Delayed Response And Parallel Accesses - Siemens Sentron 7KN POWERCENTER 1000 Manual

6.4.3

Delayed Response and parallel accesses

For many devices there is enough time to acknowledge the Modbus access within the
required response time.
The system however, usually composed of one 7KN Powercenter 1000 and the connected
circuit protection devices, is a spatially distributed system. This may lead to a delayed
response (Delayed Acknowledge DA) during write accesses via Modbus. If a write access to a
corresponding register is executed by the Modbus master, the following reactions may occur.
This behavior can occur with all registers from the following chapters with a write access
(0x06 or 0x10).
Request
Write (Register)
Write (Register)
Write (Register)
On the one hand, the states (Idle → Exception Code 05, Busy → Exception Code 06) are
monitored separately for each device or device address; on the other hand, a device can be
accessed in parallel by the three simultaneous connections, so Exception Code 06 must
generally be expected if the same terminal device receives several write requests from
different connections.
A terminal device should also only be parameterized from a physical connection. The Write
Requests should be performed sequentially on the same terminal device.
Note
To support multiple applications at the same time, it is necessary to clarify the Write
permissions at application level so that the applications do not influence each other, i.e.
changes are not overwritten by each other.
Therefore it is recommended to use only one application and to set parameters only via
powerconfig (mobile or PC) and to clearly define the responsibility.
Circuit protection devices with communication and metering function
System Manual, 06/2021, L1V30827018B-01
Response
OK
Delayed Acknowledge
Slave Device (= device ad-
dress) Busy
6.4 Modbus TCP connection
Example Further measures
Write response None
Exception Code 05 Function is formally correct,
is brought to execution.
Exception Code 06 Occurs if a Write has already
been sent for this terminal
device.
Renewed write access is only
possible if the previous Write
is completed.
Functions
65