Communication via Function Blocks
6.4 Using the Function Blocks with the RK 512 Computer Connection
CP 341 Point-to-Point Communication, Installation and Parameter Assignment
Manual, 09/2008, A5E02191071-01
141
Data consistency
The block size limits the data consistency for data transmission between the CPU and
CP 341 to 32 bytes.
If you want consistent data transmission exceeding 32 bytes, you must take the following
into account:
●
Sender: Only access the send DB when all data have been completely transferred
(DONE = 1).
●
Fetching data: Only access the send DB when all data have been completely transferred
(DONE = 1).
●
Receiver: Use the interprocessor communication flag. Do not access the receive DB until
all data has been received (evaluation of the interprocessor communication flag specified
for this job; the interprocessor communication flag is available in the FB for one cycle, if
NDR = 1). After you have processed the received data, reset the interprocessor
communication flag to "0".
●
Providing data: Use the interprocessor communication flag. Do not access the provided
data until all of the data have been fetched (evaluation of the interprocessor
communication flag specified for this job). The interprocessor communication flag is
available for one cycle in the FB, if NDR = 1). After you have processed the data to be
fetched, reset the interprocessor communication flag to "0".
If your partner fetches data from the I (inputs), Q (outputs), M (bit memory), T (timers), or C
(counters) areas, the data consistency is limited to 32 bytes, provided you cannot use the
interprocessor communication flag to prevent other locations in the user program from
accessing these areas during the transmission.
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