Figure 5-2 Fa Link Protocol - Hitachi FL.NET User Manual

(2) FL-net protocol
The FL-net consists of six protocol layers as shown in Figure 5-2.
The transport layer and network layer use UDP/IP, whereas the data link layer and physical
layer use Ethernet.
Application layer
FA link protocol layer
Transport layer
Network layer
Data link layer
Physical layer
(3) FL-net transmission system features
The features of the FL-net FA link protocol layer are outlined below:
• Masterless, token-based transmission management is exercised to avoid collisions.
• A token can be circulated at fixed intervals to define the refresh cycle time.
• A predetermined token is transmitted together with cyclic data.
• At startup, a token is transmitted from a node having the lowest node number.
• If a token is not transmitted for a predetermined period of time, the next node transmits a
node.
• Thanks to the use of a masterless, token-based system, network inoperativeness can be
avoided even when some nodes become faulty.
• Operating mode (RUN/STOP), hardware error (ALARM), and other information
management tables are available for referencing the operating status of the other nodes.
Cyclic
transmission

Figure 5-2 FA Link Protocol

5-3
Controller interface
Service function
Message transmission
Token function
UDP
IP
Ethernet
(IEEE 802.3-compliant)
5 USER GUIDE
FL-net
protocol