1.0 General Description

The Model 225 is a short haul modem designed for full duplex asynchronous communications over two sets of twisted pair wires. The Model 225 incorporates a carrier scheme so that other Model 225's may be multi-dropped from the same sets of wires. Power is provided to the Model 225 through the RS-232 interface. For full operation with regard to power, the modem requires only that Transmit Data and Ground be connected. The standard Model 225 contains an LCD display, whereas, the Model 225MX/225FX does not include the LCD display.

1.1 DataSpyŽ Feature
Your new Telebyte product incorporates the Patent Pending DataSpy feature, a LCD display designed to provide meaningful information to you, the user. It will assist during the initial installation and check out and thereafter can be used as a performance monitor. In case of a system problem, it provides information as to the status of the local link.
The Telebyte logo displayed on the LCD display indicates that the unit is powered (see Figure on following page). For power stealing devices such as your modem, it is an indication that sufficient power is being applied to operate the device. The LCD display uses less than 1 milliwatt of power.
The data display on the LCD consists of graphical representations for TD (Transmit Data) and RD (Receive Data.). Each of these signals is displayed as a bit change waveform would appear on an oscilloscope. Ordinarily, TD and RD are low or a minus voltage in the quiescent state. When data is transmitted, the transmit signal is brought high to a positive voltage. These two (2) signal states are displayed on the LCD by either a low segment or a high segment. The low segment represents the negative voltage, the mark condition, while the upper segment represents a positive voltage, the space condition. The vertical bar connecting the lower segment to the upper segment is always on when power is applied. If the transmit signal is in the quiescent state, continuously low, only the lower segments and the vertical bar will be illuminated. This is an indication of a constant negative state. If the transmit or receive inputs to the device were streaming, i.e. in the positive mode continuously, the LCD display would show the vertical segment and the upper segments only. For those cases where there is valid data transmission both the upper and lower segments will be displayed simultaneously. A variation in display intensity between lower and upper segments will give the user a perception of the amount of data being transmitted.
The LCD display also presents to the user the status of the following control signals: CTS, RTS, DSR, DCD, and DTR. These signals are displayed as mnemonic symbols composed of three letters each on the bottom line of the display. The presence of the three-letter mnemonic indicates that the respective control signal is high or positive. If the control signal is negative, the three-letter mnemonic is not displayed. For most full duplex data only modems, CTS and RTS are connected together while DSR, DCD, and DTR are connected together. For hand shaking modems there will be a relationship between various control signals on both ends of the link. This relationship is dependent upon which control signals are utilized. The DataSpy LCD display will help verify correct operation.

2.0 Specifications

2.1 Interface: Conforms to RS-232 and CCITT V.24 specifications.

2.2 Connectors
2.2.1 RS-232 : DB25M or DB25F
2.2.2 Analog : RJ-11 and 5 screw terminals

2.3 Data Rate: 0 to 19.2Kbps

2.4 Transmission: Asynchronous full duplex over 4 wires (two twisted pairs)

2.5 Transmission Controls: Data Carrier Detect, DCD, turns on after detecting the receive signal from the line. Data Set Ready, DSR, or Data Terminal Ready, DTR, will be a constant high depending on setting of DTE/DCE switch. For DTE setting Clear-To-Send, CTS, turns on 40 msec after terminal raises Request-To-Send, RTS.

2.6 Switches: Each modem is equipped with a DTE/DCE slide switch to allow reversing the TD and RD signals on the RS-232 interface as well as the proper setup of the control signals and an RTS-Cont slide switch for multi-dropped environments.

2.7 Indicators: LCD display for data, 5 control signals and power.

2.8 Transmission Range: For 24 AWG wire, 2.8 miles at 1200-9600 BPS; 1.2 miles at 19,200 BPS.

2.9 Carrier Control: The carrier is selectable as continuous or switched. In the switched mode, the carrier is controlled by RTS.

2.10 Power: Derived Power From Interface. The short haul modem/line driver will attempt to derive its power from any one of the control signals, which are expected to be at least +5.5V or -5.5Vin the quiescent state. If there are no control signals available to the modem then power is derived from the data input pin. The data input pin must be at least -5.5V in the quiescent state.

2.11 Size: 2" W x 4.15" L x .79" H (50.8mm x 105.4mm x 20.1mm)

2.12 Environment: 0° to 50° C, 5% to 95% relative humidity

3.0 Installation

3.1 Digital Interface
3.1.1 The digital interface for the Model 225 is a DB-25 connector. The Model 225 may be ordered with either a male or a female connector. The gender of the connector is indicated by the first letter in the suffix of the model number. The Model 225M has a male connector and the Model 225F has a female connector.

3.2 Analog Interface
Note: The four-wire line between modems must be two twisted pairs. On each modem, the wires marked T+ and T- must be members of the same twisted pair, R+ and R- members of the other.
3.2.1 Screw Terminals - The Models 225 is supplied with 5 screw terminals marked T-, T+, G, R-, R+. When connecting two line drivers together the T+ of one unit goes to the R+ of the other, while T- goes to R-.
3.2.2 Phone Plug - The Model 225 are equipped with a standard RJ-11 modular phone connector. Only four of the six positions are used. The designation of the wires is shown in the following diagram.

4.0 Operation:

Connect the Model 225 to the device that contains the RS-232 port. The DTE/DCE slide switch on the Model 225 allows reversing of the input/output pins of the modem. When the switch is in the DCE position, pin 2 of the modem is an input to the modem.
The other slide switch on the modem is the RTS-Cont. This switch is used to allow the Request-To-Send (RTS) signal to control the transmitter when operating in a multi-dropped environment. For a standard point to point operation, the switch should be positioned in the "CONT" position. For multi-dropped operation, position the switch into the "RTS" position.

5.0 Troubleshooting:

The following is a list of possible problems that may arise during the installation:

1. The data being received is garbled?
a) the DTE/DCE slide switch is not set properly (see section 4).
b) the equipment that the Model 225 is connected to do not have the communication parameters set the same.
c) T+ and T- are reversed going to R+ and R-
d) one of the four wires is broken
e) wires are not paired properly: T+ and T- should be one twisted pair and R+ and R- are the other pair.

2. No data is being received.
a) customer equipment not connected to the 225.
b) the DTE/DCE switches are not set properly (see section 4).
c) one or more wires between the modems are open.
d) link connection exceeds maximum specified distance.

If the unit is believed to be defective, operation can be verified if one of the devices to which the modems are attached is capable of operating in a full duplex mode (such as a terminal or a PC using communications package such as Procomm). Connect the 225 to the terminal via the RS-232 connector and make the following loopback connections at the analog interface.

If the modem is functioning correctly, any data entered on the keyboard should appear on the screen.

6.0 Connector Pin Assignments:

7.0 Power:

The Model 225 can be powered in one of two ways. The first is that it attempts to derive positive power from Pins 4, 5, 6, 8 or 20 (if available) and negative power from the data input Pin (must be at least -5.5V in its quiescent state). The second is that if any devices that the 225 is connected to does not support any control signals, all power is then derived from the data input signal (must be at least -5.5V in the quiescent state).

8.0 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. 0315-0246/Rev. B