Hitachi FL.NET User Manual page 68

(2) Common memory
The ideas of the common memory are described below.
Furnishes the nodes conducting cyclic transmission with functions that can be handled as
the functions of the common memory.
Two areas (Area 1 and 2) can be allocated for one node.
Two or more frames are used for data transmission when the 1,024-byte transmission size
limit per frame is exceeded by an area transmitted by one node.
In the reception of data divided into two or more frames, the common memory does not
refresh until all the frames coming from a node are completely received.
The common memory size furnished by the communication section of one node is fixed at
8.5k words (= 8k bits + 8k words).
As the common memory's transmission area for one node, Area 1 and 2 can be both set up
as desired as far as the maximum permissible size is not exceeded.
The same data can be shared by the entire system when individual nodes broadcast data at
fixed intervals. Nodes on the FL-net exchange data by using their own transmission
areas that do not overlap with those of the other nodes. In a common memory operation,
the transmission area allocated for one node is the reception area for another node.
Common memory
for Node 01
(Transmission)
(Reception)
・
・
(Reception)
・
・
(Reception)
Figure 5-14 Cyclic Transmission Common Memory Area Example 1
Common memory
for Node 02
(Reception)
(Transmission)
・
・
(Reception)
・
・
(Reception)
5-13
Common memory
for Node 03
(Reception)
(Reception)
・
・
(Reception)
・
・
(Transmission)
5 USER GUIDE
Common memory
for Node 04
(Reception)
(Reception)
・
・
(Transmission)
・
・
(Reception)