6. REDUNDANCY WITH NX3030 CPU
RedUsrLoc: has 128 bytes of data filled freely by the user (e.g. communication diagnostics with a SCADA system).
These 128 bytes of data can be interchanged with the other CPU (remote)
RedUsrRem: it’s a copy from the other CPU RedUsrLoc, received through NETA/NETB
On Redundancy Maintenance section, the following sub-sections offer more details regarding these data structures:
Redundancy Diagnostics Structure
Redundancy Commands
User Information Exchanged between PLCA and PLCB
6.3.6. Cyclic Synchronization Services through NETA and NETB
This section describes the three synchronization services which occur cyclically in a redundant CPU between PLCA and
PLCB, through NETA and NETB synchronism channels.
These services are executed at the beginning of each MainTask cycle, and in the sequence which they appear below:
First, the Diagnostics and Commands Exchange service is executed
Second, the Redundant Data Synchronization service is executed
Third, the Redundant Forcing List Synchronization service is executed
6.3.6.1. Diagnostics and Commands Exchange
This service is responsible by the interchange of the following data structures, in each MainTask cycle:
To copy RedDgnLoc from PLCA to PLCB RedDgnRem
To copy RedCmdLoc from PLCA to PLCB RedCmdRem
To copy RedUsrLoc from PLCA to PLCB RedUsrRem
To copy RedDgnLoc from PLCB to PLCA RedDgnRem
To copy RedCmdLoc from PLCB to PLCA RedCmdRem
To copy RedUsrLoc from PLCB to PLCA RedUsrRem
The service will be executed using only one synchronism channel (NETA or NETB). This way the service can be completed
even if one channel has problems.
6.3.6.2. Redundant Data Synchronization
This service is responsible for the redundant variables transferring, from the Active CPU to the Inactive CPU. As previously
described, there are symbolic redundant variables and also redundant direct representation variables (%I, %M and %Q).
For this service to be executed, several conditions must be satisfied:
The previous synchronization service in this MainTask cycle (Diagnostics and Commands Exchange) must be completed
with success.
In case this CPU is in Active state, the other must be in Non-Active state. On the other hand, in case this CPU is in
Non-Active state, the other must be in Active state.
Both projects (2 CPUs) must be identical, except when the project automatic synchronization is disabled (see Project
Synchronization Disabling) section.
At least one synchronism channel (NETA and/or NETB) must be operational. If both synchronism channels (NETA
and NETB) are operational, the communication is distributed between both (load balances) in order to reduce the syn-
chronization time. In case only one channel is operational, the synchronism will continue to be executed only by this
channel, keeping the redundant data synchronization.
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