Model 290



Reference Manual

0315-0139 Rev. B


Printed 08.15.05

Table of Contents

1.0 Introduction

2.0 Specification
2.1     Spec Notes

3.0 General Description

4.0 Indicators
4.1     Master Port
4.2     Slave Ports

5.0 Port Selection Switches

6.0 Connector Information
6.1     Master Port
6.2     Slave Ports

7.0 Surge Protection
8.0 Help

1.0 Introduction

This manual describes the operation of the Model 290 RS-422/RS-485 Concentrator. It performs the function of merging up to 16 RS-422 or RS-485 ports into a single RS-232 master port. The slave ports can be independently programmed to accommodate either four-wire RS-422 or two-wire RS-485.


2.0 Specification

Interface: Master port: RS-232

Slave ports: RS-422 or RS-485

Date Rate: DC to 64 KBPS

Indicators: 37 LED's, TD and RD for each port and power

Switches: 16 individual port selection switches for RS-422 or RS-485
Connectors: Master port: DB25 female

Slave ports: Four-wire, six-position RJ-11

Power: Five-pin Din

Earth Ground: #6-32 post

Surge Protection: Avalanche diodes, 500 watts, response time less than five nanoseconds



Average Clamp Voltage

Maximum Clamp Voltage

Peak Current (Amps)










Power: 110 Volts, 60 Hz (220 Volts, 50 Hz optional)

Housing: Steel, painted

Size: 16" W x 8" D x 1.7" H

Environment: Operating temp 0o to 50o C Humidity _ 5 to 95% RH, no condensation

MTBF: 135,000 hours


2.1 Spec Notes

2.1.1 Line Termination

The Model 290 is designed to provide data transmission up to 64 KBPS. When using RS-485 data transmission it is recommended that the far-end transceiver be terminated in 120 Ohms. When this is done the Model 290 will support link distances up to 4,000 feet at data rates to 64 KBPS. If the link is not terminated the link distance is decreased to 1,000 feet. This reduction is due to reflections on the cable that might otherwise appear as erroneous data on the output of "Receive Data" on the RS-232 port. At 1,000 feet these reflections are suppressed and are not a problem.

2.1.2 Line Turn-Around Time

In any RS-485 system there exists the problem of Line Turn-Around. This is the time from the termination of the trailing edge of the last bit transmitted from the host to the time of the leading edge of the first bit transmitted by the slave. The challenge is to mask the capacitive effects of the line immediately after the last bit transmitted. The masking time in the Model 290 is 16 to 20 msec, therefore it is recommended that a duration of at least 25 msec be allowed from the trailing edge of the last received bit to the leading edge of the first bit transmitted.


3.0 General Description

The Model 290 Concentrator offers a unique group of features for applications using RS-422 and/or RS-485 for communications between a multiplicity of devices. These environments are based upon a master-slave relationship. The master port of the Model 290 is configured for RS-232 and uses "Transmit Data," "Receive Data," and "Ground." Industrial control applications are a primary example of a use for this form of communication protocol.

The Model 290 incorporates a built-in interface converter to condition the signals between the master port and any of the slave ports which are operator programmable to RS-422 or RS-485 simply by setting a dip switch on the rear panel adjacent to the RJ-11 input/output connectors. Internal intelligence allows the Model 290 to support half-duplex operation on the RS-485 single twisted-wire pair without the requirement of RTS on the master port. Full-duplex operation is supported on the RS-422 ports over two twisted-wire pairs. The port capacity of the Model 290 is 16, however, it may be expanded, in groups of 16, by using a Telebyte Model 31 Port Miser. Thus, up to 48 slave ports can be controlled by the master port via the master port of the Model 31.

Power for the Model 290 is supplied from a wall-mounted transformer with an eight-foot connectorized line cord. Because every port is surge protected, the Model 290 is equipped with a grounding stud to allow a connection to earth ground for diversion of the otherwise deadly effects of induced surges. The 16 ports are available on four-wire, six-position, RJ-11 connectors. Wiring is consistent with TELCO standards wherein the inner two contacts represent the transmit pair for the RS-422, if the port is programmed for RS-422. The outer pair of contacts in the RJ-11 modular connector represents the receive pair for RS-422 and the I/O for RS-485.


4.0 Indicators

4.1 Master Port

LED indicators for the master port provide a visual indication of full-duplex data traffic on the RS-232 port. The LED's are configured with green and red to show the active levels of the RS-232 signals in and out of the Model 290. The green represents a negative voltage while the red represents a positive voltage. In the quiescent state, with no data being transferred, only the green LED's are illuminated.

4.2 Slave Ports

Each slave port has separate "TD" and "RD" LED's. Because the master port controls the data being transmitted on the slave ports, all of the slave "TD" indicators illuminate simultaneously. The "Receive" LED for each slave port is a function of the data being presented by the external device. A positive voltage being received represents a logic "1" or LED "ON." This condition is true for both the RS-422 and RS-485 configuration.


5.0 Port Selection Switches

There are 16 dip switches on the rear of the Model 290 labeled with the port number that each switch controls. The upper position of the switch sets the selected port to RS-485 while the lower position sets it for RS-422.


6.0 Connector Information

6.1 Master Port

The wiring for the RS-232 master port is shown below:

Pin #

Function Into/Out of Model 290






Out of


Signal Ground




6.2 Slave Ports

The following diagram shows the connections for the RJ-11 slave port when set to:




7.0 Surge Protection

The Model 290 incorporates surge protection both on the RS-232 master port and the slave ports. 
The RS-232 surge protection limits surges to approximately 22 volts. 
The slave ports have surge protection that limits surges to approximately 8.2 volts.


8.0 Help

If you require assistance, please visit our Technical Support Center.


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 plus 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 (RMA) number is necessary and can be obtained by visiting our Technical Support Center. Reference the RMA number on the outside container.

Document No. 0315-0139/Rev. B

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