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6. Redundancy with NX3030 CPU

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 User Information Exchanged between PLCA and PLCB

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 Exchange and Commands service is executed;

 Second, the Redundant Data Synchronization service is executed;

 Third, the Redundant Forcing List Synchronization service is executed.

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.

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 synchronization 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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