Hitachi FL.NET, User Manual

Page: 75 / 307

5 USER GUIDE
5-23
(4) Data synchronicity assurance
In cyclic transmission, the data to be transmitted is divided into frames depending its size.
The following procedures are used to assure common memory (internal memory such as the
FL.NET module) synchronicity on an individual node basis.
Transmission timing
When a data transmission is requested by a higher layer, the cyclic data of the self-node is
copied to a buffer to prepare for transmission and then sequentially transmitted. If the size
of the data retained by a transmitting node is larger than the maximum permissible size limit
for the transmission of one frame, the buffered data is divided into two or more frames for
transmission.
Reception sequence refresh timing
When a receiving node completely receives cyclic data from another node, it refreshes the
associated area while maintaining the synchronicity with a higher layer.
Even when cyclic data is transmitted after being divided into two or more frames, the
associated area refreshes when all the frames sent from a node are completely received. If
all such transmitted frames are not received, the entire data received from the transmitting
node is discarded.
Transmission
area
Send buffer
Cyclic data
Cyclic data
Cyclic data
Receive buffer
Reception
area
Collective copying
Collective copying
Transmitting end
Receiving end
On network
circuit
Common memory
Common memory
Figure 5-24 Data Synchronicity Assurance