10.2 Multiprocessor Communication
Definition
Multiprocessor communication means the exchange of larger
amounts of data (data blocks) between CPUs operating in the
multiprocessor mode. The COR C is necessary for multiprocessor
communication.
10.2.1
Introduction To transfer data blocks, or to be more precise, blocks of data with a
maximum length of 64 bytes (= 32 data words), you can use the
following special functions that are integrated in the CPU:
•• OB 200: INITIALIZE: preassign
•• OB 202: SEND: send a field of data
•• OB 203: SEND TEST: test sending capacity
•• OB 204: RECEIVE: receive a data field
•• OB 205: RECEIVE TEST: test receiving capacity
The special function OBs, OB 200 and OB 202 to OB 205 are simply
called "communication OBs" in the following sections.
Required knowledge
To use these functions, you only require basic knowledge of the
STEP 5 programming language and the way in which SIMATIC S5
programmable controllers operate. You can obtain this basic
information from the publications listed in the Further Reading.
Basic sequence
To transfer data, you must activate the SEND function on the
transmitting CPU and the RECEIVE function on the receiving CPU.
The data words of a DB or DX data block located in the transmitting
CPU are transported via the coordinator 923C to the receiving CPU
one after the other and written to the DB or DX data block with the
same number and under the same data word address; i.e. this
represents a "1:1" copy operation.
Data fields
The amount of data that can be transferred with the SEND and
RECEIVE functions is normally 32 words.
If the block length (without header) is not a multiple of 32 words, the
last field of data to be transferred is an exception and is less than 32
words long.
Multiprocessor Communication
CPU 948 Programming Guide
C79000-G8576-C848-04
10 - 15
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