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Chapter 7: Computer Link Function
7
(2) Common memory
The description of the common memory is as follows.
1 The common memory allows the memory to be shared between nodes performing a cyclic
transfer.
2 Two types of areas (area 1 and area 2) are allocated for each node.
3 If an area needed by a node to send its data exceeds the transfer size allowed for one frame,
namely, more than 1024 bytes, the node should use multiple frames to send the data.
4 When receiving multiple frames of related data, as described in point 3) above, the common
memory does not renew the common memory details until it has received all of the frames
being sent by one node. In other words, it guarantees simultaneity of each node.
(However, if the data in area 2 exceeds 3084 bytes, the JW-50FL cannot guarantee
simultaneity for hardware reasons.)
5 8 K bits + 8 K words = 8.5 K words (fixed) of common memory must be reserved in the node
communication section.
6The size of areas 1 and 2, used as the sending area for one node in the common memory, can
be specified as any size within the maximum size allowed for the area.
7 Since each node broadcasts data with a certain interval, it provides a function for sharing the
same data throughout the system. Each node in an FL-net is assigned a sending area that
does not overlap with the others for exchanging data. In common memory operations, the
sending area for one node will be the receiving area for another node.
Example 1: Common memory during a cyclic transfer
(Send)
(Receive)
Node 02
Node 01
common memory
(Receive)
(Receive)
(Send)
(Receive)
(Receive)
(Receive)
(Send)
(Receive)
(Receive)
(Receive)
(Send)
(Receive)
(Receive)
(Receive)
Node 04Node 03