CTI Products NCB/EM with External PSTN Modem User Manual
Page 57
CTI Products, Inc.
NCB-EM User Guide
Appendix G. Modem Notes
51
4-wire Leased-Line Wire-color/Connection Method
For actual connection to the telephone circuits in the field, the following table shows typical telephone circuit
connector schemes and functions:
Telco Connector
Color / Pins
Function
Connect to NCB LINE Pins:
42A Block
Red & Green
Yellow & Black
Transmit
Receive
3 & 4 (Red & Green)
2 & 5 (Yellow & Black)
66 Block
(Punch Block)
Top-most pair
Bottom-most pair
Transmit
Receive
3 & 4 (Red & Green)
2 & 5 (Yellow & Black)
RJ45 (8 Pin)
Pins 1 & 2
Pins 7 & 8
Transmit
Receive
3 & 4 (Red & Green)
2 & 5 (Yellow & Black)
The above data is typical in most situations, but sometimes wire pairs get flipped, causing this information to be
incorrect. If the modem units do not properly communicate after connecting the pairs as above, use the
following procedure to determine proper wire pairs:
1. Disconnect all four wires between both modems and their associated telephone circuit wiring.
2. At the site containing the modem in originate mode, connect pins 3 & 4 (Red & Green) from this
modem to either telephone circuit pair (use the pair you suspect is the transmit pair that carries audio
from the originate-mode modem to the answer-mode modem, if you believe you know which one this
is).
3. Be sure this originate-mode modem has switches set correctly, and that this modem was reset or
power-cycled after any switches were changed.
4. At the site containing the modem in answer mode, connect pins 2 & 5 (Yellow & Black) from this
modem to either telephone circuit pair.
5. Increase the volume on the rear panel of the modem.
6. Be sure this answer-mode modem has switches set correctly, and that this modem was reset or power-
cycled after any switches were changed.
7. Listen for a periodic single tone with about a four second repitition rate. This is a tone from the
originate-modem to the answer-modem.
8. If you hear this tone you have correctly chosen the transmit telephone pair. Proceed by connnecting
the remaining pair from each modem to each remaining telephone circuit pair at each site. Reset both
modems (or wait for them to timeout and recycle, approximately 60 seconds) and they should complete
the modem training process and turn on their “CD” LEDs within 30 seconds.
9. If you do not hear this periodic tone from the answer-mode modem, try changing the connection of
pins 2 & 5 (Yellow & Black) of this answer-mode modem to the other telephone circuit pair at this
site. Reset both modems and again listen for the periodic tone from the answer-mode modem.
10. If step 9 still does not result in a periodic tone, go back to the site of the originate-mode modem and
change the connection of pins 3 & 4 (Red & Green) of this originate-mode modem to the other
telephone circuit pair at this site. Reset both modems and return to the site of the answer-mode
modem and listen for the periodic tone.
11. If the actions of step 9 and/or 10 still do not result in a periodic tone, either the telephone circuit or the
modem(s) must be defective. Have the telephone company installer check the telephone circuit for
proper operation and labeling of the transmit and receive channels at both sites.
12. If the actions of step 9 or 10 do result in a periodic tone, proceed by connnecting the remaining pair
from each modem to each remaining telephone circuit pair at each site. Reset both modems (or wait
for them to timeout and recycle, approximately 60 seconds) and they should complete the modem
training process and turn on their “CD” LEDs within 30 seconds.
See text in section “2.
”,
” for important information
when connecting two modems “back-to-back” in Leased-Line mode with a short phone cable.
Certain leased-line audio circuits (most notably microwave RF channels) provide a 4-wire circuit made up of a
Transmit pair and a Receive pair. Use the 4-Wire mode in these situations. Be sure to provide proper wiring in
4-Wire mode.