T-Branch Tap Connections; Connecting Devices Other Than Devicenet Products; Connecting Terminators (Terminating Resistors) - Omron DEVICENET Operation Manual

Network Configuration
2-2-5

T-branch Tap Connections

2-2-6

Connecting Devices other than DeviceNet Products

2-2-7

Connecting Terminators (Terminating Resistors)

What is a Terminating
Resistor?
Operation without
Terminating Resistors
Operation with Too Many
Terminating Resistors
40
The single-branch T-branch Taps (3 connectors) can be used to make a
branch from the trunk line or a branch line. It isn't necessary to connect the
paired connectors to the trunk line. Likewise, there is no restriction on the use
of connectors in a three-branch T-branch Tap. The connectors can connect to
the trunk line or branch lines.
Trunk
Trunk
line
line
Branch line
Both configurations
are acceptable.
Although there is no restriction on the use of connectors in the T-branch Taps,
as a rule we recommend using the paired connectors for the trunk line so that
the trunk line is easy to identify.
Do not connect devices that are not DeviceNet products because incompati-
ble devices can cause signal reflection or attenuation and interfere with nor-
mal network communications.
A Terminating Resistor (commonly known as a terminator) is a resistor con-
nected to the end of the trunk line to absorb the signals sent through the net-
work, dissipating the signals as heat and preventing them from bouncing back
into the network. A Terminating Resistor is required at each end of the net-
work (trunk line).
Note Terminating resistors are not built into DeviceNet devices.
The DeviceNet network will not function properly without Terminating Resis-
tors. Communications errors will occur, such as remote I/O communications
errors and communications timeouts.
The signals in a DeviceNet network are comparable to surface waves on
water. When a stone is dropped in a bucket of water, circular waves ema-
nate from the stone and run into the sides of the bucket and the reflected
waves interfere with the waves coming from the center. As a result, the
waves from the center become distorted.
The same principle applies to the digital signals in a DeviceNet network.
When the digital signals (waves) passing through the network reach the
end of the network, the bounce back and interfere with the signals (waves)
emanating from the DeviceNet Master (center) of the network.
The Terminating Resistors absorb the digital signals at the ends of the net-
work so that they do not bounce back and distort the signals from the Mas-
ter.
If Terminating Resistors are attached at all T-branch Taps within the network,
the digital communications signals will be absorbed midway through the net-
work and the network will not function normally. Communications errors will
occur, such as remote I/O communications errors and communications time-
outs.
Trunk
Branch Trunk
line line
line
Trunk line Branch lines
Section 2-2
Trunk Branch
Branch
line line
line
Trunk
Branch Trunk
line
line line
Both configurations
are acceptable.