Operating Instructions
IS1 PROFIBUS 3.00 E
- Technical alterations reserved -
32
PROFIBUS DP interface for IS1+
Switching logic and redundancy control in the AS
Check the availability of both transmission paths in the automation system by using an application program
and make one of the transmission paths active. Data can be exchanged between the application software and
the IS1+ fieldstation I/O modules only via the active transmission path.
The automation system monitors the redundant transmission paths by implementation and analysis of the
PROFIBUS service ‘Read Slave Diagnosis’.
In the first byte of the received diagnosis telegram, Bit No. 0 returns and indicates whether the addressed
PROFIBUS slave is involved in the cyclical data exchange or not.
After using this service for both CPUs, a logic in the AS helps to select one of the transmission paths (from
either CPU) to be activated. By transmitting the control register from the AS to the CPUs, the result of this
decision is notified to the CPUs, which react accordingly.
Switching logic in the AS for controlling the redundancy switching:
Analysis of
diagnosis telegrams
Left and right
CPU available ?
Left and right
CPU disturbed ?
Total loss of
IS1 Fieldstation
No switch over
Yes
Yes
No
No
Left CPU
disturbed ?
No
Activate right
CPU
Activate left
CPU
