

 5 ---------------------  5

Null Modem cable with 25 pins connector

              1
        3 2 1 0 9 8 7 6 5 4 3 2 1
    ---------------------------------
     \  o o o o o o o o o o o o o  /
       \ o o o o o o o o o o o o /
         -----------------------
                   2
         5 4 3 2 1 0 9 8 7 6 5 4

               DB25 Female

 3 --------\   /--------  3
             X 
 2 --------/   \--------  2

 4 --------\   /--------  4
             X
 5 --------/   \--------  5

20 --------\   /-------- 20
             X
 6 --*-----/   \-----*--  6
     |               |
 8 --+               +--  8

 7 ---------------------  7

Null Modem cable 25 pins to 9 pins


25 pins                 9 pins

 3 --------\   /--------  2
             X
 2 --------/   \--------  3

 4 --------\   /--------  7
             X
 5 --------/   \--------  8

20 --------\   /--------  4
             X
 6 --*-----/   \-----*--  6
     |               |
 8 --+               +--  1

 7 ---------------------  5

LapLink cable

This cable can also be used for interlink and plip

D0----------------------ERROR
D1----------------------SELECT
D2----------------------PE
D3----------------------ACK
D4----------------------BUSY

ACK---------------------D3
BUSY--------------------D4
PE----------------------D2
SELECT------------------D1

ERROR-------------------D0

GND---------------------GND

                          1
        1 2 3 4 5 6 7 8 9 0 1 2 3
    ---------------------------------
     \  * * * * * * * * * * * * *  /
       \ * * * * * * * * * * * * /
         -----------------------
                     2
         4 5 6 7 8 9 0 1 2 3 4 5

                DB25 Male

 2 --------------------- 15
 3 --------------------- 13
 4 --------------------- 12
 5 --------------------- 10
 6 --------------------- 11

10 ---------------------  5
11 ---------------------  6
12 ---------------------  4
13 ---------------------  3

15 ---------------------  2

18 ... 25 -------------- 18 ... 25

UTP Cross cable


+ TXD ----\       /---- + TXD
            \   /
- TXD ----\   X   /---- - TXD
            X   X
+ RXD ----/   X   \---- + RXD
            /   \
- RXD ----/       \---- - RXD


    1 ----\       /---- 1
            \   /
    2 ----\   X   /---- 2
            X   X
    3 ----/   X   \---- 3
            /   \
    6 ----/       \---- 6

V36 - RS449 to V35 cable

I wonder to which extend these standards are in fact compatible.

  1  Scr   A
  2
  3
  4  ---   P
  5  ---   Y
  6  ---   R
  7  ---   C
  8  ---   V
  9  ---   D
 10  ---   L
 11  ---   E
 12  ---   H
 13  ---   F
 14  ---   N
 15
 16
 17  ---   U
 18  ---  NN
 19  GND   B

 20  GND
 21
 22  ---   S
 23  ---  AA
 24  ---   T
 25
 26  ---   X
 27
 28
 29
 30
 31
 32
 33
 34
 35  ---   W
 36
 37  GND

The pins marked `GND' are connected to each other.
The pin marked `Scr' is connected to the shield.