Diagnostic Functions - Omron WS02-9094G - V1.0 Operation Manual

Overview of PROFIBUS
Token Passing
Polling Procedure
Multi-peer Communication
Broadcast
Communication
Multicast Communication
1-1-5

Diagnostic functions

Extensive Diagnostics
Device Related
Diagnostics
Module Related
Diagnostics
Channel Related
Diagnostics
The token passing procedure guarantees that the bus access right (the token)
is assigned to each master within a precisely defined time frame. The token
message, a special message for passing access rights from one master to the
next master, must be passed around the logical token ring - once to each
master - within a specified target rotation time. Each master executes this pro-
cedure automatically.
The polling or master-slave procedure permits the master, currently in pos-
session of the token, to access its assigned slaves. The figure below shows a
possible configuration The configuration shows three active devices (masters)
and six passive devices (slaves).
DPM1
Active stations
Master devices
Passive stations
Slave devices
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 mas-
ter-slave communication relationship, and a DPM2 master can take the initia-
tive to communicate with DPM1 master devices in a master-master
communication relationship.
In addition to logical peer-to-peer data transmission, PROFIBUS DP provides
multi-peer communication (broadcast and multicast).
In the case of broadcast communication a master device sends an unac-
knowledged message to all other devices (masters and slaves).
In the case of multicast communication a master device sends an un-acknowl-
edged message to a predetermined group of slave devices.
Extensive diagnostic functions defined in PROFIBUS DP enable the fast loca-
tion of error at slave devices. Diagnostic messages are transmitted over the
bus and collected at the master. Three diagnostic message types are defined:
• Messages concerning the general operational status of the whole device,
e.g. over temperature, low voltage.
• Messages indicating that an error is present in a specific I/O range of a
device, e.g. an 8-bit output module.
• Messages indicating an error at a given input or output, e.g. short circuit
on Output 5.
Token Passing
DPM2
Polling
Section 1-1
DPM 1
PROFIBUS
5