Models 92 & 77 - Sync/Async Short Haul Modems
Reference Manual


Table of Contents

1.0 General Description
2.0 Specifications
3.0 Installation
4.0 Operation
5.0 Troubleshooting
6.0 Power
7.0 Help
Warranty



1.0 General Description

The Models 92 and 77 Synchronous / Asynchronous Short Haul Modems are designed for synchronous or asynchronous serial data communications over 4 wire dedicated (or leased) lines that provide DC continuity. The Model 92 is a stand alone unit while the Model 77 is a card version that can be placed in Telebyte's model 76-3 or 76-4 Card Cage giving the user the ability to place up to 14 Model 77's at one location. Both units operate at 5 different Baud rates from 1200 to 19,200 and are completely independent of line protocols and data formats.

2.0 Specifications

Interface: EIA RS-232/CCITT V.24, V.28

Connectors:
Model 92 - Male DB-25
Model 77 - 76-3 or 76-4 card cage Female DB-25

Line Connection:
Model 92 - RJ-11 and screw terminals
Model 77 - 76-3 - 4 wire strip connections 76-4 - RJ-11

Transmission Mode: Serial Synchronous or Asynchronous

Transmission Format: Manchester Encoding (Sync only)

Transmission Medium: 4 wire unconditioned line, two twisted pairs.

Data Rate:
Sync - 1200 to 19,200 five rates, jumper selectable
Async - 0 to 19,200 transparent

Range: Dependent on wire gauge and type, clock selection and user environment.

Baud Rate Distance (Miles)
26 AWG
1200 5.0
2400 4.0
4800 3.0
9600 2.0
19,200 1.0


Front Panel Indicators: Model 77 only- TD, RD, RTS, CTS, DCD, DTR and Power.

Operator Controls: Model 92 and 77-Sync/Async Option, Baud Rate Selection, Clock Source, DCD Constant/Switched.
Model 77 only- Power Switch, Loopback Switch.

Control Signals:
CTS turns "ON" immediately after terminal raises RTS.
DCD can be strapped "ON" or controlled by transmit carrier.

Power:
Model 92 - None required. Uses low power from EIA data and control signals.
Model 77 - 110 VAC 50/60 Hz supplied to 76-3 or 76-4

Size:
Model 92 - 3.5"L x 2"W x .875"H
Model 77 - 1"W x 4.5"H x 7"D

Environment: 0° to 50° C, 5 to 95% RH (no condensation)

3.0 Installation

3.1 Digital Interface
The digital interface for both units is configured as DCE. The following signals are supported:

Pin# CCITT EIA Source Name
1 (92) 101 AA --- Chassis GND
2 103 BA DTE Transmit Data
3 104 BB DCE Receive Data
4 105 CA DTE Request to Send
5 106 CB DCE Clear to Send
6 107 CC DCE Data Set Ready
7 102 AB --- Signal GND
8 109 CF DCE Data Carrier Detect
15 114 DB DCE Transmit Clock
17 115 DD DCE Receive Clock
20 108.2 CD DTE Data Terminal Ready
24 113 DA DTE Ext Transmit Clock

NOTE:
DTE represents an input to the modems
DCE represents an output from the modem


For the units to begin transmitting RTS and DTR must both be asserted.

3.2 Analog Interface

The analog interface for the Model 92 consists of an RJ-11 and a 4 screw terminal block. For the Model 77 it is a 4 wire strip connector located on the rear panel of the 76-3 card cage or an RJ-11 on the Model 76-4 card cage. When connecting a Model 92 or a Model 77 to each other or another unit T+ goes to R+, T- to R-, R+ to T+ and R- to T-. Pin out for the Model 92 RJ-11, 76-3 strip connector and 76-4 RJ-11 are shown below in Figure 1.

Connections must be made using metallic twisted pairs with end-to-end DC continuity. Cables should be high quality 26 gauge (or larger) stranded wire. Solid conductors should not be used for long transmission lines at rates above 1200 Baud. When connecting two units special care must be made to insure that the transmit T+ & T-, are members of the same twisted pair and that the R+ & R- is the other pair.

Figure 1

4.0 Operation

4.1 Selecting A Clock Source

Model 92 and Model 77 can operate at one of five internally or externally generated Baud rates at rates up to 19.2K Baud. The units provide transmit and receive clock on Pins 15 and 17 respectively and accepts a clock signal on Pin 24. Jumpers are provided in order to enable various sources of systems clocks.

The chart below describes a configuration of two modems, a computer (CPU), and a terminal. The clocking options refer to the sources of the system clock. There are three possible sources of the clock. A system clock could be generated internally by either modem, or provided externally by the CPU or terminal or finally two clocks would be provided externally by the CPU and the terminal. In the two clock configuration where the frequency of the data going in one direction is slightly different (within +/- 20%) than the data in the other direction. The last option is recommended only if the devices at both ends of link must provide an external clock to the modems. See Figure 2 for jumper positions.

To configure the units according to your system choose on of the following options:

Figure 2: Model 92 Jumpers

Clock
Source
Modem Connected
to Source
Other
Modem
External 92 = SW1-A
        SW5-1(ON)
SW1-A
SW5-3(ON)
77 = Jumper L,P Jumper J,P
Modem 92 = SW1-A
        SW5-2(ON)
SW1-A
SW5-3(ON)
77 = Jumper K,P Jumper J,P
Both
External
92 = SW1-A
        SW5-1(ON)
SW1-A
SW5-1(ON)
77 = Jumper L,P Jumper L,P

Note: Model 92-Only one either 1, 2, or 3 maybe on for SW5. The other two must be OFF.

