GDI 4xxSA User Manual

Model 4xxSA

Stand Alone

FSK Modem

USER GUIDE

(TI) 4 Jan 06

GDI COMMUNICATIONS LLC

PO Box 1330

280 I-80 Exit 1

Verdi, NV 89439

Phone: [phone]

Fax: [phone]

Email: [e-mail]

Contents

Modem Basics 3

Communication Sequence of Events……………………………………………...4

The Pole…………………………………………………………………………...4

The Response……………………………………………………………………...5

Introduction to the 4xxSA Series of Modems 6

Model 4xxSA Modems…...……………………………………………………….6

The KOD Option………...…………………...……………………………………6

Front, Rear and Bottom Panels…………………………………….…………..7

Front Panel………...………………..……………………………………………7

Front Panel LED’s……………………………………………………………....7

Rear Panel……………………..…………………………………………..……..8

Dual Data Ports…………………………………………………………………8

Copper FSK…………………………………………………………………….8

Power Connections……………………………………………………………..8

Bottom Panel……………………………….……………...…………...………...9

DIP Switches……………………………………………………………………9

Full or Half Duplex………………………….……………………………….9

RTS to CTS Time…………………………………………………………….9

Carrier Turn Off Time………………………………………………………..9

Local Echo……………………………………………………………………9

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Contents……continued

Receiver Squelch Time………………………………………………………9

Carrier Detect………………………………………………………………...9

Load Compensation…………………………………………………………10

KOD Function………………………………………………………………10

KOD Direction……………………………………………………………...10

KOD Delay………………………………………………………………….10

Anti-Streaming……………………………………………………………...10

Data Protocol………………..…………………………………………...……...10

RS232………………………………………………………………………….10

RS422………………………………………………………………………….10

Applications _________ ___11

Half Duplex Operation (2 Wire)……………….………………………………...11

Full Duplex Operation (4 Wire).………………………………………………...12

Modems with the KOD Option Installed………………………………………..13

Internal KOD…………………………………..……………………………13

External KOD……………………………………………………………….13

KOD Applications…………………………………………………………..14

More Applications………………………………………………..................15

Repeater Applications……………………………………………………………16

A Word on Dynamic Range……………………………………………………..17

Notes……………………………………………………………………………..18

4xx Preliminary Generic User Guide. 4 Jan 06 2

Modem Basics

The term Modem is a combination of two words, Modulator and Demodulator.

Modem

Frequency Shift Keying (FSK) Modems are designed to convert digital data to
tone frequencies, this process is called modulation. The frequencies can easily be
transmitted via a communication line to the receiving modem. At the opposite end
of the communication line the tone frequencies are converted back to digital data
by a process known as demodulation. By using this mechanism, two digital
devices, such as Traffic Maintenance Center’s (TMC) Computer and a Remote
Controller can communicate with each other via the outside cable plant.

The 4xx series of modems use a modulation technique known as Frequency Shift
Keying (FSK). Digital information is binary in format: that is, data is represented
by either logic high or logic low (1 or 0). Communications terminology refers to
logic Low as Mark and logic High as a Space. FSK Modems utilize this fact and
generate a unique frequency for each logic level. Each model in the 4xx series
have their own unique set of frequencies due to the baud rate therefore only
modems of the same model number can communicate with each other, see the
following chart.

Baud Rate
Mark Frequency
Space Frequency
Soft Carrier

The rate at which the communication line changes state is known as the baud rate,
this can be interpreted to be equivalent of bits per second.
The 4xx Series of Modems are capable of communicating at baud rates up to
19200Kbts depending on the model.

Digital

Transmit Section of

Modem 1

Modulator DemodulatorTransmit Cable Pair

Input/Output

1200 9600 19200

Low (0) 1200Hz 11200Hz 19200Hz

High (1) 2200Hz 17600Hz 38400Hz

900Hz 7800Hz 13800Hz

Tones

Receive Section of

Modem 2

Digital

Model # RS232

400SA 496SA 419SA

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Communications Sequence of Events

For ease of understanding this sequence of events we will limit our discussions to
one modem at the TMC and one Remote modem connected to a Controller over a
4 wire system.
Note; Transmit and receive pairs are referenced to the “Master” end of a 4 wire
circuit, also a modem has a Transmit Section and a Receive Section.

