5. CONFIGURATION
transmitted to the IEC 60870-5-104 client.
In Nexto Series case, there are no diagnostics available to watch the CPU’s events queue occupation, not even information
about the queue overflow. However the consumers have a diagnostics group referred to its events queue. Further information
can be found at the specific driver communication section.
5.5.3.2.1. Overflow Sign
The overflow sign to the consumers’ events queue occurs in two situations:
When the consumer events queue is out of space to store new events
If the CPU aborted the event generation (because occurred to more events in a single execution cycle than the events
queue total size)
5.5.3.3. Producers
The producers are typically communication drivers or PLC internal elements that are capable to generate events. The
previous figure show some examples.
Internal Points: This is a PLC’s firmware internal element, which detects events each execution cycle (MainTask)
to those communication points that don’t have a defined origin and then inserts the events in the CPU’s queue. The
maximum number of events that can be detected in each MainTask cycle is equal to the CPU’s events queue size. In case
the number of generated events is bigger than this, in a single cycle, the exceeding are going to be lost.
MODBUS Driver (Client/Server/Master/Slave): The variables value change caused by MODBUS read/write are de-
tected at each MainTask cycle and then the events are inserted in CPU’s queue. In Client/Master cases, are also generated
quality events when there is a communication failure with the slave device.
5.5.4. Interception of Commands Coming from the Control Center
The Nexto PLC has a function block that allows selection commands and operation to the output points received by server
drivers (IEC 60870-5-104 Server) been treated by the user logic. This resource allows the interlocking implementation, as well
as the handling of the received command data in the user logic, or yet the command redirecting to different IEDs.
The commands interception is implemented by the CommandReceiver function block, defined in the LibRtuStandard. The
input and output parameters are described on the following tables:
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