LDM485
Fully Isolated
Limited Distance Modem,
RS-232/485 Converter
Description
Features
The LDM485 is a compact RS-232 to RS-485 converter which features
a complete electrical isolation barrier and heavy duty electrical surge
protectors. These devices feature a rugged aluminum enclosure small
enough to mount on the back panel of typical computer equipment,
saving valuable desk and floor space. Isolation is provided by optical
couplers and a DC-to-DC converter. The RS-232 connection is through
male or female EIA 25-pin connectors. The RS-485 connections are
made through convenient solderless screw terminals.
Á COMPLETE ISOLATION WITH OPTICAL COUPLERS
AND POWER DC-TO-DC CONVERTER
Á INDUSTRIAL SURGE PROTECTION DEVICES
Á SIX LED DIAGNOSTIC INDICATORS
Á 19.2K BAUD AT 3 MILES (5KM), 57.6K BAUD AT 0.5
MILES (0.8KM)
The LDM485 series is designed for full duplex operation over two-
wire pairs. Outputs are tri-state, allowing multidropping of up to 64
units. Hardware handshake is available over two separate wire pairs.
Data rates are DC to 57.6k baud. Six diagnostic LED indicators are
provided (see Figure 1) for installation guidance and system
troubleshooting. The RS-232 interface supports Request To Send,
Clear To Send, Data Set Ready, Received Line Signal Detect, and
Data Terminal Ready. A convenient null modem switch is provided for
the data lines. Also, a line termination switch connects a line
termination resistor and line bias resistors to the RS-485 receive lines.
The RS-485 interface supports Request To Send and Clear To Send
on separate wire pairs. The LDM485 may be used to convert two sets
of send and receive channels by using RTS and CTS circuits as the
second data channels. Data rates are the same. The units use 12VAC
from a wall-mounted transformer to screw terminals 1 and 2 on the
RS-485 connector. Alternately, they can use ± 12VDC to pins 9 (+ )
and 10 (–) of the RS-232 connector.
Á REQUEST-TO-SEND, CLEAR-TO-SEND HANDSHAKE
Á TRI-STATE OUTPUTS FOR MULTIDROP
APPLICATIONS, UP TO 64 DEVICES
Á SELECTION OF CONNECTORS
Á WIDE OPERATING TEMPERATURE RANGE
Á SOLDERLESS SCREW TERMINAL FIELD
CONNECTIONS
Dataforth does not authorize or warrant its products for use in life support/critical applications.
Model
Channel Lines(2)
Control Lines(2)
LDM485
TD, RD, RTS, CTS
RTS, CTS, DTR, DSR, RLSD
1 (Reverses RS-232 pins 2 and 3)
60mA max/output
Null Modem Switch
RS-485 Output Drive
RS-485 Input Impedance
Power:
Specifications
12kΩ min/input
Model
LDM485
(3)
AC operation
12VAC, ± 10%, 10W screw terms 1 & 2
+ 11.5 to + 17VDC @ 500mA on pin 9
-11.5 to -17VDC @ 100mA on pin 10
Baud Rate Range
0 – 57.6K
DC operation
Operating Environment
Dimensions
Baud Rate
Distance (miles)(1)
Distance (km)
57.6K 38.4K 19.2K 9.6K 4.8K 2.4K – 0
0.5
0.8
1
1.7
3
5
4
5
8
13.3
0°C to + 70°C, 0-95% relative humidity,
noncondensing
6.7 8.3
Wire Capacitance
Equal to 25pF per foot and up to 32 multidrop units
64
6.6 in x 2.1 in x 1.28 in
Maximum Multidrop Units
(167.6 mm x 53.3 mm x 32.5 mm)
Common Mode
Isolation
Surge: 1500V
Continuous: 1000V
Weight
PT3, PT3E
7 oz (200 g) max
11.0 oz (311.8 g) max
Differential Mode
Surge Protection
(9 devices)
(AC input)
ANSI/IEEE C37.90.1-1989
(all RS-485 inputs and outputs)
(4)
MTBF
> 100,000 hrs
Notes: (1) Distances reduced if multidropping more than 32 units; by 30% for 33-48 units, 50% for 49-
64. (2) TD = Transmit Data, RD = Receive Data, RTS = Request To Send, CTS = Clear To Send, DTR =
Data Terminal Ready, DSR = Data Set Ready, RLSD = Received Line Signal Detect. (3) 120VAC and 220
VAC power transformers are available. (4) Ground-benign environmental conditions (no salt atmosphere,
< 50°C ambient temperature).
Modes
Asynchronous 4-wire duplex, 2-wire half-duplex,
2-wire simplex
22
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