1 Features and System Configuration
1-4
CJ-series PROFIBUS Master Unit Operation Manual for NJ-series CPU Unit (W509)
RS-485 Transmission Speed
Transmission speeds between 9.6 kbps and 12 Mbps can be selected as shown in the table below.
One unique transmission speed must selected for all devices on the bus when the system is com-
missioned.
Cable Length
The maximum cable length values depend on the transmission speed and are based on type-A
cable (see Cable Type on page 9). The length can be increased by the use of repeaters. However, it
is not recommended to use more than three repeaters in series in a PROFIBUS network.
PROFIBUS distinguishes between master devices and slave devices.
Master Devices
Master devices determine the data communication on the bus. A Master can send messages with-
out an external request, as long as it holds the bus access right (the token). Masters are also
referred to as active devices in the PROFIBUS standard.
Class 1 Master (DPM1)
A PROFIBUS DP Class 1 Master (DPM1) device is a central controller, which exchanges informa-
tion with the decentralized devices (i.e. DP slaves) within a specified message cycle.
Class 2 Master (DPM2)
PROFIBUS DP class 2 Master (DPM2) devices are programmers, configuration devices or operator
panels. They are used during test runs, for configuration of the DP system, or for operation and
monitoring purposes.
As of Unit Version 3.0, the CJ1W-PRM21 is a PROFIBUS DP Class 1 as well as Class 2 Master
device.
Slave Devices
Slave devices are peripheral devices. Typical slave devices include input/output devices, valves,
drives, and measuring transmitters. They do not have bus access rights and they can only acknowl-
edge received messages or send messages to the master when requested to do so. Slave devices
are also called passive devices.
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
1-1-3 Device Types
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