Chapter 7: Computer Link Function
(2)Common memory
The description of the common memory is as follows.
1The common memory allows the memory to be shared between nodes performing a cyclic transfer.
2Two types of areas (area 1 and area 2) are allocated for each node.
3If 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.
4When 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
58 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.
7Since each node broadcasts data with a certain interval, it provides a function for sharing the
7 | same data throughout the system. Each node in an | |
does not overlap with the others for exchanging data. In common memory operations, the | ||
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| sending area for one node will be the receiving area for another node. |
Node 01 |
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common memory | Node 02 | Node 03 | Node 04 |
(Send) | (Receive) | (Receive) | (Receive) |
(Receive) | (Send) | (Receive) | (Receive) |
(Receive) | (Receive) | (Receive) | (Send) |
(Receive) | (Receive) | (Send) | (Receive) |
Example 1: Common memory during a cyclic transfer