Parameterization and commissioning
EL6731 115Version: 2.8
5.1.8.2 Error Reactions
Failure of a slave
If a slave does not respond or the response is faulty, the master repeats the telegram several times,
according to the Max Retry Limit (see Bus parameters [}87] dialog). If a faulty telegram is received, the
master repeats immediately, in the event of a timeout the master waits for a response from the slave until the
Slot Time has elapsed (see Bus parameters [}87] dialog). At 12 Mbaud, a slot time of 1000 bit-periods and
a max retry limit of 4 (the default values) then a Data_Exchange telegram will delay sending the following
telegram by
TDelay = (4 x ((15 + number of outputs) x 11 + 1000) - (15 + number of inputs) x 11)/12 µs
The DpState [}121] of the slave is set to 0x02 (timeout) or 0x0B (faulty telegram). The effect on the DP
connection can be set (see below).
Normal DP cycle (12 Mbaud, 5 slaves, an average of 20 bytes I, 20 bytes O for each slave)
Fig.115: Diagram showing a normal DP cycle
First occurrence of a faulty DP cycle (slave 3 does not answer)
Fig.116: Diagram showing the first occurrence of a faulty DP cycle
Subsequent DP cycles (slave 3 no longer in the polling list)
Fig.117: Diagram showing subsequent DP cycles
It can still happen that the slave answers incorrectly (e.g. because, as a result of a local event on the slave,
the DP connection has been removed). In this case, the telegram is not repeated, but the system continues
by sending the next telegram. The DpState [}121] is set to a value other than 0, the slave is removed from
the polling list and is no longer addressed in the following DP cycle (which means that the time at which the
following telegram is sent changes), until the DP connection can be established again.
Reactions in the master
The master's reactions can be set differently for each slave (see the tab for the slave's Features [}97]).
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