Marathon Computer AACC 2000 Wiring of 2-wire EIA-485 serial communications link

Marathon Monitors Inc.
AACC 2000 Carbon Nov. 1, 1997
21
Wiring of 2-wire EIA-485 serial communications link
Com
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.
A
B
PC
MMI Universial
Converter
RX
TX
Com
Com
TX
RX
Up to 32 S2000 controllers or
Interface Units may
be included on the network
232
Com
B
A
Com
A
B
Com
A
B
Com
A
B
Local Earth
Local
Ground
Zone 1
Local
Ground
Zone 2
Area 1
Com
A
B
E
F
D
Local
Earth
HE-
HF+
HD
Series 2000
Controller
HE-
HF+
HD
Series 2000
Controller
For reasons of safety
do not connect to
local earth here.
Local
Earth
Local
Earth
Local
Earth
Local
Earth
Local
Earth
HE -
HF+
HD
Series 2000
Controller
Galvanic
Isolation
Barrier
Local
Ground
Zone 1
Local
Ground
Zone 1
Local
Ground
Zone 1
Figure 1-9 EIA-485 wiring
2-wire EIA-485 is a connection which allows up to 32
controllers to be multi-dropped from a single
communications link over a distance of up to 1.2Km.
To ensure reliable operation of the communications
link, (without data corruption due to noise or line
reflections) the connections between the controller
should be made using a twisted pair of wires inside a
screened cable with the connections terminated with
resistors in the manner shown in this diagram.