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

		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