Reliable old favorites, manufactured
to today’s exacting specifications.
Reliable old favorites, manufactured
to today’s exacting specifications.
Modem 202 and Modem 202T
© 2007. All rights reserved. Black Box Corporation.
FREE 24-hour Tech Support: 724-746-5500
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FEATURES
• Compatible with the Bell 202T standard.
• Operate over 2- or 4-wire voice-grade
leased or private lines.
• For point-to-point or point-to-multipoint
polling networks.
• Prevent data and carrier-detect errors
over noisy lines.
• Anti-streaming capability.
• Choose between AC- and DC-powered
Modem 202T models.
An industrial application for the Modem 202.
OVERVIEW
Back in the day, Bell 202 was the top-speed modem
standard, boasting 1200-bps rates 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 a pin-for-pin, form, fit, and function replacement for that
tried-and-true modem. 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-line
applications, both the Modem 202 and the Modem 202T
support voice-band frequency shift keyed (FSK) modulation
within asynchronous point-to-point or multipoint systems
that use voice-grade 2-wire, half-duplex or 4-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—traffic control 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-treatment industry 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-offs and other modems on the
same line can cause noise spikes and other harmful high
frequencies. The modems combine soft-carrier generation
and soft-carrier detection as well as a signal-noise-ratio (SNR)
detector to eliminate such line-noise errors.
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-OFF
transition 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-position
rotary switch on its front panel for running analog and digital
loopbacks as well as self-tests. To verify the transmitter and
receiver of the local modem and its connection to a local DTE,
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Programmable logic
controller
Water tank
Water tank
Water tank
Remote
telemetry unit
(RTU)
Remote
telemetry unit
(RTU)
Remote
telemetry unit
(RTU)
Modem 202
(MD845A-R2)
Modem 202
(MD845A-R2)
Modem 202
(MD845A-R2)
RS-232
cable
Dedicated wire
pair(s)
Dedicated wire
pair(s)
RS-232
cable
RS-232
cable
RS-232
cable
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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-completed transmissions).
By default, the Modem 202T’s DIP switches are set for 4-wire,
full duplex operation. To reconfigure the modem for 2-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 for 2-wire, half-duplex
operation. This will enable the modem to encounter an RTS-toCTS delay when transmitting to its slave modems.
On the inside of the Modem 202T is a simple three-position
header for full or half-duplex mode. 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-45 to 4-wire leased-line connections.
But to connect a data terminal, you’ll need an RS-232 cable.
MD845A-R2
TECH SPECS
MD845A-R2:
Distance (Maximum) — 20 mi. (32.2 km) on unloaded lines,
depending upon line characteristics
Enclosure — Standard NEMA 1; 18-gauge steel with mounting flanges
Handshake Modes — DataSense (DSCC) or RTS line
Mounting — Hole pattern
1
⁄4" (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-duplex or 4-wire, full duplex
Protocol — Asynchronous
Speed — 300, 600, or 1200 baud half- or full duplex up to
1200 baud simplex
Connectors — (2) terminal blocks, (1) DB9 F
Indicators — (4) LEDs: Data Out, Data In, Carrier, Power
Temperature Tolerance — -4 to +158°F (-20 to +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 ms OFF-to-ON, 6 ON-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-duplex or 4-wire, full duplex
Protocol — 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 -14 dBm in 2-dB steps
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, Power
Temperature Tolerance — -40 to +185°F (-40 to +85ºC)
Humidity Tolerance — Up to 95%, noncondensing
Power — 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)
MD845A-R2, MD1970A, MD1970A-DC:
✦
Modem
✦
RJ-45 to 4-wire leased-line cable
✦
User‘s manual
MD1970C:
✦
202T Modem Rackmount Card
✦
User‘s manual
WHAT‘S INCLUDED
Item Code
Modem 202 (without Diagnostics) MD845A-R2
Modem 202T Standalone (with Diagnostics)
Standalone
AC MD1970A
DC MD1970A-DC
Rackmount Card MD1970C
You may also need…
DB9 Extension Cable EDN12H-0010-MF
DB9 Male to DB25 Female Adapter FA521A-R3
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