Black Box 202T User Manual

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© 2007. All rights reserved. Black Box Corporation.

Modem 202 and Modem 202T

Reliable old favorites, manufactured to today’s exacting specifications.


Compatible with the Bell 202T standard.

Operate over 2- or 4-wirevoice-gradeleased or private lines.

For point-to-pointorpoint-to-multipointpolling networks.

Prevent data and carrier-detecterrors over noisy lines.


Choose between ACand DC-poweredModem 202T models.

An industrial application for the Modem 202.




Modem 202



Modem 202


Modem 202







































Programmable logic



Dedicated wire



Dedicated wire

























































































































































telemetry unit

Water tank

telemetry unit

Water tank

telemetry unit

Water tank





















Back in the day, Bell 202 was the top-speedmodem standard, boasting1200-bpsrates that were four times faster than the poky Bell 108 standard. Still widely used in many industries, Bell 202 modems like our Modem 202 or Modem 202T keep data moving along. Order one of these modems to expand an existing industrial, System Control and Data Acquisition (SCADA), or metering application, or to replace an old UDS/Motorola® 202T Modem. In fact, the Modem 202T is apin-for-pin,form, fit, and function replacement for thattried-and-truemodem. Just think what it can do for your legacy system!

The Modem 202 (MD845A-R2)and the Modem 202T (MD1970A,MD1970A-DC)function the same way. However, the Modem 202 supports speeds up to 1200 bps over unconditioned lines; the Modem 202T supports speeds up to 1800 bps over conditioned lines.

Widely installed and a prerequisite for many leased-lineapplications, both the Modem 202 and the Modem 202T supportvoice-bandfrequency shift keyed (FSK) modulation within asynchronouspoint-to-pointor multipoint systems that usevoice-grade2-wire,half-duplexor4-wire,full duplex dedicated or leased lines. These can be loaded or unloaded circuits, equal to or better than the ITU (formerly CCITT) M.1020/1025 or Bell 3002 leased lines.

These modems have many uses.

You can use a Modem 202 or Modem 202T with remote terminal units (RTUs) and programmable logic controllers (PLCs) to control and monitor a large number of remote devices—trafficcontrol lights, for instance. In addition to SCADA applications, the modems are quite useful for

temperature and pressure controllers in numerous industries, particularly those in which you expect to add automated devices.

The water-treatmentindustry prefers the Modem 202 because it’s compatible with battery systems from 11 to 18 VDC. The Modem 202 is also relied upon heavily by the U.S. Government for daily commerce.

Noisy lines aren’t a problem either. The Modem 202 and the Modem 202T have circuitry that prevents data errors that occur on such lines, particularly those within multidrop systems where carrier turn-offsand other modems on the same line can cause noise spikes and other harmful high frequencies. The modems combinesoft-carriergeneration andsoft-carrierdetection as well as asignal-noise-ratio(SNR) detector to eliminate suchline-noiseerrors.

The modems also have antistreaming features, which prevent them from remaining in Transmit Mode when they’re not actively transmitting data. Great for multipoint applications, antistreaming prevents a malfunctioning

slave modem from occupying the line indefinitely. When antistreaming is active, the Modem 202 or Modem 202T can only transmit data for up to 56 seconds. Then, they automatically turn off their transmitter and look for an ON-to-OFFtransition of Request To Send (RTS) before proceeding with normal operation.

Modem 202T offers diagnostic testing features.

For testing purposes, the Modem 202T has a five-positionrotary switch on its front panel for running analog and digital loopbacks as well asself-tests.To verify the transmitter and receiver of the local modem and its connection to a local DTE,



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generate a data pattern from the locally attached DTE or have the modem generate a test pattern.

You can also run line and modem tests to verify the integrity of the line between the local and remote modems. With this test, the local Modem 202T loops back received data to the transmitter and sends the data to the remote modem. These characters can be done by using a modem test pattern or by originating a data pattern from the local DTE.

Configuration is simple!

