ProSoft Technology PTQ-PDPMV1 - Manual (Page 193)

PTQ-PDPMV1 ♦ Quantum Platform Hot Standby Support
PROFIBUS DP Master Network Interface Module for Quantum User Manual
ProSoft Technology, Inc. Page 193 of 306
August 12, 2014
7.2.5 Transition Description
Offline to Standby (1)
 The remote (passive) Master would attain its node address by subtracting
one (1) from the address derived from the database. For example, if the
Master address in the database equals 2, the remote (passive) Master would
use address 1. If the Master address in the database equals 0, it would use
address 125.
 After a switchover, it is important that the previously local (active) Master
does not become passive before the counterpart has switched to active. If
this statement is not adhered to, a dangerous situation with two Masters
having the same address (two remote (passive) Masters in this case) would
arise. The result of such a situation would be very unpredictable since there
is really no way of detecting it.
Offline to Primary (2)
See Standby to Primary considerations.
Standby to Primary (3)
It is important that the Master becomes active before the watchdog of the slaves
expires. To allow for this switchover time, the watchdog value would have to be
extended in the bus parameter settings.
When the remote (passive) Master switches to active, it would change its node
address to the primary address. To achieve this, the ASPC2 must be reset and
reinitialized with the new bus parameter TS. Note that it is just the ASPC2 that is
reinitialized, not the entire Master module.
 The state of the "PA-bit" in register "HSBY Local status" would change to 0,
indicating that the Master module now operates as local (active) Master.
 When the remote (passive) Master switches to active, it will not re-
parameterize the slaves that report being in the "DATA" state.
 After a switchover, the application will be informed when there is valid data
available in the input output image area.
 Primary obtains the Master node address.
Primary to Offline (4)
The local (active) Master leaves the bus as fast as possible since the risk of
having two Masters with the same address after a switchover must be avoided
(two local (active) Masters in this case). The time it takes for leaving the bus will
not exceed the switchover time.