ProSoft Technology PTQ-PDPMV1 - Manual (Page 212)

Hot Standby Support PTQ-PDPMV1 ♦ Quantum Platform
User Manual PROFIBUS DP Master Network Interface Module for Quantum
Page 212 of 306 ProSoft Technology, Inc.
August 12, 2014
7.3.2 Switchover Timeline
The overall switchover time for a Hot Standby system depends on several
sequential events, which are outlined in the timeline below. The elapsed time
between some events is not static but highly dependent on the baud rate; these
events are indicated with bold text.
-1 Last DataExchange request before local (active) Master failure (that is, last re-
triggering of "slave watchdog").
0 Local (active) Master failure.
1 Remote (passive) Master detects counterpart failure.
2 Remote (passive) Master indicates the situation by clearing the COM-bit in Fieldbus
specific area.
3 Application of the remote (passive) Master detects that the local (active) Master has
failed and forwards this information to a higher-level system for further processing.
4 Application of the remote (passive) Master initiates a switchover based on the decision
from a higher-level system.
5 Remote (passive) Master performs the switchover (MAC reset with new TS)
6 Local (active) Master (former passive) issues an initial GlobalCtrl request (that is, first
PROFIBUS telegram after reinitialization of MAC).
7 Local (active) Master issues a SlaveDiag request to all slaves (first re-triggering of
"slave watchdog" after switchover).
8 Local (active) Master issues a DataExchange request to all slaves (second re-
triggering of "slave watchdog").
9 Local (active) Master sets the OD-bit in the Fieldbus specific area indicating that there
is fresh data in the output data area for the application to read.
10 Application of the local (active) Master detects that the OD-bit is set and accesses the
output area.
7.3.3 Bus Parameters
Some bus parameters need to be altered to allow for Hot Standby functionality.
Slave Watchdog Time (WD_Factor1&2)
The watchdog time of the slaves would have to be increased to allow for the
maximum time it takes for the HSBY system to perform a switchover.
Token Rotation Time (TTR)
To allow for Master-to-Master communication, TTR would have to be increased
by a factor of 2 relative to a single-Master configuration.