Using The Function Blocks With The 3964(R) Procedure - Siemens Simatic S7-300 CP 341 User Manual

6.3

Using the Function Blocks with the 3964(R) Procedure

The function blocks available for connection to a communication partner with the 3964(R)
procedure are as follows:
● FB 8 P_SND_RK for transmitting data
● FB 7 P_RCV_RK for receiving data
Requests that can be processed simultaneously
Only one FB P_SND_RK and one FB P_RCV_RK can be programmed for each CP 341 in
the user program.
Bear in mind, too, that you can use only:
● 1 instance data block for FB P_SND_RK and
● 1 instance data block for FB P_RCV_RK
This is because the statuses needed for the FB's internal routines are stored in the instance
data block.
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).
● Receiver: Only access the receive DB when all data are received (NDR = 1). Then you
must disable the receive DB (EN_R = 0) until you have processed the data.
CP 341 Point-to-Point Communication, Installation and Parameter Assignment
Manual, 09/2008, A5E02191071-01
www.gkbpx.com
6.3 Using the Function Blocks with the 3964(R) Procedure
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Communication via Function Blocks
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