10.2.6
Calling Communication OBs
Proceed as follows:
1. Call the INITIALIZE function only in the cold restart
organization block OB 20 on one CPU.
2. Call the SEND, SEND TEST, RECEIVE, RECEIVE TEST
functions either only within the cyclic program or only within the
time-driven program.
Double call
Depending on the assignment of parameters in DX 0 ("interrupts at
operation boundaries"), and the type of program execution (WARM
RESTART, interrupt handling, e.g. OB 26 for cycle time error) it is
possible that one of the functions INITIALIZE, SEND, SEND TEST,
RECEIVE and RECEIVE TEST can be interrupted.
If a user interface inserted at the point of interruption also contains one
of the functions SEND, SEND TEST, RECEIVE and RECEIVE
TEST an illegal call (double call) is recognized and an error is
signalled (error number 67, Section 10.2.8).
Parallel processing
Once you have completed the assignment of the buffer (INITIALIZE
function), you can execute the functions SEND, SEND TEST,
RECEIVE and RECEIVE TEST in any combination and with any
parameter assignment in all the CPUs simultaneously and parallel to
each other.
Taking a single link (e.g. from CPU 2 to CPU 3) it is possible to
execute the SEND function (CPU 2) and the RECEIVE function
(CPU 3) simultaneously. While CPU 2 is sending data fields to the
coordinator, CPU 3 can already receive (fetch) buffered data fileds
from the coordinator.
Areas occupied
The communication OBs do not require a working area (for buffering
variables) and do not call data blocks. They do, of course, access areas
containing parameters, although only the parameters marked as output
parameters are modified.
Multiprocessor Communication
CPU 948 Programming Guide
10 - 22 C79000-G8576-C848-04
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