To configure the Modem 202T, just set a few DIP switches. These jumper settings control operating characteristics such

as the dynamic range of the modem receiver, the transmit level, and the call turnaround squelch (which guards against echoes

from already-completedtransmissions).

MD845A-R2 By default, the Modem 202T’s DIP switches are set for4-wire,full duplex operation. To reconfigure the modem for2-wire,halfduplex applications, just change the jumper settings.

When configured for 4-wire,full duplex operation, the modem can be strapped to transmit data to corresponding slave modems with no RTS to Carrier Turnoff Signal (CTS) delay, which is ideal for minimizing turnaround. To increase the modem’s turnaround time, just configure it for2-wire,half-duplexoperation. This will enable the modem to encounter anRTS-to-CTS delay when transmitting to its slave modems.

On the inside of the Modem 202T is a simple three-positionheader for full orhalf-duplexmode. The device’s DCE interface quickly connects to any device equipped with a standard DB9 or DB25 connector.

Troubleshooting’s easy, too.

An LED control display enables you to confirm modem operation at a glance, and a local and remote test switch enables verification of the link’s integrity.

Along with the Modem 202 or Modem 202T, you’ll receive a cable for making RJ-45to4-wireleased-lineconnections. But to connect a data terminal, you’ll need anRS-232cable.



Distance (Maximum) — 20 mi. (32.2 km) on unloaded lines, depending upon line characteristics

Enclosure — Standard NEMA 1;18-gaugesteel with mounting flangesHandshake Modes — DataSense (DSCC) or RTS line

Mounting — Hole pattern14"(0.6-cm)diameter located on rectangle 8.3" x 2.8" (21.1 x 7.1 cm)

Operating Frequency — 1200/2200 Hz (Bell 202 or 1300/2100 ITU V.35) FSK (Frequency Shift Key)

Operation — 2-wire,half-duplexor4-wire,full duplexProtocol — Asynchronous

Speed — 300, 600, or 1200 baud halfor full duplex up to 1200 baud simplex

Connectors — (2) terminal blocks, (1) DB9 F

Indicators — (4) LEDs: Data Out, Data In, Carrier, PowerTemperature Tolerance — -4to +158°F(-20to +70°C)Power — Input: 11 to 18 volts DC at a minimum of 200 mA;

External wallmount power supply provided for 110 VAC nominal Size — 1.5"H x 5"W x 9"D (3.8 x 12.7 x 22.9 cm) over mounting flanges

MD1970A and MD1970A-DC:

Carrier Detect Delay — 6 or 23 msOFF-to-ON,6ON-to-OFF

Carrier Frequencies — Mark: 1200 Hz ± 1%; Space: 2200 Hz ± 1%

Diagnostics — Self-test,analog loopback, digital loopback, test pattern transmit

Line Impedance — 600 ohms ± 10% transformer coupled and transient protected

Modulation — Phase coherent; frequency shift keyed (FSK)Operation — 2-wire,half-duplexor4-wire,full duplexProtocol — Asynchronous

RTS to CTS Delay — 8, 33, 59, or 219 ms

Speed (Maximum) — Unconditioned line: 1200 bps; Conditioned line: 1800 bps

Transmitter Output Level — Selectable from 0 to-14dBm in2-dBsteps

Turnaround Squelch — 8 ms or 159 ms

Connectors — (1) DB25 female (DTE); (1)RJ-45(telco)Indicators — (7) LEDs: RS, CS, CD, RD, TD, TM, PowerTemperature Tolerance — -40to +185°F(-40to +85ºC)Humidity Tolerance — Up to 95%, noncondensingPower — MD1970A: 115 VAC, 60 Hz;

MD1970A-DC:12 to 60 VDC

Size — 2.3"H x 7"W x 9.6"D (5.8 x 17.8 x 24.4 cm)





User‘s manual


202T Modem Rackmount Card

User‘s manual





Modem 202 (without Diagnostics)



Modem 202T Standalone (with Diagnostics)











Rackmount Card


You may also need…



DB9 Extension Cable


DB9 Male to DB25 Female Adapter




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