Network Structure, Biasing, And Termination Resistance; Rs485 Networking; Terminating And Biasing An I/O Networks And Modbus Networks - Emerson E2 Einstein Manual

6 Network Structure, Bi-
asing, and Termina-
tion Resistance

6.1. RS485 Networking

The RS485 Input/Output (I/O) Network connects
all input and output communication boards together
in a single open communications loop. This loop, or
"daisy chain," connects the E2 to multiple input and
output communication boards, and terminates at the
last input or output board on the network. A diagram
of this network arrangement is shown in Figure 6-1.
Figure 6-1 - I/O Network Configurations
Daisy chains are the only allowable network
structure for CPC RS485 I/O networks. Branching
and "star configurations" can seriously affect net-
work performance and therefore are not allowed.
6.1.1. Terminating and Biasing an
I/O Networks and MODBUS
Networks
Proper termination and biasing is an important
part of reducing I/O network noise. All CPC-manu-
factured devices with RS485 ports are equipped with
three on-board jumpers that can provide the resis-
tance necessary to terminate and bias the network
endpoint. The middle jumper provides the termina-
tion resistance, while the two outside jumpers pro-
vide biasing.
RS485 Networking
I/O Network daisy chains must be terminated
AND biased at both ends of the daisy chain (Figure
6-2).
MODBUS daisy chains must be terminated at
both ends of the daisy chain, but must only be biased
at ONE end. Biasing the E2 is the preferred method
of network biasing. Most third-party MODBUS
devices have no termination or network bias capabil-
ities and will require use of a MODBUS termination
block (see Section 6.1.1.1., MODBUS Termination
Blocks). Others, like the Control Link, have three
jumpers similar to CPC I/O devices. For these
devices, set the termination jumper (middle) to the
UP position and leave the biasing jumpers in the
DOWN position. (Figure 6-2)
RS485 I/O NETWORKS
MODBUS NETWORKS
TERMINATED & BIASED
(ALL 3 JUMPERS SET
TO "UP" POSITION)
Figure 6-2 - I/O Network and MODBUS Termination and
Biasing
6.1.1.1. MODBUS Termination Blocks
Third-party devices may or may not have on-
board termination jumpers — consult the manufac-
turer's instructions for termination information.
Network Structure, Biasing, and Termination Resistance • 7
TERMINATED & BIASED
(ALL 3 JUMPERS SET
TO "UP" POSITION)
TERMINATED, NO BIAS
(MIDDLE JUMPER SET
TO "UP" POSITION)
OR USE MODBUS
TERMINATION BLOCK