8/12/2019 RS-485 ligao a 2 ou 3 fios.pdf

1/3

Ohio Semitronics, Inc. Page 1 of 3 Communication Connections

4242 Reynolds Drive For the Surface Mount Version

Hilliard, Ohio 43026 of the Digital Load Monitor

Phone: 614-777-1005 E-mail sales@ohiosemi.com

Connecting Multiple Digital Load Monitors to anRS-485 or RS-422 System

This paper applies to the surface mount version of the Digital Load Monitors, which have a barrier strip with 6

terminals to attach the communications cable.

The connection positions are:

+5 volts DC this is for the OSI IFC-4498A RS-422 to RS-432 converter only.

Common this is for the OSI IFC-4498A RS-422 to RS-432 converter only.

Tx+ Transmit +

TX- Transmit -

Rx+ Receive +

Rx- Receive -

If you are using the IFC-4498A RS-422 to RS-232 converter to connect to a COM port on your computer, theleads are labeled +5V, Com, Tx+, Tx-, Rx+, and Rx-. Connect these leads to the matching terminals on the

Digital Load Monitor (DLM) closest to your computer. The terminals labeled +5V and Com are used to supply

the converter with the required operating voltage. The 5V and Com should be connected only on the DLM that

is connected to the IFC-4498A. All other DLM meters should have these terminals open (no connection).

When using the IFC-4498A, a four-wire connection must be used (plus the power supply leads).

Note: The RS-485 standard was developed jointly by the Electronic Industries Association (EIA) and the

Telecommunications Industry Association (TIA). The EIA once labeled all of its standards with the prefix "RS"

(Recommended Standard). Many of us still use this designation but the TIA and EIA have officially replaced

the "RS" with "EIA/TIA" to help identify the origin of the standard.

Recommendations:

For RS-422 / RS-485 four-wire use two twisted pairs of 24AWG wires. One pair is for Tx+ and Tx- and the

second pair is for Rx+ and Rx-.

For RS-485 two-wire applications use one twisted pair of 24AWG wire.

Essential for minimizing reflections in two-wire systems are termination resistors. These should be 120-ohm

resistors at both ends. Many RS-485 ports already include the host end resistor. Check the instructions for the

port.

Maximum loads (DLMs) on a 4-wire system is 10.

Maximum loads (DLMs) on a 2-wire system is 32.

Each Digital Load Monitor on a two or four wire system must have a separate 4-digit address. The user may

assign the address using the software supplied with these meters.

8/12/2019 RS-485 ligao a 2 ou 3 fios.pdf

2/3

Ohio Semitronics, Inc. Page 2 of 3 Communication Connections

4242 Reynolds Drive For the Surface Mount Version

Hilliard, Ohio 43026 of the Digital Load Monitor

Phone: 614-777-1005 E-mail sales@ohiosemi.com

+5V COM Tx+ Tx- Rx+ Rx- +5V COM Tx+ Tx- Rx+ Rx-+5V COM Tx+ Tx- Rx+ Rx-

Tx+ Tx- Rx+ Rx-

DLM Surface Mount

Version

DLM Surface Mount

Version

DLM Surface Mount

Version

Host RS-422 or RS-485

To additional DigitalLoad Monitors orother RS-422 Devices

if there are any.

+5V COM Tx+ Tx- Rx+ Rx- +5V COM Tx+ Tx- Rx+ Rx-+5V COM Tx+ Tx- Rx+ Rx-

DLM Surface Mount

Version

DLM Surface Mount

Version

DLM Surface Mount

Version

To additional DigitalLoad Monitors orother RS-485 Devicesif there are any.

Connecting multiple surface mount Digital Load

Monitors to a host with an RS-422 or RS-485 input.

4 Wire Connect ion

Connecting multiple surface mount Digital LoadMonitors to a host with an RS-485 input.

2 Wire Connect ion

Tx+ Tx- Rx+ Rx-

Host RS-485

120-ohm resistoron the last DLM.

8/12/2019 RS-485 ligao a 2 ou 3 fios.pdf

3/3

Ohio Semitronics, Inc. Page 3 of 3 Communication Connections

4242 Reynolds Drive For the Surface Mount Version

Hilliard, Ohio 43026 of the Digital Load Monitor

Phone: 614-777-1005 E-mail sales@ohiosemi.com

IFC-4498ARS-422 to RS-232

Converter.

+5V CO M Tx+ Tx- Rx + Rx - +5V CO M Tx+ Tx- Rx+ Rx -+5V CO M Tx+ Tx- Rx + Rx -

DLM Surface Mount

Version

DLM Surface Mount

Version

DLM Surface Mount

Version

To addit ional DigitalLoad Monitors orother RS-422 Devicesif there are any.

Connecting multiple surface mount Digital Load

Monitors to a host with using the OSI IFC-4498A

RS-422 to RS-232 converter.

Cable to the COMPort on a personal

computer.

+5 V CO M Tx + Tx- Rx+ Rx -

If you have any questions regarding the connections or use of the Ohio Semitronics, Inc. Digital Load Monitors

(DLM), please contact us at Ohio Semitronics, Inc.

There is a manual available that describes using these meters and that describes the communications protocol.If you require one of these manuals, please call or e-mail us.

August 3, 2001