22

®

LDM485

Fully Isolated

Limited Distance Modem,

RS-232/485 Converter

Description

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.

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.

Specifications

Model

LDM485

Baud Rate Range

0 – 57.6K

Baud Rate

57.6K 38.4K 19.2K

9.6K

4.8K 2.4K – 0

0.513

45

8

Distance (km)

0.8

1.7

5

6.7

8.3

13.3

Wire Capacitance

Equal to 25pF per foot and up to 32 multidrop units

Maximum Multidrop Units

64

Common Mode

Surge: 1500V

Isolation

Continuous: 1000V

Differential Mode

(AC input)

Surge Protection

ANSI/IEEE C37.90.1-1989

(9 devices)

(all RS-485 inputs and outputs)

Modes

Asynchronous 4-wire duplex, 2-wire half-duplex,

2-wire simplex

Model

LDM485

TD, RD, RTS, CTS

RTS, CTS, DTR, DSR, RLSD

Null Modem Switch

1 (Reverses RS-232 pins 2 and 3)

RS-485 Output Drive

60mA max/output

RS-485 Input Impedance

12k

Ω min/input

Power:

12VAC, ±10%, 10W screw terms 1 & 2

DC operation

+11.5 to +17VDC @ 500mA on pin 9

-11.5 to -17VDC @ 100mA on pin 10

Operating Environment

0

°C to +70°C, 0-95% relative humidity,

noncondensing

Dimensions

6.6 in x 2.1 in x 1.28 in

(167.6 mm x 53.3 mm x 32.5 mm)

Weight

7 oz (200 g) max

PT3, PT3E

11.0 oz (311.8 g) max

>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).

Dataforth does not authorize or warrant its products for use in life support/critical applications.

Features

AND POWER DC-TO-DC CONVERTER

MILES (0.8KM)

APPLICATIONS, UP TO 64 DEVICES

CONNECTIONS