ProSoft Technology PLX8X-MNET-61850 - Manual (Page 143)

PLX8x-MNET-61850 ♦ Communication Gateway Reference
Modbus TCP/IP to IEC 61850 User Manual
ProSoft Technology, Inc. Page 143 of 228
May 14, 2014
6.3 ProSoft gateway
6.3.1 Asynchronous Processes
The gateway has a number of processes and drivers running in it in a
multitasking firmware environment. An IEC 61850 Client driver, a Modbus
TCP/IP Client driver, and a Modbus TCP/IP server driver operate asynchronously
within this multitasking environment, along with other firmware processes. The
drivers are independently processing the commands and messages in their
queues as quickly as possible, giving priority to GOOSE messages.
The Modbus TCP/IP Client driver processes commands that have been enabled
for continuous execution in the command list, starting with the first command and
going through them sequentially until it gets to the last one. After the last
command in the list has been completed, the driver starts over again at the first
command and continues to cycle through the list, over and over again, as quickly
as possible. The larger the Client Command List is, the longer it takes the driver
to cycle through the list.
Meanwhile, the IEC 61850 Client may be receiving large amounts of data from
the configured IEDs. If so, the IEC 61850 Client will be updating the Tag
Database with data coming from the IEDs asynchronously from what’s
happening with the MNET Client driver.
Since the different drivers run asynchronously from each other and depending
upon how fast or how often IEDs send data, it is possible that a tag in the tag
database may be updated more than one time by the IEC 61850 Client driver
before the Modbus TCP/IP Client driver sees the update and can send the data
to a Modbus server.
IED data changes are not buffered, so, the Modbus TCP/IP Client driver may not
be able to transfer every data change that happens in the IEC 61850 Client tag
database. Only the data most recently stored in the tag database by the IEC
61850 Client driver will be available for the MNET Client driver to transfer to
Modbus Devices. So, it is possible that some changes in data values on some
IEDs may be lost in the process, especially during times of high volume IED data
traffic.