The normal configuration for both the Model 92 and 77 is for external clock sources from CPU or Terminal.

Factory Settings are for the 92 SW1-A, SW5-1 ON and for the 77, jumpers on L&P.

4.2 Baud Rate Selection

The model 92 and model 77 can operate synchronously at 1200, 2400, 4800, 9600 or 19.2K Baud. To configure your unit follow the table below.

Baud Rate Model 92
SW 5
Model 77
Jumper
  4 5 6 7 8 C D E F G
1200 ON OFF OFF OFF OFF X        
2400 OFF ON OFF OFF OFF   X      
4800 OFF OFF ON OFF OFF     X    
9600 OFF OFF OFF ON OFF       X  
19,200 OFF OFF OFF OFF ON         X

X = Jumper Installed

Only one switch (or jumper) should be in the ON positions.

4.3 Description of Front Panel Indicators (Model 77 Only)

The front panel indicators allow the operators to verify quickly that the unit and communications link are operating correctly. The following conditions are required to illuminate each of these indicators.

TD - Pin 2 of the EIA interface displays a Space level. This indicator should flicker ON and OFF during actual data transmission.

RD - The received data from the modem, Pin 3 of the EIA interface, displays a Space level. This indicator should flicker ON and OFF during actual data transmission.

RTS - The terminal is holding Pin 4 high.

CTS - RTS has been asserted and is holding Pin 5 high.

DCD - The modem is receiving a valid carrier from the remote unit or has been strapped to be constantly ON.

DTR - The terminal is holding Pin 20 high.

Power - The unit is receiving power from the card cage.

4.4 Data Carrier Detect

Data carrier Detect, DCD, has the option of being strapped constantly on or controlled by the transmit carrier.

Constant Controlled
Model 92 SW2-A SW2-B
Model 77 Jumper A Jumper B

4.5 Loopback Switch (Model 77 only)

The loopback switch is provided to simplify troubleshooting. Setting the switch to loopback mode (switch in) loops both the internal and external analog interfaces back onto themselves. It is equivalent to connecting T+ to R+ and T- to R- on the unit. It allows for the local testing of the local modem and in addition it connects the signal from the remote modem onto itself thus providing a test of the remote unit and the 4 wire line.

4.6 Asynchronous Operation

The Model 92 and 77 have the ability to be used in areas where asynchronous data is to be transmitted. To enable the asynchronous mode configure the units as follows:

Model 92 - SW3-A and SW4-A
Model 77 - Jumpers I and M

5.0 Troubleshooting

If either unit is not working properly it is recommended that troubleshooting be done in the loopback mode. To configure the 92 for loopback connect T+ to R+ and T- to R- and for the Model 77 push the loopback switch in. For loopback use RS-232 device in a full duplex synchronous mode. The Model 92 or 77 loops back data received on TD to RD, and that data should be displayed on the RS-232 device. If the loopback test does not work check for the following:

Condition Verify
1. Model 77 power indicator. Check that the card cage is plugged in and that the master power supply is on.
2. RTS and DTR are both off. Check that the RS-232 device raises RTS and DTR when it wants to transmit.
3. TD is working but no RD or DCD. Check 4 wire line for proper connection.
4. Wrong data is being received. Check that the Baud rate is set the same for both units. Both units are configured for either sync or async.

6.0 Power

For the model 92 power is derived from the RS-232 interface and for the Model 77 power is supplied by the card cage.

7.0 Help

Assistance can be obtained by visiting our Technical Support Center.

Warranty

Telebyte warrants the equipment to be free from defects in material and workmanship, under normal and proper use and in its unmodified condition, for 12 months, starting on the date it is delivered for use. TELEBYTE's sole obligation under this warranty shall be to furnish parts and labor for the repair or replacement of products found by TELEBYTE to be defective in material or workmanship during the warranty period. Warranty repairs will be performed at the point of manufacture. Equipment approved for return for warranty service shall be returned F.O.B. TELEBYTE factory and will be redelivered by TELEBYTE freight prepaid, except for non- continental U.S.A. locations. These deliveries will be sent COD freight and import/export charges.

THE ABOVE WARRANTY IS IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED OR IMPLIED, STATUTORY OR OTHERWISE, INCLUDING ANY IMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. TELEBYTE SHALL NOT BE LIABLE FOR ANY DAMAGES SUSTAINED BY RESELLER OR ANY OTHER PARTY ARISING FROM OR RELATING TO ANY EQUIPMENT FAILURE, INCLUDING, BUT NOT LIMITED TO CONSEQUENTIAL DAMAGES NOR SHALL TELEBYTE HAVE ANY LIABILITY FOR DELAYS IN REPLACEMENT OR REPAIR OF EQUIPMENT.

Out of warranty equipment may be returned to the Greenlawn, NY customer service facility prepaid as described above. Return shipping charges will be billed to the customer. The repaired unit will have a 90 day warranty. In those cases where "NO TROUBLE" is found, a reduced charge will be billed to cover handling, testing and packaging.

Whether in or out of warranty a Return Material Authorization number (RMA) is necessary
. Assistance can be obtained by visiting our Technical Support Center.

Document No. 0315-0101/Rev. A

Model Product Info
92  Product Page  Application Note  Specifications
77 The Model 77 is obsolete.

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