PROFIBUS DP-Master

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5.2 Profibus DP Operation Modes (States)
A Profibus DP master can be in one of four different states, which are called the operation modes and
have a different degree of allowed functionality. These states and their symbolic names are:
• OFFLINE (USIF_OFFLINE)
• STOP (USIF_STOP)
• CLEAR (USIF_CLEAR)
• OPERATE (USIF_OPERATE)
These states differ in the degree of allowed functionality as follows:
• In OFFLINE state, there is no communication (data transfer) permitted at all. This is the state
after initialization. This means, the master is waiting for a signal to start and does not participate
in the token ring of the Profibus access control mechanism.
• In STOP state, there is no data transfer permitted between master and slaves. Data transfer to
other masters in multi-master system is allowed, however. The bus parameter set has been
loaded successfully in order to get into STOP state.
• In CLEAR state, the master is able to read the input data from the DP slaves. The master forces
the outputs to the slaves to be in a safe state (i.e. they contain only the value 0). For instance,
incorrect data transfer of a slave can cause the Profibus DP master to fall back from OPERATE
state to CLEAR state. Parameterization and configuration checks are possible in this state.
• In OPERATE state, unrestricted data transfer is possible. This data transfer is cyclic, i.e.
periodically, the input values are read from the slaves and the output data are written to the
slaves.
Changes of the operation mode are supervised by an internal state machine within the Profibus DP
master.
The system behaviour on the failure of a slave can be parameterized in the DP master, so that it
switches over automatically from OPERATE condition to the STOP condition. This also interrupts user
data transfer to all slaves and the module outputs are switched to the secure zero condition.
A change of the mode is indicated to the AP-task by the indication
“PROFIBUS_FSPMM_CMD_MODE_CHANGE_IND – Mode changed Indication”, see section 0.
If the AP-task wants to change the mode, it can accomplish this by sending the
“PROFIBUS_FSPMM_CMD_SET_MODE_REQ/CNF – Set a new Operation Mode” packet, which is
described, in section 6.1.3 of this document.
PROFIBUS DP-Master |
DOC061001API12EN | Revision 12 | English | 2010-12 | Released | Public © Hilscher, 2006-2010