Operating Instructions
IS1 PROFIBUS 3.00 E
- Technical alterations reserved -
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PROFIBUS DP interface for IS1+
Behavior of IS1+ CPU
Parallel cyclical data traffic can be defined via PROFIBUS DP for both CPUs (both CPUs are in data
exchange).
Both CPUs in an IS1+ fieldstation are connected with the non-redundant installed I/O modules.
The two CPUs in an IS1+ fieldstation are not allowed simultaneous access to the I/O modules. For this reason,
only one CPU is switched to active status by a control register from the AS software.
The active CPU takes over the access to the I/O modules (read and write).
The other CPU
is in the ‘inactive’ status. The active CPU updates the input data in the inactive CPU in a cycle
and monitors it for correct operation.
As a result, input data can be read cyclically by both CPUs, in error free standard operation mode.
The data between the active CPU and the inactive CPU can be different in case of error! Therefore the data
of the inactive CPU should not be used for the application software.
Although the automation system does
receive output data in ‘inactive’ status via the PROFIBUS and this data
is stored in the CPU RAM, it is, however, not forwarded to the output modules.
Control and Status register CPU
The CPU to be activated is selected by a logic in the AS.
Either CPU in a redundant IS1+ fieldstation can be enabled by writing a control register from the automation
system for both CPUs.
The selected (active) CPU is permanently (cyclically) controlled with the respective control code. This facilitates
automatic restart after malfunctions. The control register for switching to redundancy is updated with identical
content for both CPUs (prim. and red.).
Coding of the control register see
The actual status of the two redundant CPUs can be read from the
2.10.2.3
Timeout time for Output modules
If an active transmission route fails, the cyclical updating of the output module stops. There are Watchdog
circuits on the output modules that monitor the cyclical data transmission between the CPU and the output
modules.
If no valid data is transmitted to the output module beyond the time T
Mod
, the module places its outputs in safety
position. This should not be done for error-free redundancy switching.
This produces the following requirement for error-free switching:
The maximum switching time is defined by the parameterized DP master bus cycle, the PROFIBUS baud
rate, the monitoring software cycle time in the automation system and the startup delay of the CPU (< 500
ms).
The IS1 timeout time for output modules (T
MOD
) can be parameterized in the DP master in the range of 100
ms to 25.5 sec. (default value: 1 s).
Parameterising rule for the timeout for output modules (T
Mod
):
T
Mod
must be parameterised
greater
than the maximum total time between the occurrence of a
transmission error and the activation of the hitherto inactive CPU (switching time).
