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Appendix D
FL-net Network Control
FL-net Token Control
Tokens
Basically, a node can send data when it is holding the token. The only two types of data that can be sent by a
node that is not holding the token are a request to resend the token when a token monitoring timeout occurs
and a participation request frame for a node that is not participating in the network.
1. FL-net networks pass a single token between nodes.
2. After each node receives the token, it maintains the right to transmit in the network until the token is passed
to the next node.
3. The token is passed to all nodes participating in FL-net.
4. The token can be sent together with cyclic data.
5. The token can also be passed alone without attached data.
6. The token is monitored by a timer and automatically resent if it is not passed through the network within a
fixed period of time.
7. If two or more tokens are present in the network at the same time, they will be reduced to a single token.
Token Flow
Generally, only a single token is present in a network at any one time. If two or more tokens are present in the
network, the token at the node with the smallest destination node number is given priority, and the other tokens
are discarded. The token frame is the frame that includes the token and consists of the token's destination
node number and source node number. Each node becomes the token holding node when its node number
matches the token destination node number in the received token frame. The token rotation order is deter-
mined by the node numbers. The token is passed to all nodes registered in the participating node management
table in ascending order. The node with the largest node number in the network passes the token to the node
with the smallest node number in the network.
Token passed to next token.
Node N
−
1
Node N
Node 1
Node 2
Node 3
Token passed to node with lowest
node number.