YOKOGAWA STARDOM FCN-500, Инструкция по эксплуатации

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<9. Advanced Engineering >
170
TI 34P02K35-02E May 31, 2017-00
TIP
The CONNECT and SD_CFCX_CONNECT_EX function blocks for connection have identical functions
except that the assignment of destination IP address and communication port is simple for
SD_CFCX_CONNECT_EX so its use is recommended.
● Characteristics and Limitations of Confirmed Communication
Characteristics
In confirmed communication, READ and WRITE are used as function blocks for data
receiving and sending.
Confirmed communication allows the source FCN-500 or FCN-RTU to receive
responses for READ/WRITE requests from a destination FCN-500 or FCN-RTU, as
well as to detect communication errors if no response is received. Communication
errors may be due to CPU module failure of the destination FCN/FCJ,
communication interruption caused by CPU load increase or communication
interruption caused by failure of communication equipment or cables.
Moreover, as the source FCN-500 or FCN-RTU directly reads from and writes to
variables of the destination FCN-500 or FCN-RTU, a READ/WRITE application
needs to be created only on the source FCN-500 or FCN-RTU but not on the
destination FCN-500 or FCN-RTU.
In the figure below, FCX01 writes data directly into variables of FCX02, and reads
data of variables of FCX02 directly.
FCX02
Function block for
connection
FCX01
Function block for
sending
Transmission
data
Function block for
connection
Connection
Variables
written into
Variables
read from Function block for
receiving
Received
data
Limitations
As described earlier, in confirmed communication, a source FCN/FCJ directly
accesses the variables of the destination FCN/FCJ to read and write data. For this
function to work, the PDD (Process Data Directory) property must be turned on for
the destination variables.
By adding the PDD property, variable data is stored in the PDD database to enable
directly reading and writing by other FCN/FCJs.
However, as PDD has a size limitation, and the process alarm function of
NPAS_POU also uses the PDD, if much data is communicated via confirmed
communication, the number of NPAS POUs that can be defined is reduced.
Moreover, as writable name of destination FCN-500 or FCN-RTU is specified in
source FCN-500 or FCN-RTU, any change in the instance name of destination
variables will require modification of the application on the source FCN-500 or FCN-
RTU.