1 Features and System Configuration
1-6
CJ-series PROFIBUS Master Unit Operation Manual for NJ-series CPU Unit (W509)
The three masters form a logical token ring. When an active device receives the token message, it
can perform its master role for a certain period of time. During this time it can communicate with all
assigned slave devices in a master- slave communication relationship, and a DPM2 master can take
the initiative to communicate with DPM1 master devices in a master-master communication relation-
ship.
Multi-peer Communication
In addition to logical peer-to-peer data transmission, PROFIBUS DP provides multi-peer communi-
cation (broadcast and multicast).
Broadcast Communication
In the case of broadcast communication a master device sends an unacknowledged message to all
other devices (masters and slaves).
Multicast Communication
In the case of multicast communication a master device sends an unacknowledged message to a
predetermined group of slave devices.
Extended Diagnostics
Extended diagnostic functions defined in PROFIBUS DP enable the fast location of error at slave
devices. Diagnostic messages are transmitted over the bus and collected at the master. Three diag-
nostic message types are defined:
• Device Related Diagnostics: Messages concerning the general operational status of the
whole device, e.g. over temperature, low voltage.
• Module Related Diagnostics: Messages indicating that an error is present in a specific I/O
range of a device, e.g. an 8-bit output module.
• Channel Related Diagnostics: Messages indicating an error at a given input or output, e.g.
short circuit on Output 5.
1-1-5 Diagnostic functions
DPM1 DPM2 DPM1
Token Passing
Polling
PROFIBUS
Passive stations
Slave devices
Active stations
Master devices
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