Omron CJ Series User Manual

2 Nomenclature and Installation
2-10
CJ-series PROFIBUS Master Unit Operation Manual for NJ-series CPU Unit (W509)
Note 1 If network extension beyond the range of the advised cable length is required, the use of
fibre optic cable to cross the larger distance should be considered.
2 The recommended minimum cable length is 1 m.
 Stub Lines
Passive Stub lines (branches from the main line) should be avoided for data transmission speeds of
more than 500 kbps. Except at end devices with termination, it is recommended to always use plug
connectors that permit two data cables to be connected directly to the plug. This method allows the
bus connector to be plugged and unplugged at all times without interrupting data communication
between other devices.
 Termination Resistors
In order to minimize cable reflections and ensure a defined signal level on the
data lines, the data transfer cable must be terminated at both ends with a termi-
nating resistor combination. The bus termination diagram is shown on the left.
The bus terminator connects the two data lines via a 220 Ω resistor which, in
turn, is connected to VP 5VDC and DGND via two 390 Ω resistors. Powering
the terminator resistor via VP 5V and DGND ensures a defined idle state poten-
tial on the data lines.
To ensure the correct functioning up to the highest baud rate, the bus cable
must be terminated at both its ends.
A missing bus termination can cause errors during data transfer. Problems can
also arise if too many bus terminators are fitted, since each bus terminator rep-
resents an electrical load and reduces the signal levels and thus the signal-to-
noise ratio. Too many or missing bus terminators can also cause intermittent
data transfer errors, particularly if the bus segment is operated close to the
specified limits for maximum numbers of devices, maximum bus segment
length and maximum data transfer rate.
In addition to the bus termination, additional precautions must be taken to
ensure proper operation at high baud rates, i.e. baud rates of 500 kbps and
higher. Due to the capacitive load of the device and the resulting cable reflec-
tions, bus connectors must be provided with built-in series inductors, of 110 mH
each, as shown in the figure on the left.
Installing the inductors applies to all devices on the network, and not only to the
devices at both ends of the bus cable.
Baud Rate
(kbps)
Distance/segment
(m)
9.6 1200
19.2 1200
45.45 1200
93.75 1200
187.5 1000
500 400
1500 200
3000 100
6000 100
12000 100
2-3-2 Bus Termination
390 Ω
390 Ω
220 Ω
VP
B-Line
A-Line
DGND
Networ
k
B-Line
A-Line
110 mH
110 mH
Network

Omron CJ Series Specifications

General

Brand	Omron
Model	CJ Series
Category	Controller
Language	English