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Cyclic transmission
4.7.1 Common memory
Concept of common memory is stated below.
The common memory is used as a shared memory between nodes which perform cyclic transmission.
The common memory has two areas which are "common memory area 1" and "common memory area 2".
Common memory area 1 is I/O data area. Common memory area 2 is the control information area.
Two different areas can be assigned to each node.
When the area each node sends exceed the transmission size (1024 bytes) by one frame, data is transmitted by multiple
frames.
When receiving data which are divided into multiple frames as above, common memory is not updated until all frames sent
from one node are received. Synchronism per node unit is guaranteed.
Entire network has an area of 8k bits (0.5k word) + 8k words = 8.5k words.
The maximum send data capacity per one node is 8.5k words. (Note that one word is 2 bytes.)
Among common memory, both common memory area 1 and common memory 2 can be set as a transmission area of one
node as desired within the maximum area.
Each node on FL remote network can share the same data in the whole system by broadcasting data at a constant period.
In addition, each node has own transmission area which does not overlap each other to exchange data. (For common
memory function, the transmission area assigned to one node is a receive area for other nodes.)
2
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2
0
0.5k Word
8k Words
=Input/output data area
Common memory area 1
Common memory
area
8.5k Words
=Control information area
Common memory area 2
(Send)
Common memory
of node = 01
Common memory
of node = 02
Common memory
of node = 03
Common memory
of node = 04
(Receive)
(Receive)
(Receive)
(Receive)
(Receive)
(Receive)
(Receive)
(Receive)
(Receive)
(Receive)
(Receive)
(Receive)
(Send)
(Send)
(Send)