UG-1032 6LAP5 LAN Adapter Panel Dual Modem
Copyright © 2016 QEI
Connection to the Line Transformers
5
5 Connection to the Line Transformers
The modem connections to external line transformers are made via a 6-pin MOLEX
type connectors. The connector pinout is as follows:
Connector
Functions
J2-Part 2 J1-Port 1
Pin 1
4-Wire Transmit HI.
Pin 2
4-Wire Transmit RETURN.
Pin 3
Common
Pin 4
4-Wire Receive or 2-Wire Transmit/Receive HI.
Pin 5
4-Wire Receive or 2-Wire Transmit/Receive RETURN.
Pin 6
PTT (Push-to-Talk, open collector). The push-to-talk
output is capable of sinking 120 mA of current (@12Vdc)
to the circuit common when active.
6 LED Indicators
LED D5 and D10 separately indicate the functional status of the modem 1 and
modem 2 of the 6LAP5 modem micro-controllers. The LED flashes at a 2 Hz rate
during normal operation. When the modem cannot communicate with the 6CPP6
Central Processor Panel, there will be a momentary interruption (or brief blink) to the
flashing pattern, occurring every five seconds. Additional port activity (TX, RX, and
RTS) LEDs are located on the 6CPP6 Central Processor Panel.
7 Functional Description
Each 6LAP5 modem consists of two functional sections: both of these sections are
Bell 202 compatible modem interfaces. The following paragraphs give a brief
description of the operation of these sections.
7.1 Bell 202 Compatible Modem
Each modem section consists of a single-chip modem IC, and a micro-controller. The
modem IC is capable of transmitting and receiving according to the Bell 202 format
which is a standard that is used over leased or dedicated phone lines. It uses a FSK
(frequency shift keying) modulation and de-
modulation technique where logic “0”
(SPACE) is
transmitted at 1200 Hz, and logic “1” (MARK) is transmitted at 2200 Hz.
An amplification stage boosts the modem transmitter output to the required line
levels. External transmit and receive coupling transformers are needed. These
transformers are generally installed in the 6PCP6 power supply.
The gain of the amplifier is jumper selectable for -12, -9, -6, -3, and 0 dBm measured
across the external transformer with 600ohm termination. The output of the amplifier
is fed to a FET switch which gates the transmission out onto the communication line
when the transmitter is active. The switch is controlled by the micro-controller.
Another amplifier is connected to the modem receiver input. Its gain is jumper
selectable for -30 or -45 dBm input sensitivity, also measured across the external
transformer of 600 ohm line. The micro-controller initializes the modem IC and