The Pole

TMC

Computer

“Master”

RTS
CTS

DATA

Transmit

Section

Transmit Pair

Receive
Section

CD

DATA

Remote

Controller

1. The TMC computer (Master) signals the modem that it wants to transmit
data by raising Request To Send (RTS) at the modems input. The modem
returns a Clear To Send (CTS) back to the TMC computer after a time
delay (user selectable). This is called Handshaking.
As soon as the “master” modem sees RTS it transmits a Mark tone down
the copper wire to wake up the remote modem.

2. The Remote Modems Carrier Detect (CD) circuit sees the Mark tone. If
the tone is continuous for 4 or 8ms (user selectable) the Carrier Detect
circuit will validate it and unlock the receivers output (removes Receiver
Squelch) and raise CD at the data port. This CD signal advises the
Controller to expect data. The demodulated Mark tone, logic 0, is passed
to the RS232 Data port, where it does not change state due to the fact that
when not in use it is always at logic 0, same as the transmit end. Now let’s
go back to the TMC end.

3. Once the TMC computer receives CTS (clear to send) it will send data to
the modem. At this juncture both modems on the system are in a “go”
state.

4. The TMC computer now sends data (0’s and 1’s) to the modem which
converts it to Mark and Space frequencies. These frequencies (tones) are
then transmitted down one pair of wires known as the transmit pair to the
Remote modems receiver.
When the data ends, RTS is lowered and the modem transmits a short
burst of Soft Carrier (tone is out of band of the Mark/Space frequencies).
This lower frequency tone causes the receiving modem to squelch the
input to the digital circuits. This action “closes the modems door” to
prevent noisy lines from false triggering the data circuits. The modem is
now quiet.

5. We have now completed the Polling phase.

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The Response

TMC

Computer

CD

DATA

Receive

Section

Receive Pair

Transmit

Section

RTS
CTS

DATA

Remote

Controller

1. The Controller recognizes its address and prepares a message to be sent
back to the TMC computer. Our response message will be sent back to the
TMC on the Receive Pair of the 4wire system.

2. The Controller (Remote) signals the modem that it wants to send data by
raising Request To Send (RTS) at the modems input. The modem returns a
Clear To Send (CTS) back to the Controller after a time delay (user
selectable). This is called Handshaking.
As soon as the “remote” modem sees RTS it transmits a Mark Tone down
the copper wire to wake up the “Master” modem.

3. The TMC Modem’s Carrier Detect (CD) circuit sees the Mark tone. If the
tone is continuous for 4 or 8ms (user selectable) the Carrier Detect circuit
will validate it and unlock the receivers output (removes receiver squelch)
and raise CD at the data port. This CD signal advises the TMC computer
to expect data. The demodulated Mark tone, logic 0, is passed to the
RS232 Data port, where it does not change state due to the fact that when
not in use it is always at logic 0, same as the Controller end. Now let’s go
back to the Controller end.

4. Once the Controller receives CTS (clear to send) it will send data to the
modem. At this juncture both modems on the system are in a “go” state.

5. The Controller now sends data (0’s and 1’s) to the modem which converts
it to Mark and Space frequencies. These frequencies (tones) are then
transmitted down the receive pair of wires to the TMC modems receiver.

6. At the TMC modems receiver the Mark and Space frequencies are
demodulated into 0’s and 1’s respectively. This is the same bit pattern that
the Controller sent to the modem for transmission. This data is then sent to
the TMC computer via the communication port.
When the data ends, RTS is lowered and the modem transmits a short
burst of Soft Carrier (tone is out of band of the Mark/Space frequencies).
This lower frequency tone causes the receiving modem to squelch the
input to the digital circuits. This action “closes the modems door” to
prevent noisy lines from false triggering the data circuits. The modem is
now quiet.

7. We have now completed the Response phase.

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