Siemens SIPROTEC Manual page 25

Master Primary /
Master Backup
Toggle bits
SIPROTEC PROFIBUS DP - Bus mapping 6MD662/3/4
C53000-L1840-B011-03
The PROFIBUS DP master sends its redundancy state to the slave using these two
bits. This can initiate a redundancy switchover if it corresponds to the current state of
the slave module.
• Bit 3 = 0 and bit 2 = 1: Master is BACKUP
• Bit 3 = 1 and Bit 2 = 0: Master is PRIMARY
If both bits are set identically (both equal 0 or both equal 1) then this is treated as "Mas-
ter is BACKUP" by the slave.
A watchdog timer in the PROFIBUS DP slave is used as the default mechanism for
the supervision of the PROFIBUS DP communication.
This timer is loaded the first time
BUS DP master and will be re-triggered every time a telegram to the slave is received.
The watchdog timer expires in case of a communication interruption.
With that, the PROFIBUS DP slave can detect a communication failure and react on
it if necessary.
An (optional) communication supervision on application level is implemented in the
redundant PROFIBUS DP slave of the SIPROTEC devices in addition to the above
mentioned response monitoring mechanism with the watchdog timer.
For this, the two Toggle bits in each of the bytes "Control_O_1" and "Control_I_1" are
used.
These bits have to be toggled (from '10' to '01' or vice versa) at least ones in a pre-
defined time period by the PROFIBUS DP master or the program in the PLC.
If an invalid bit combination '11' or '00' is received in the Toggle bits then this is treated
as "not toggled".
The slave mirrors the Toggle bits which were received in "Control_O_1" byte from the
PROFIBUS DP master back to the master in the "Control_I_1" byte.
The time period within which the Toggle bits have to be changed can be set up during
configuration of the bus specific parameters in DIGSI (ref. to chap. 1.3.1.2).
If no Toggle bit change to a valid bit combination is detected within the configured time
period then this is treated as a communication failure:
• The slave leaves data exchange and expects new parameterization and configura-
tion from the master.
• A redundancy switchover to BACKUP is executed if the module was PRIMARY till
now.
• A communication failure is signaled to the device for this module.
The tagging "SysIntErr" will be set to ON in the device if the partner module also
has communication interruption to its PROFIBUS DP master (ref. to chap. 1.3.2.1).
The Toggle bit supervision starts when after entering data exchange with the master
a changeover from a valid Toggle bit combination to the other valid Toggle bit combi-
nation is detected by the PROFIBUS DP slave.
As long as the Toggle bit supervision is not started in the slave, a communication fail-
ure is signaled to the device for this module.
1. The reload value for this watchdog timer (response monitoring timer) is calculated by the
PROFIBUS DP master with the network size, the baud rate etc. This reload value then
is sent as part of the Set_Prm telegram to the slave.
Redundant PROFIBUS DP interface
1
if the slave enters data exchange with the PROFI-
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