4. Configuration
173
Protocol IEC 60870-5-104 object type
No additional definition
(default)
Same behavior of
persistent qualifier
Same behavior of short
pulse qualifier
Same behavior of short
pulse qualifier
Requires command
interception to application
treatment. Other way it will
return a negative
acknowledge message
(fail).
Requires command
interception to application
treatment. Other way it will
return a negative
acknowledge message
(fail).
Requires command
interception to application
treatment. Other way it will
return a negative
acknowledge message
(fail).
The output is going to be
on or off and that will
remain until new
command, according to
value (ON or OFF)
commanded by the client.
Table 4-110. Server IEC 60870-5-104 Commands Qualifier
Notes:
Command Interception: For futher information about commands intrception of IEC 608705-104
clients, consult section Interception of Commands Coming from the Control Center, implemented
through CommandReceiver function block.
Communication Performance
MODBUS Server
The MODBUS devices configurable in the Nexto CPU run in the background, with a priority below
the user application and cyclically. Thus, their performance varies depending on the remaining time,
taking into account the difference between the interval and time that the application takes to run. For
example, a MODBUS device in an application that runs every 100 ms, with a running time of 50 ms,
will have a lower performance than an application running every 50 ms to 200 ms of interval. It
happens because in the latter case, the CPU will have a longer time between each MainTask cycle to
perform the tasks with lower priority.
It also has to be taken into account the number of cycles that the device, slave or server takes to
respond to a request. To process and transmit a response, a MODBUS RTU Slave will takes cycles
(cycle time of the MODBUS task), whereas a MODBUS Ethernet Server task takes only one cycle.
But this is the minimum time between receipt of a request and the reply. If the request is sent
immediately after the execution of a task MODBUS cycle time may be equal to 2 or 3 times the cycle
time for the MODBUS slave and from 1 to 2 times the cycle time for the MODBUS server.
In this case: Maximum Response Time = 3 * (cycle time) + (time of execution of the tasks) + time
interframe chars) + (send delay).
For example, for a MODBUS Ethernet Server task with a cycle of 50 ms, an application that runs for
60 ms every 100 ms, the server is able to run only one cycle between each cycle of the application.
On the other hand, using the same application, running for 60 ms, but with an interval of 500 ms, the
MODBUS performs better, because while the application is not running, it will be running every 50
ms and only each cycle of MainTask it will take longer to run. For these cases, the worst performance
will be the sum of the Execution Time of the user application with the cycle time of the MODBUS
task.
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