Emerson DeviceNet Master Module IC694DNM200 Bus Length

LEDs and Connectors

The module's three DeviceNet-compliant LEDS show its operating and communications status.

The RS-232 serial port is used for a computer connection during firmware upgrades. The

DeviceNet connector is a removable spring-clamp terminal. It provides bus continuity and can

be removed from the module without disrupting bus operation.

The DeviceNet Bus

Devices can be connected directly to the trunk cable, or to drop lines that are joined to the trunk

cable with taps. Taps can be mounted in junction boxes or panels. Drop lines and daisy-chains

are often used inside control panels where multiple devices are grouped together.  When using

drops with daisy-chains and branches, the maximum length from a tap to its farthest drop is 20 feet.

Bus Length

The maximum length of the trunk cable and drops both depend on the cable type and data rate.

Individual drops may not exceed 6 meters and are limited to one network node per drop.

However, the node may have multiple ports.

For each baud rate, the total drop length is the sum of all the drop lines of both cable types in

the network.

In addition, if the distance from a tap to the most distant device on its drop is longer than the

distance from the tap to the nearest terminating resistor, the drop line length also counts as part

of the trunk cable length (as well as the overall drop length).

DeviceNet Cable

Either DeviceNet thick cable or thin cable can be used.  Thick cable permits greater cable

lengths and higher current levels. Generally, thick cable is used for the trunk cable.  Thin cable

is normally used for shorter distances and is suitable for drop cables and for installations where

more cable flexibility is needed. Both thick cable and thin cable are 5-wire, multi-conductor

copper cable.  Two wires form a transmission line for network communications. A second pair

transmits network power.  The fifth conductor forms an electromagnetic shield. Most cables

have color coded leads which correspond to the color coding on the terminals on the DeviceNet

Master Module.

Power Requirements

The DeviceNet Master module consumes 450mA at 5VDC (typical) from the PLC backplane.

This power is used for module operation, The DeviceNet Master powers its network transceiver

from the 24VDC DeviceNet network power source. Linear power supplies are recommended for

the DeviceNet power source. The DeviceNet power source should not also be used for device

power. Transients caused by  I/O devices can cause communications errors and even create

bus-off conditions.

The DeviceNet specification recommends using a power tap to connect a power supply to the

network. The power tap should be appropriately fused for the current capacity of the bus cables.

The maximum current on the network depends on the cable type.

The DeviceNet network power supply must be grounded, but only at one point.  The V- signal

must be connected to protective earth ground at the power supply only.  If multiple power

supplies are used, only one power supply must have V- connected to earth ground.

Current Limit for Thick Cable

For thick cable, the maximum current on the network is 16 Amps.  However, only 8 Amps is

permitted on a single network segment. 16 Amps can be drawn from a single power supply by

locating the power supply at the center point of two network segments, supplying 8 Amps to

each segment.

Current Limit for Thin Cable

For thin cable, the maximum current permitted is 3 Amps.