ProSoft Technology PTQ-PDPMV1 - Manual (Page 197)

PTQ-PDPMV1 ♦ Quantum Platform Hot Standby Support
PROFIBUS DP Master Network Interface Module for Quantum User Manual
ProSoft Technology, Inc. Page 197 of 306
August 12, 2014
Remote (passive) Master operational prior to active
As soon as the remote (passive) Master is ready to communicate on the
PROFIBUS network, it would start sending ping messages to the local (active)
one. As soon as the local (active) Master responds, the COM-bit is altered from
zero to one.
Remote (passive) Master failure
When the local (active) Master has not received any ping messages from the
counterpart within TA, it would clear the COM-bit. This scenario would also apply
when the field bus link between the two Masters is lost, due to a cable break, for
example.