NEC 9A
______                           __                             __
                                 ||                             ||
 25 Pin D-Plug(LPT1)             ||                             ||
____________________             ||                             ||
                                 ||                             ||
Pin                             _||__________         __________||__
  1.green                       |           |         |            |
  6.-|<1n4148------             | phone     /          \  phone    |
  8.-|<1n4148--   |             |          /            \          |
              |   |             |          |            |          |
              |   |      back-->|          |<---front-->|          |<--back
 10.-----------   |             |          |            |          |
 13.-----------------red        |          \            /          |
 15.------blue                    | | | |                 | | | |
 18.------black                       |                     / |  \
                                      |                    /  |   \
                                    black             blue/ green  \red

Diodes = 1N4148

NOTE Diode protocol: Kathode---|<diode---Anode