Marathon Monitors Inc.

Wiring of 2-wire EIA-485 serial communications link

 

PC

 

 

 

2-wire EIA-485 is a connection which allows up to 32

Com

TX

controllers to be multi-dropped from a single

RX

Local

 

communications link over a distance of up to 1.2Km.

 

To ensure reliable operation of the communications

Earth

 

232

 

link, (without data corruption due to noise or line

 

reflections) the connections between the controller

 

 

Local

 

should be made using a twisted pair of wires inside a

 

screened cable with the connections terminated with

Earth

RX

Com

TX

 

 

resistors in the manner shown in this diagram.

MMI Universial

 

Converter

Com

B

A

 

A

HE -

 

 

 

 

 

B

Series 2000

 

 

 

 

HF+

 

 

 

 

Com

Controller

 

 

 

 

HD

 

 

 

 

 

 

 

 

 

Local

 

 

 

 

 

 

Earth

 

 

 

 

 

 

Local

 

 

Local

Local

 

 

Ground

 

 

Ground

Ground

 

 

Zone 1

 

 

 

 

 

 

Zone 1

Zone 2

 

 

 

 

 

 

 

Local

 

 

A

 

 

 

Earth

A

 

A

HE-

 

Galvanic

B

Series 2000

 

B

B

 

Local

Isolation

HF+

 

 

Controller

Ground

Com

Barrier Com

Com

 

HD

 

Zone 1

 

 

 

 

 

Local

 

 

 

 

Earth

 

 

 

Local Earth

Local

 

 

 

 

Ground

 

 

 

 

Zone 1

Up to 32 S2000 controllers or

For reasons of safety

 

do not connect to

 

Interface Units may

 

Local

be included on the network

 

local earth here.

Earth

 

 

 

 

 

A

HE-

Series 2000

 

 

B

 

 

HF+

 

 

Com

F

Controller

 

Area 1

HD

 

 

 

 

 

Note:

All resistors are 220 ohm 1/4W carbon composition.

Local grounds are at equipotential. Where equipotential is not available wire into separate zones using a galvanic isolator.

Use a repeater (KD845) for more than 32 units.

Figure 1-9 EIA-485 wiring

AACC 2000 Carbon

21

Nov. 1, 1997

 

 

Page 21
Image 21
Marathon Computer AACC 2000 manual Wiring of 2-wire EIA-485 serial communications link, EIA-485 wiring